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Characterization of Staphylococcus aureus infections in children with Down syndrome
J Infect Chemother 21 (2015) 790e794
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Original article
Characterization of Staphylococcus aureus infections in children with Down syndrome Jeffrey N. Johnston, Sheldon L. Kaplan, Edward O. Mason, Kristina G. Hulten* Texas Children's Hospital, Department of Pediatrics, Section of Infectious Diseases, Baylor College of Medicine, Houston, TX, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 April 2015 Received in revised form 3 August 2015 Accepted 4 August 2015 Available online 18 September 2015
Staphylococcus aureus infections in the Down syndrome (DS) population have not been well characterized. This study determined clinical and molecular characteristics of S. aureus infections in children with DS followed at Texas Children's Hospital (TCH), from 2001 to 2011. Patients were retrospectively identified from an ongoing S. aureus surveillance study. Medical records were reviewed. Isolates were characterized by antimicrobial susceptibility, pulsed-field gel electrophoresis patterns, and detection of PVL genes (pvl), mupA (high-level mupirocin resistance gene), smr (chlorhexidine resistance conferring gene), and Staphylococcal Chromosomal Cassette mec (SCCmec) type. Twenty-six patients with DS had a total of 34 S. aureus infections (8 recurrent); 61% were MRSA. DS patients represented 16.8 per 10,000 community onset S. aureus infections seen at TCH. Among 26 initial infections 17 were skin and soft tissue (SSTI), 7 were outer or middle ear and 2 were invasive infections. Seventeen patients were hospitalized. Thirteen (65%) of 20 available isolates were USA300, 14 were pvlþ, 5 were mupAþ, and 8 were smrþ. Five of 8 (63%) recurrent infections were ear infections. All 4 recurrent ear isolates available for study were smrþ, ciprofloxacin non-susceptible and treated with ciprofloxacin otic drops. S. aureus infections among patients with DS were similar in presentation to other patient groups, except for a greater proportion being associated with ear infections. Seventy percent of ear fluid isolates carried antiseptic and fluoroquinolone resistance genes. A study of a greater number of DS patients is warranted to further explore these findings. © 2015, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
Keywords: Staphylococcus aureus Down syndrome Pediatric smr mupA
1. Introduction Down syndrome is the most common chromosomal abnormality of live births. The prevalence of Down syndrome has been steadily increasing in the United States and currently affects one in 740 live births, or 13.51/10,000 live births [1]. Children with Down syndrome frequently require medical care for a variety of problems, including more frequent infections; a result of both immunological and anatomical factors. The altered upper airway anatomy increases the risk of Eustachian tube dysfunction and likely plays a role in chronic and recurrent otitis media as well as other upper respiratory tract infections [2]. Atopic dermatitis and skin infections are also common.
* Corresponding author. 1102 Bates St. Suite 1150, Houston, TX, 77030, United States. Tel.: þ1 832 824 4325; fax: þ1 832 825 4347. E-mail address: [email protected] (K.G. Hulten).
Staphylococcus aureus infections are common in the general pediatric population in the United States; no study has described the clinical spectrum and epidemiology of these infections in the Down syndrome patient population. In the United States, the most common community acquired strain, USA300, is associated with the cytotoxin Panton-Valentine leukocidin (PVL) and increased rates of complications in otherwise healthy individuals [3e7]. USA300 methicillin resistant S. aureus (MRSA) isolates carry the 21e25 kb Staphylococcal Cassette Chromsome mec (SCCmec) IV, incurring resistance to beta-lactam antibiotics, while frequently remaining susceptible to many non-beta lactam antibiotics [8]. Exposure to the healthcare setting, medical interventions and use of antibiotics are risk factors in acquiring infections with bacterial strains carrying antibiotic resistance markers [9]. Among these, genes conferring resistance to mupirocin or chlorhexidine have been reported to increase in prevalence among S. aureus isolates [10e12]. The mupA gene is commonly plasmid mediated, confers high-level resistance to mupirocin and has been linked to
http://dx.doi.org/10.1016/j.jiac.2015.08.002 1341-321X/© 2015, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
J.N. Johnston et al. / J Infect Chemother 21 (2015) 790e794
decreased efficacy of nasal decolonization protocols [13]. mupA positive S. aureus strains have been associated with additional antimicrobial resistance including clindamycin, triclosan, tetracyclines, and trimethoprim [14]. Recent studies have described smr (qacC) and qacA/B complexes among S. aureus isolates and suggested a link to healthcare exposure [10,15]. The quaternary ammonium compound (Qac) genes encode multidrug resistance efflux pumps that confer resistance to chlorhexidine and other antiseptic agents used in both health care procedures and as part of S. aureus decolonization protocols [16,17]. The Qac complexes are also capable of fluoroquinolone antibiotic efflux [18]. The objective of this study was to determine the clinical and molecular epidemiology of S. aureus infections among children with Down syndrome followed at Texas Children's Hospital. We hypothesized that Down syndrome patients would be overrepresented in our surveillance study because of their susceptibility to infections and we hypothesized that their S. aureus isolates would carry a higher frequency of antibiotic resistance markers compared to what has been reported for children with community acquired infections. 2. Patients and methods 2.1. Patients and isolates This was a retrospective study of patients with Down syndrome who were treated at TCH for a S. aureus infection during a ten year period (October 24, 2001eOctober 24, 2011). Since 2001, children with a documented infection caused by S. aureus have prospectively had information pertaining to their infection and hospital course entered into an ongoing surveillance study database in the Infectious Disease Research Laboratory at TCH [19]. The corresponding clinical isolates were collected from the Clinical Microbiology Laboratory at TCH and stored frozen at 80 C in defibrinated horse blood (Cocolico, Reamstown, PA). For this study, the subset of patients with Down syndrome was identified from the surveillance database. The medical records for all patients were reviewed and clinical information was recorded on a standard data collection form. This study was approved by the institutional review board at Baylor College of Medicine. 2.2. Definitions Infections in patients with Down syndrome were classified as community onset healthcare associated (CO-HCA) because of the potentially frequent healthcare contact [20,21]. Infections that occurred after 48 h of hospitalization, where no clinical evidence suggested it was present within 48 h of admission were categorized as hospital acquired infections. Community acquired (CA) infections were infections identified within 48 h of admission, or evidence suggested the infection was present upon admission (eg. osteomyelitis). Invasive S. aureus infection was defined by the isolation of S. aureus from a normally sterile body site. 2.3. Laboratory methods Antibiotic susceptibilities to clindamycin, doxycycline, ertythromycin, gentamicin, oxacillin, penicillin, and trimethoprimsulfamethaxazole (TMP-SMX) were determined on all isolates in the Clinical Microbiology Laboratory at Texas Children's Hospital as part of routine patient care. Antimicrobial susceptibilities were measured by disk diffusion methods using Clinical Laboratory Standards Institute (CLSI) methods and interpretation guidelines [22]. The D-test was performed on all strains to determine inducible macrolide-lincosamide-streptogramin B (MSLB) resistance.
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Ciprofloxacin resistance was determined on the 27 available initial and recurrent isolates in the Infectious Disease research laboratory at TCH using disk diffusion [10]. At the time of analysis, isolates were grown on tryptic soy agar plates containing 5% sheep blood. (BBL, Beckton Dickinson, Cockneysville, MD) The isolates were typed by pulsed field gel electrophoresis (PFGE) using standard methods [21]. Relationships between strains were determined based on previously published criteria [23]. Polymerase chain reaction (PCR) was performed using preexisting protocols to detect presence of the PVL toxin genes, lukSF-PV, the quaternary ammonium compound efflux pump gene smr [24], and the mupA gene conferring high-level mupirocin resistance [25]. The staphylococcal cassette chromosome mec (SCCmec) type was also characterized by PCR [21]. 2.4. Statistical analysis Patients were grouped by their S. aureus isolate (MRSA vs methicillin susceptible S. aureus, MSSA) and by clinical presentation (skin and soft tissue infection (SSTI), vs invasive infection, vs ear infection). Continuous variables were compared using KolmogoroveSmirnov test for non-parametric data. Fisher's exact test was performed for categorical variables. Statistical analyses were done using STATA11 software (Labcorp, College Station, TX). All analyses were 2-tailed and a p value of <0.05 was considered statistically significant. 3. Results 3.1. Study population Twenty-six Down syndrome patients with S. aureus infections from October 24, 2001, to October 24, 2011, met the inclusion criteria (Table 1). The majority of the patients (15/26, 57.7%) were female. The median age at time of infection was 2.6 years (range 0.1e15.6 years). Six patients had a total of eight recurrent episodes; therefore a total of 34 episodes were included in the study. The 26 episodes pertaining to initial infections were analyzed in the main study of clinical characteristics, and data pertaining to recurrent infections were analyzed separately. S. aureus isolates from 27 of 34 episodes were available for study, seven of which were from recurrent infections. All Down syndrome children presented with multiple comorbid conditions present prior to the development of S. aureus disease. Twenty (76.9%) patients had a history of sinusitis or otitis media, often with recurrences; seven presented with a S. aureus ear infection in this study. Fourteen (53.8%) patients had a history of congenital heart disease; 10 had undergone surgical corrections. Eight (30.8%) patients had a history of asthma. Four (15.4%) patients had a history of duodenal atresia. Three (11.5%) patients had a history of hypothyroidism. Two (7.7%) patients had a previous diagnosis of Hirschsprung's disease, and another two (7.7%) had a seizure disorder. One patient with a seizure disorder also had cerebral palsy and severe scoliosis. 3.2. Analysis of clinical characteristics The majority of infections were considered community onset health care associated (22/26, 84.6%), and the remaining four (15.4%) were hospital acquired infections (Table 2). The most common infectious diagnosis was a skin and soft tissue infection (SSTI) (17/26, 65.4%). Seven (26.9%) cultures were from ear infections. Osteomyelitis occurred in one case and one patient had a catheter-related blood stream infection. No
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Table 1 Demographics and clinical characteristics of patients with Down syndrome and initial S. aureus infections. All patients (n ¼ 26)
Age (yrs) Median Range Gender, n (%) Male Race, n (%) Asian Black Caucasian Hispanic Skin and soft tissue infection Ear infection Invasive infection Inpatient Hospital acquired infection Treatment with oral antibiotic Treatment with otic antibiotic Treatment with IV or IM antibiotice Antibiotics 2 weeks prior to infection Co-pathogens on culture Surgical intervention Clindamycin non-susceptible Erythromycin non-susceptible TMP/SMX non-susceptible Tetracycline or doxycycline non-susceptible Gentamicin non-susceptible a b c d e
All isolates (n ¼ 20)
MRSA n ¼ 16, (%)
MSSA n ¼ 10, (%)
Pa
USA300 n ¼ 13, (%)
Other n ¼ 7, (%)
P
3.5 (0.2e15.6)
1.1 (0.1e8.3)
0.1
4.8 (0.4e15.6)
4.4 (0.1e11.4)
0.2
7 (43.8)
4 (40)
1.0
6 (46.2)
3 (42.9)
1.0
1 (6.3) 1 (6.3) 7 (43.8) 7 (43.8) 11 (68.8) 5 (31.3) 0 11 (68.8) 2 (12.5) 10 (71.4)c 5 (31.3) 7 (50)c 7 (46.7)b 3 (18.8) 10 (66.7)b 4 (25) 15 (93.8) 0 1 (6.3) 0
0 1 6 3 6 2 2 6 2 1 1 7 0 5 7 3 7 0 0 0
0.9
0 2 (15.4) 5 (38.5) 6 (46.2) 10 (76.9) 3 (23.1) 0 9 (69.2) 2 (15.4) 7 (70)d 3 (23.1) 8 (72.7)c 5 (45.5)c 3 (23.1) 7 (58.3)b 1 (7.7) 12 (92.3) 0 0 0
1 0 4 2 3 3 1 3 0 2 3 3 2 2 5 5 5 0 1 0
0.4
(10) (60) (30) (60) (20) (20) (60) (20) (12.5)c (10) (70) (50) (70) (30) (70)
0.7 0.7 0.1 0.9 0.6 0.02 0.4 0.4 0.05 0.2 1.0 1.0 0.3 ND 1.0 ND
(14.3) (57.1) (28.6) (42.9) (42.9) (14.3) (42.9) (28.6) (42.9) (42.9) (28.6) (28.6) (71.4) (71.4) (71.4) (14.3)
0.2 0.6 0.4 0.4 1.0 0.2 0.6 0.3 1 1.0 0.7 0.007 0.3 ND 0.4 ND
Fisher's exact test was used comparing categorical variables. KolmogoroveSmirnov test was used comparing continuous variables. One datapoint missing. Two datapoints missing. Three datapoints missing. IM-intramuscular, IV-intravenous.
differences were observed between disease presentations relating to strain type characteristics, methicillin susceptibility or recurrent infections (Table 2). Down syndrome patients represented 16.8/ 10,000 (0.17%) of the total number of the patients with a community onset S. aureus infection in the surveillance study within this time period. The invasive disease prevalence was not different from the proportion of invasive disease among all community onset infections in the S. aureus surveillance database during the same time period (2/26, 7.7% vs. 1305/20,222, 6.5%, p ¼ 0.7). However, 6/26 (23%) were ear infections compared to 399/20,222 (2%) in the overall database (P < 0.0001). Fifteen of 17 initial cases of SSTIs were hospitalized; in 3 cases children were admitted for comorbid conditions and acquired an infection in the hospital. Excluding the nosocomial infections, the median length of hospitalization was 3 days (range 1e29 days). Ten SSTI (58.8%) cases required surgical incision and debridement in the operating room, four (23.5%) cases were managed with antibiotic therapy alone, and three (17.6%)
Table 2 Comparison of Skin and Soft Tissue, Otic, and Invasive S. aureus Isolates from patients with Down syndrome.
MSSA MRSA USA300 Non-USA300 PVL genesþ mupAþ smrþ Recurrences
Totala n ¼ 20 (%)
SSTI n ¼ 13 (%)
Otic n ¼ 6 (%)
Systemic n ¼ 1 (%)
P
6 (30) 14 (70) 13 (65) 7 (35) 14 (70) 5 (25) 8 (40) 0
4 (30.8) 9 (69.2) 10 (76.9) 3 (23.1) 11 (84.6) 2 (15.4) 5 (38.5) 2
1 5 3 3 3 3 3 4
1 0 0 1 0 0 0 0
0.23
(16.7) (83.3) (50) (50) (50) (50) (50)
(100) (0) (0) (100) (0) (0) (0)
0.2 0.11 0.34 1.0
a Isolates were unavailable from 4 skin and soft tissue (SSTI), 1 ear and 1 blood stream infection, respectively.
cases received an incision and drainage procedure followed by antibiotic therapy. Inpatient SSTIs were treated with antibiotics at the discretion of the treating physician. Four patients had failed outpatient treatment with oral antibiotics within two weeks prior to hospital admission. Of the outpatient failures, two patients received TMP-SMX and one received TMP-SMX and clindamycin for SSTI; the patients' S. aureus isolates upon admission were susceptible for these drugs. One patient received erythromycin for a developing decubitus ulcer; this patient had an erythromycin resistant isolate isolated upon admission. All seven cases of S. aureus isolated from outer or middle ear fluid were managed on an outpatient basis, and had a history of chronic ear and sinus problems. Three (11.5%) cultures were isolated from purulent otorrhea in the external canal and four (15.4%) were isolated intraoperatively from middle ear fluid. Isolates from ear fluid were commonly polymicrobial (5/7, 71.4%), with the most common copathogen being Streptococcus pneumoniae. Two patients received ciprofloxacin ototopical medications within the two weeks prior to a positive culture, and one patient had received ciprofloxacin ototopical medication within 6 months prior. Four of the patients had ear tubes at the time of presentation. The ear tubes were removed in one patient, replaced in two patients and cleaned in one patient. Tubes were placed in 2 patients without previous ear tubes. Six patients received oral antibiotics (trimethoprimsulfamethoxazole [n ¼ 3], clindamycin, amoxicillin-clavulanic acid or cefdinir); all patients were prescribed otic drops (ciprofloxacin/ dexamethasone [n ¼ 6] or acetic acid). The two cases of invasive infection (osteomyelitis and bacteremia) both involved premature infants with severe congenital heart disease, and occurred within the first year of life. Both cases incurred prolonged hospitalizations secondary to comorbid conditions. Both infections were polymicrobial. Citrobacter freundii was
J.N. Johnston et al. / J Infect Chemother 21 (2015) 790e794
isolated from the foot of the patient with osteomyelitis, and Enterobacter cloacae was isolated from blood cultures from the patient's peripherally inserted central catheter (PICC) in addition to S. aureus.
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available for study contained smr, were ciprofloxacin nonsusceptible and the patients associated with the recurrent infections were managed with ciprofloxacin otic drops; one patient had a recurrent infection 13 months later (after the completion of this study).
3.3. Molecular analysis by PFGE and PCR methods 4. Discussion Out of the 26 initial infections, 16 (61.5%) were MRSA and 10 (38.5%) were MSSA. Twenty isolates (14 MRSA, 6 MSSA) from initial infections were analyzed by molecular methods. Out of these 20 isolates, 13 (65%) were USA300 as determined by PFGE (11 MRSA, 2 MSSA). Ten of 13 USA300 strains caused SSTI, the remaining three manifested as ear infections. No differences in clinical features were observed when comparing MRSA and MSSA infections. Eleven of 14 (78.6%) isolates carrying PVL toxin genes manifested as a SSTI (P ¼ 0.11) and 12 of 14 isolates with PVL genes were USA300 strains. SCCmec type was determined for all available MRSA isolates. Out of 14 initial MRSA isolates, 13 (92.9%) contained SCCmec type IV (11 USA300, 2 non-USA300). One non-USA300 isolate obtained from an ear infection carried SCCmec type II. Prevalence of smr was determined by PCR and compared to ciprofloxacin resistance. Eight (40%) out of the 20 isolates from initial infections were smr positive. Five (25%) isolates were ciprofloxacin resistant, and three of those five tested positive for smr genes. Upon review of the medical record, four patients with smr positive isolates had been exposed to a fluoroquinolone antibiotic and two had undergone a surgical procedure with likely exposure to chlorhexidine in the six months prior to the positive S. aureus culture. Five isolates carried the mupA genes. All isolates which carried mupA genes also contained smr genes (P ¼ 0.004). Three (60%) mupA isolates were non-susceptible to clindamycin, and all three occurred in ear infections. 3.4. Antibiotic susceptibilities All 26 isolates were susceptible to gentamicin and TMP-SMX (Table 1). Six (23.9%) of the initial infections were clindamycin non-susceptible, 4 of which were MRSA. Two MRSA and 2 MSSA were inducibly resistant. Clindamycin non-susceptibility was associated with non-USA300 PFGE profiles (p ¼ 0.007). Three clindamycin non-susceptible isolates also contained mupA genes. 3.5. Recurrences Six patients had a total of eight recurrent infections (7 MRSA, 1 MSSA). Patients experienced between one and two recurrences within the study period occurring from three months to 3.5 years after the initial infection. Five recurrences were ear infections (3 chronic external canal otorrhea, 2 otitis media); three were from patients with tubes in place. Tube removal was performed in one patient, replaced in one patient and cleaned in one patient. All five patients were managed as outpatients and had received ciprofloxacin otic drops. Two recurrent SSTI were treated with incision and drainage procedures and subsequently managed with oral antibiotics on an outpatient basis. The MSSA osteomyelitis initial infection developed into a scar contracture which was surgically repaired three and a half years after the initial S. aureus isolation, MSSA grew from debrided soft tissue specimen. However, the initial and the recurrent isolates were not identical by PFGE. Four (50%) of eight isolates were clindamycin non-susceptible (2 inducibly resistant MRSA), and three of the clindamycin nonsusceptible isolates had identical antibiograms. Of 7 isolates available for study, three were USA300. Five isolates causing recurrent infections (71.4%) contained PVL genes, 5 contained smr, and 4 carried mupA. All four recurrent ear isolates
S. aureus is a common cause of healthcare associated infections. Children with Down syndrome have numerous anatomic and physiologic defects which place them at increased risk of infections [26e29]. One recent study by Pelton et al. reported an 8-fold rate ratio of pneumococcal pneumonia among pediatric patients with Down syndrome (trisomy 21) compared to children with no at-risk conditions [30]. The present study identified 26 patients with Down syndrome and a S. aureus infection within a 10-year period. Down syndrome patients represented 16.8/10,000 (0.17%) of the total number of patients with a community onset S. aureus infection in the surveillance study within this time period. National estimates of Down syndrome prevalence differ somewhat between studies; a prevalence of 13.51/10,000 live births was reported by Parker et al. [1] Comparison of the prevalence of Down syndrome patients in the general population to the prevalence of Down syndrome patients in the S. aureus surveillance study, suggests some over representation of these patients among patients with S. aureus infections. SSTI was the most common S. aureus diagnosis observed in this study with 88.2% of cases admitted into the hospital with a mean hospitalization of 5.4 days. Nearly 60% of SSTIs among patients with Down syndrome required surgical intervention in the operating room. In contrast, hospitalization rates among all patients with CA or CO-HCA S. aureus SSTI was approximately 50% within this time period (data not shown). The reason for the increased frequency and duration of hospitalization for SSTI compared to other population studies [19,31] could not be teased out from this study but may in part be related to the clinical management of Down syndrome patients. As expected for the Down syndrome population, a portion of the S. aureus isolates were obtained from ear fluid and associated with chronic ear infections, a condition known to afflict the Down syndrome population [32]. The frequent use of antimicrobial otic drops in the management of the ear symptoms observed led to further evaluation of ciprofloxacin use, ciprofloxacin susceptibility, and the presence of the smr gene in the isolates of the study population. Overall, the study revealed that 48% of isolates from the Down syndrome population contained smr. In comparison, a previous study of 800 blood stream infectious isolates from unspecified patient populations within and outside of the United States, including isolates from Houston, TX, reported a prevalence ranging between 2.1 and 22% depending on the geographic site. In this study, the Houston isolates were associated with the highest smr prevalence [17]. Isolates carrying smr were more likely to demonstrate ciprofloxacin non-susceptibility and more likely to be derived from patients with previous exposure to ciprofloxacin ototopical medications. This finding is in line with other studies which reported high rates of ciprofloxacin non-susceptibility in MRSA isolated from otorrhea following tympanostomy tube placement and indicates a consideration for alternative treatments [33]. The molecular analysis of Down syndrome isolates was comparable to previous observations in pediatric populations with S. aureus infections in that the majority of isolates was USA300MRSA, and carried the PVL genes and the SCCmec type IV. USA300 has previously been linked to SSTI and invasive infections. In this study 4/10 available ear isolates (9 MRSA) were also USA300.
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Clindamycin non-susceptibility was greater among non-USA300 isolates (p ¼ 0.007) and 62.5% of recurrent isolates versus 26.9% of initial isolates were clindamycin non-susceptible (p ¼ 0.1). The mupA gene conferring mupirocin resistance was identified in 25% of the initial isolates and in 50% of the recurrent infections and was associated with clindamycin non-susceptibility. While the S. aureus infections among the Down syndrome population shared many common features with other pediatric populations, antimicrobial and molecular data suggest the Down syndrome patient isolates carry more resistance markers, possibly as a result of frequent antibiotic use. Knowledge of the antimicrobial susceptibility profiles for specific patient populations such as this may help guide the empiric antibiotic choices while awaiting antimicrobial susceptibility results. Study limitations included the study population which was exclusively from Texas Children's Hospital, and thus the results may not be reflective of other regions. The small numbers of patients limit the analyses and conclusions and, as with most retrospective studies, some data were unavailable. The ear drainage cultures were polymicrobial and a S. aureus isolate from this type of specimen could be skin contaminant. Furthermore, the many comorbidities associated with Down syndrome increases the prevalence of regular antibiotic use in this population. Regular antibiotic use could potentially hinder the cultivation of a bacterial cause of infection and result in an underrepresentation of S. aureus infections for this patient group. In summary, S. aureus infections in the Down syndrome population are mostly manifesting as SSTIs. For children with ear infections, the use of ciprofloxacin otic drops was associated with smr positive and ciprofloxacin non-susceptible MRSA strains and recurrent or persistent infection. Indeed, the role of fluoroquinolone otic drop usage in the development of ciprofloxacin non-susceptible S. aureus and recurrent ear infections should be further investigated. Conflicts of interest None of the other contributing authors have any relevant financial conflicts of interest. Acknowledgments This work was supported in part by an investigator-initiated grant from Pfizer Pharmaceuticals (SLK). Pfizer was not involved with the design or conduct of the study, collection, management, analysis, or interpretation of the data, nor with the preparation, review, or approval of the manuscript. References [1] Parker SE, Mai CT, Canfield MA, Rickard R, Wang Y, Meyer RE, et al. Updated national birth prevalence estimates for selected birth defects in the United States, 2004e2006. Birth Defects Res A Clin Mol Teratol 2010;88:1008e16. [2] Summar K, Lee B. Down syndrome and other abnormalities of chromosome number. In: Kliegman RM, Stanton BF, St Geme JW, Schor NF, Behrman RE, editors. Nelson textbook of pediatrics. Philadelphia: Saunders Elsevier Inc.; 2011. p. 399e404. [3] Gordon RJ, Lowy FD. Pathogenesis of methicillin-resistant Staphylococcus aureus infection. Clin Infect Dis 2008;46:S350e9. [4] Kaplan SL. Community-acquired methicillin-resistant Staphylococcus aureus infections in children. Semin Pediatr Infect Dis 2006;17:113e9. [5] Bocchini CE, Hulten KG, Mason Jr EO, Gonzalez BE, Hammerman WA, Kaplan SL. Panton-Valentine leukocidin genes are associated with enhanced inflammatory response and local disease in acute hematogenous Staphylococcus aureus osteomyelitis in children. Pediatrics 2006;117:433e40. [6] Diekema DJ, Richter SS, Heilmann KP, Dohrn CL, Riahi F, Tendolkar S, et al. Continued emergence of USA300 methicillin-resistant Staphylococcus aureus in the United States: results from a nationwide surveillance study. Infect Control Hosp Epidemiol 2014;35:285e92.
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[19] Kaplan SL, Hulten KG, Gonzalez BE, Hammerman WA, Lamberth L, Versalovic J, et al. Three-year surveillance of community-acquired Staphylococcus aureus infections in children. Clin Infect Dis 2005;40:1785e91. [20] Naimi TS, LeDell KH, Como-Sabetti K, Borchardt SM, Boxrud DJ, Etienne J, et al. Comparison of community- and health care-associated methicillin-resistant Staphylococcus aureus infection. J Am Med Assoc 2003;290:2976e84. [21] Hulten KG, Kaplan SL, Gonzalez BE, Hammerman WA, Lamberth LB, Versalovic J, et al. Three-year surveillance of community onset health careassociated Staphylococcus aureus infections in children. Pediatr Infect Dis J 2006;25:349e53. [22] Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing. 20th informational supplement M100eS20. Wayne, PA: Clinical and Laboratory Standards Institute; 2012. [23] Tenover FC, Arbeit RD, Goering RV, Mickelsen PA, Murray BE, Persing DH. Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J Clin Microbiol 1995;33:2233e9. [24] Noguchi N, Hase M, Kitta M, Sasatsu M, Deguchi K, Kono M. Antiseptic susceptibility and distribution of antiseptic-resistance genes in methicillinresistant Staphylococcus aureus. FEMS Microbiol Lett 1999;172:247e53. [25] Diep BA, Chambers HF, Graber CJ, Szumowski JD, Miller LG, Han LL, et al. Emergence of multidrug-resistant, community-associated, methicillinresistant Staphylococcus aureus clone USA300 in men who have sex with men. Ann Intern Med 2008;148:249e57. [26] Ram G, Chinen J. Infections and immunodeficiency in Down syndrome. Clin Exp Immunol 2011;164:9e16. [27] Baird PA, Sadovnick AD. Underlying causes of death in Down syndrome: accuracy of British Columbia death certificate data. Can J Public Health 1990;81: 456e61. [28] Nespoli L, Burgio GR, Ugazio AG, Maccario R. Immunological features of down's syndrome: a review. J Intellect Disabil Res 1993;37:543e51. [29] Baird PA, Sadovnick AD. Causes of death to age 30 in Down syndrome. Am J Hum Genet 1988;43:239e48. [30] Pelton SI, Weycker D, Farkouh RA, Strutton DR, Shea KM, Edelsberg J. Risk of pneumococcal disease in children with chronic medical conditions in the era of pneumococcal conjugate vaccine. Clin Infect Dis 2014;59:615e23. [31] Teran CG, Sura S, Thant Lin TM, Medows M, Cynthia D, Wong SH. Current role of community-acquired methicillin-resistant Staphylococcus aureus among children with skin and soft tissue infections. Pediatr Rep 2012;4:e5. [32] Kanamori G, Witter M, Brown J, Williams-Smith L. Otolaryngologic manifestations of Down syndrome. Otolaryngol Clin North Am 2000;33:1285e92. [33] Hartnick CJ, Shott S, Willging JP, Myer III CM. Methicillin-resistant Staphylococcus aureus otorrhea after tympanostomy tube placement: an emerging concern. Arch Otolaryngol Head Neck Surg 2000;126:1440e3.
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Original article
Characterization of Staphylococcus aureus infections in children with Down syndrome Jeffrey N. Johnston, Sheldon L. Kaplan, Edward O. Mason, Kristina G. Hulten* Texas Children's Hospital, Department of Pediatrics, Section of Infectious Diseases, Baylor College of Medicine, Houston, TX, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 April 2015 Received in revised form 3 August 2015 Accepted 4 August 2015 Available online 18 September 2015
Staphylococcus aureus infections in the Down syndrome (DS) population have not been well characterized. This study determined clinical and molecular characteristics of S. aureus infections in children with DS followed at Texas Children's Hospital (TCH), from 2001 to 2011. Patients were retrospectively identified from an ongoing S. aureus surveillance study. Medical records were reviewed. Isolates were characterized by antimicrobial susceptibility, pulsed-field gel electrophoresis patterns, and detection of PVL genes (pvl), mupA (high-level mupirocin resistance gene), smr (chlorhexidine resistance conferring gene), and Staphylococcal Chromosomal Cassette mec (SCCmec) type. Twenty-six patients with DS had a total of 34 S. aureus infections (8 recurrent); 61% were MRSA. DS patients represented 16.8 per 10,000 community onset S. aureus infections seen at TCH. Among 26 initial infections 17 were skin and soft tissue (SSTI), 7 were outer or middle ear and 2 were invasive infections. Seventeen patients were hospitalized. Thirteen (65%) of 20 available isolates were USA300, 14 were pvlþ, 5 were mupAþ, and 8 were smrþ. Five of 8 (63%) recurrent infections were ear infections. All 4 recurrent ear isolates available for study were smrþ, ciprofloxacin non-susceptible and treated with ciprofloxacin otic drops. S. aureus infections among patients with DS were similar in presentation to other patient groups, except for a greater proportion being associated with ear infections. Seventy percent of ear fluid isolates carried antiseptic and fluoroquinolone resistance genes. A study of a greater number of DS patients is warranted to further explore these findings. © 2015, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
Keywords: Staphylococcus aureus Down syndrome Pediatric smr mupA
1. Introduction Down syndrome is the most common chromosomal abnormality of live births. The prevalence of Down syndrome has been steadily increasing in the United States and currently affects one in 740 live births, or 13.51/10,000 live births [1]. Children with Down syndrome frequently require medical care for a variety of problems, including more frequent infections; a result of both immunological and anatomical factors. The altered upper airway anatomy increases the risk of Eustachian tube dysfunction and likely plays a role in chronic and recurrent otitis media as well as other upper respiratory tract infections [2]. Atopic dermatitis and skin infections are also common.
* Corresponding author. 1102 Bates St. Suite 1150, Houston, TX, 77030, United States. Tel.: þ1 832 824 4325; fax: þ1 832 825 4347. E-mail address: [email protected] (K.G. Hulten).
Staphylococcus aureus infections are common in the general pediatric population in the United States; no study has described the clinical spectrum and epidemiology of these infections in the Down syndrome patient population. In the United States, the most common community acquired strain, USA300, is associated with the cytotoxin Panton-Valentine leukocidin (PVL) and increased rates of complications in otherwise healthy individuals [3e7]. USA300 methicillin resistant S. aureus (MRSA) isolates carry the 21e25 kb Staphylococcal Cassette Chromsome mec (SCCmec) IV, incurring resistance to beta-lactam antibiotics, while frequently remaining susceptible to many non-beta lactam antibiotics [8]. Exposure to the healthcare setting, medical interventions and use of antibiotics are risk factors in acquiring infections with bacterial strains carrying antibiotic resistance markers [9]. Among these, genes conferring resistance to mupirocin or chlorhexidine have been reported to increase in prevalence among S. aureus isolates [10e12]. The mupA gene is commonly plasmid mediated, confers high-level resistance to mupirocin and has been linked to
http://dx.doi.org/10.1016/j.jiac.2015.08.002 1341-321X/© 2015, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
J.N. Johnston et al. / J Infect Chemother 21 (2015) 790e794
decreased efficacy of nasal decolonization protocols [13]. mupA positive S. aureus strains have been associated with additional antimicrobial resistance including clindamycin, triclosan, tetracyclines, and trimethoprim [14]. Recent studies have described smr (qacC) and qacA/B complexes among S. aureus isolates and suggested a link to healthcare exposure [10,15]. The quaternary ammonium compound (Qac) genes encode multidrug resistance efflux pumps that confer resistance to chlorhexidine and other antiseptic agents used in both health care procedures and as part of S. aureus decolonization protocols [16,17]. The Qac complexes are also capable of fluoroquinolone antibiotic efflux [18]. The objective of this study was to determine the clinical and molecular epidemiology of S. aureus infections among children with Down syndrome followed at Texas Children's Hospital. We hypothesized that Down syndrome patients would be overrepresented in our surveillance study because of their susceptibility to infections and we hypothesized that their S. aureus isolates would carry a higher frequency of antibiotic resistance markers compared to what has been reported for children with community acquired infections. 2. Patients and methods 2.1. Patients and isolates This was a retrospective study of patients with Down syndrome who were treated at TCH for a S. aureus infection during a ten year period (October 24, 2001eOctober 24, 2011). Since 2001, children with a documented infection caused by S. aureus have prospectively had information pertaining to their infection and hospital course entered into an ongoing surveillance study database in the Infectious Disease Research Laboratory at TCH [19]. The corresponding clinical isolates were collected from the Clinical Microbiology Laboratory at TCH and stored frozen at 80 C in defibrinated horse blood (Cocolico, Reamstown, PA). For this study, the subset of patients with Down syndrome was identified from the surveillance database. The medical records for all patients were reviewed and clinical information was recorded on a standard data collection form. This study was approved by the institutional review board at Baylor College of Medicine. 2.2. Definitions Infections in patients with Down syndrome were classified as community onset healthcare associated (CO-HCA) because of the potentially frequent healthcare contact [20,21]. Infections that occurred after 48 h of hospitalization, where no clinical evidence suggested it was present within 48 h of admission were categorized as hospital acquired infections. Community acquired (CA) infections were infections identified within 48 h of admission, or evidence suggested the infection was present upon admission (eg. osteomyelitis). Invasive S. aureus infection was defined by the isolation of S. aureus from a normally sterile body site. 2.3. Laboratory methods Antibiotic susceptibilities to clindamycin, doxycycline, ertythromycin, gentamicin, oxacillin, penicillin, and trimethoprimsulfamethaxazole (TMP-SMX) were determined on all isolates in the Clinical Microbiology Laboratory at Texas Children's Hospital as part of routine patient care. Antimicrobial susceptibilities were measured by disk diffusion methods using Clinical Laboratory Standards Institute (CLSI) methods and interpretation guidelines [22]. The D-test was performed on all strains to determine inducible macrolide-lincosamide-streptogramin B (MSLB) resistance.
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Ciprofloxacin resistance was determined on the 27 available initial and recurrent isolates in the Infectious Disease research laboratory at TCH using disk diffusion [10]. At the time of analysis, isolates were grown on tryptic soy agar plates containing 5% sheep blood. (BBL, Beckton Dickinson, Cockneysville, MD) The isolates were typed by pulsed field gel electrophoresis (PFGE) using standard methods [21]. Relationships between strains were determined based on previously published criteria [23]. Polymerase chain reaction (PCR) was performed using preexisting protocols to detect presence of the PVL toxin genes, lukSF-PV, the quaternary ammonium compound efflux pump gene smr [24], and the mupA gene conferring high-level mupirocin resistance [25]. The staphylococcal cassette chromosome mec (SCCmec) type was also characterized by PCR [21]. 2.4. Statistical analysis Patients were grouped by their S. aureus isolate (MRSA vs methicillin susceptible S. aureus, MSSA) and by clinical presentation (skin and soft tissue infection (SSTI), vs invasive infection, vs ear infection). Continuous variables were compared using KolmogoroveSmirnov test for non-parametric data. Fisher's exact test was performed for categorical variables. Statistical analyses were done using STATA11 software (Labcorp, College Station, TX). All analyses were 2-tailed and a p value of <0.05 was considered statistically significant. 3. Results 3.1. Study population Twenty-six Down syndrome patients with S. aureus infections from October 24, 2001, to October 24, 2011, met the inclusion criteria (Table 1). The majority of the patients (15/26, 57.7%) were female. The median age at time of infection was 2.6 years (range 0.1e15.6 years). Six patients had a total of eight recurrent episodes; therefore a total of 34 episodes were included in the study. The 26 episodes pertaining to initial infections were analyzed in the main study of clinical characteristics, and data pertaining to recurrent infections were analyzed separately. S. aureus isolates from 27 of 34 episodes were available for study, seven of which were from recurrent infections. All Down syndrome children presented with multiple comorbid conditions present prior to the development of S. aureus disease. Twenty (76.9%) patients had a history of sinusitis or otitis media, often with recurrences; seven presented with a S. aureus ear infection in this study. Fourteen (53.8%) patients had a history of congenital heart disease; 10 had undergone surgical corrections. Eight (30.8%) patients had a history of asthma. Four (15.4%) patients had a history of duodenal atresia. Three (11.5%) patients had a history of hypothyroidism. Two (7.7%) patients had a previous diagnosis of Hirschsprung's disease, and another two (7.7%) had a seizure disorder. One patient with a seizure disorder also had cerebral palsy and severe scoliosis. 3.2. Analysis of clinical characteristics The majority of infections were considered community onset health care associated (22/26, 84.6%), and the remaining four (15.4%) were hospital acquired infections (Table 2). The most common infectious diagnosis was a skin and soft tissue infection (SSTI) (17/26, 65.4%). Seven (26.9%) cultures were from ear infections. Osteomyelitis occurred in one case and one patient had a catheter-related blood stream infection. No
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Table 1 Demographics and clinical characteristics of patients with Down syndrome and initial S. aureus infections. All patients (n ¼ 26)
Age (yrs) Median Range Gender, n (%) Male Race, n (%) Asian Black Caucasian Hispanic Skin and soft tissue infection Ear infection Invasive infection Inpatient Hospital acquired infection Treatment with oral antibiotic Treatment with otic antibiotic Treatment with IV or IM antibiotice Antibiotics 2 weeks prior to infection Co-pathogens on culture Surgical intervention Clindamycin non-susceptible Erythromycin non-susceptible TMP/SMX non-susceptible Tetracycline or doxycycline non-susceptible Gentamicin non-susceptible a b c d e
All isolates (n ¼ 20)
MRSA n ¼ 16, (%)
MSSA n ¼ 10, (%)
Pa
USA300 n ¼ 13, (%)
Other n ¼ 7, (%)
P
3.5 (0.2e15.6)
1.1 (0.1e8.3)
0.1
4.8 (0.4e15.6)
4.4 (0.1e11.4)
0.2
7 (43.8)
4 (40)
1.0
6 (46.2)
3 (42.9)
1.0
1 (6.3) 1 (6.3) 7 (43.8) 7 (43.8) 11 (68.8) 5 (31.3) 0 11 (68.8) 2 (12.5) 10 (71.4)c 5 (31.3) 7 (50)c 7 (46.7)b 3 (18.8) 10 (66.7)b 4 (25) 15 (93.8) 0 1 (6.3) 0
0 1 6 3 6 2 2 6 2 1 1 7 0 5 7 3 7 0 0 0
0.9
0 2 (15.4) 5 (38.5) 6 (46.2) 10 (76.9) 3 (23.1) 0 9 (69.2) 2 (15.4) 7 (70)d 3 (23.1) 8 (72.7)c 5 (45.5)c 3 (23.1) 7 (58.3)b 1 (7.7) 12 (92.3) 0 0 0
1 0 4 2 3 3 1 3 0 2 3 3 2 2 5 5 5 0 1 0
0.4
(10) (60) (30) (60) (20) (20) (60) (20) (12.5)c (10) (70) (50) (70) (30) (70)
0.7 0.7 0.1 0.9 0.6 0.02 0.4 0.4 0.05 0.2 1.0 1.0 0.3 ND 1.0 ND
(14.3) (57.1) (28.6) (42.9) (42.9) (14.3) (42.9) (28.6) (42.9) (42.9) (28.6) (28.6) (71.4) (71.4) (71.4) (14.3)
0.2 0.6 0.4 0.4 1.0 0.2 0.6 0.3 1 1.0 0.7 0.007 0.3 ND 0.4 ND
Fisher's exact test was used comparing categorical variables. KolmogoroveSmirnov test was used comparing continuous variables. One datapoint missing. Two datapoints missing. Three datapoints missing. IM-intramuscular, IV-intravenous.
differences were observed between disease presentations relating to strain type characteristics, methicillin susceptibility or recurrent infections (Table 2). Down syndrome patients represented 16.8/ 10,000 (0.17%) of the total number of the patients with a community onset S. aureus infection in the surveillance study within this time period. The invasive disease prevalence was not different from the proportion of invasive disease among all community onset infections in the S. aureus surveillance database during the same time period (2/26, 7.7% vs. 1305/20,222, 6.5%, p ¼ 0.7). However, 6/26 (23%) were ear infections compared to 399/20,222 (2%) in the overall database (P < 0.0001). Fifteen of 17 initial cases of SSTIs were hospitalized; in 3 cases children were admitted for comorbid conditions and acquired an infection in the hospital. Excluding the nosocomial infections, the median length of hospitalization was 3 days (range 1e29 days). Ten SSTI (58.8%) cases required surgical incision and debridement in the operating room, four (23.5%) cases were managed with antibiotic therapy alone, and three (17.6%)
Table 2 Comparison of Skin and Soft Tissue, Otic, and Invasive S. aureus Isolates from patients with Down syndrome.
MSSA MRSA USA300 Non-USA300 PVL genesþ mupAþ smrþ Recurrences
Totala n ¼ 20 (%)
SSTI n ¼ 13 (%)
Otic n ¼ 6 (%)
Systemic n ¼ 1 (%)
P
6 (30) 14 (70) 13 (65) 7 (35) 14 (70) 5 (25) 8 (40) 0
4 (30.8) 9 (69.2) 10 (76.9) 3 (23.1) 11 (84.6) 2 (15.4) 5 (38.5) 2
1 5 3 3 3 3 3 4
1 0 0 1 0 0 0 0
0.23
(16.7) (83.3) (50) (50) (50) (50) (50)
(100) (0) (0) (100) (0) (0) (0)
0.2 0.11 0.34 1.0
a Isolates were unavailable from 4 skin and soft tissue (SSTI), 1 ear and 1 blood stream infection, respectively.
cases received an incision and drainage procedure followed by antibiotic therapy. Inpatient SSTIs were treated with antibiotics at the discretion of the treating physician. Four patients had failed outpatient treatment with oral antibiotics within two weeks prior to hospital admission. Of the outpatient failures, two patients received TMP-SMX and one received TMP-SMX and clindamycin for SSTI; the patients' S. aureus isolates upon admission were susceptible for these drugs. One patient received erythromycin for a developing decubitus ulcer; this patient had an erythromycin resistant isolate isolated upon admission. All seven cases of S. aureus isolated from outer or middle ear fluid were managed on an outpatient basis, and had a history of chronic ear and sinus problems. Three (11.5%) cultures were isolated from purulent otorrhea in the external canal and four (15.4%) were isolated intraoperatively from middle ear fluid. Isolates from ear fluid were commonly polymicrobial (5/7, 71.4%), with the most common copathogen being Streptococcus pneumoniae. Two patients received ciprofloxacin ototopical medications within the two weeks prior to a positive culture, and one patient had received ciprofloxacin ototopical medication within 6 months prior. Four of the patients had ear tubes at the time of presentation. The ear tubes were removed in one patient, replaced in two patients and cleaned in one patient. Tubes were placed in 2 patients without previous ear tubes. Six patients received oral antibiotics (trimethoprimsulfamethoxazole [n ¼ 3], clindamycin, amoxicillin-clavulanic acid or cefdinir); all patients were prescribed otic drops (ciprofloxacin/ dexamethasone [n ¼ 6] or acetic acid). The two cases of invasive infection (osteomyelitis and bacteremia) both involved premature infants with severe congenital heart disease, and occurred within the first year of life. Both cases incurred prolonged hospitalizations secondary to comorbid conditions. Both infections were polymicrobial. Citrobacter freundii was
J.N. Johnston et al. / J Infect Chemother 21 (2015) 790e794
isolated from the foot of the patient with osteomyelitis, and Enterobacter cloacae was isolated from blood cultures from the patient's peripherally inserted central catheter (PICC) in addition to S. aureus.
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available for study contained smr, were ciprofloxacin nonsusceptible and the patients associated with the recurrent infections were managed with ciprofloxacin otic drops; one patient had a recurrent infection 13 months later (after the completion of this study).
3.3. Molecular analysis by PFGE and PCR methods 4. Discussion Out of the 26 initial infections, 16 (61.5%) were MRSA and 10 (38.5%) were MSSA. Twenty isolates (14 MRSA, 6 MSSA) from initial infections were analyzed by molecular methods. Out of these 20 isolates, 13 (65%) were USA300 as determined by PFGE (11 MRSA, 2 MSSA). Ten of 13 USA300 strains caused SSTI, the remaining three manifested as ear infections. No differences in clinical features were observed when comparing MRSA and MSSA infections. Eleven of 14 (78.6%) isolates carrying PVL toxin genes manifested as a SSTI (P ¼ 0.11) and 12 of 14 isolates with PVL genes were USA300 strains. SCCmec type was determined for all available MRSA isolates. Out of 14 initial MRSA isolates, 13 (92.9%) contained SCCmec type IV (11 USA300, 2 non-USA300). One non-USA300 isolate obtained from an ear infection carried SCCmec type II. Prevalence of smr was determined by PCR and compared to ciprofloxacin resistance. Eight (40%) out of the 20 isolates from initial infections were smr positive. Five (25%) isolates were ciprofloxacin resistant, and three of those five tested positive for smr genes. Upon review of the medical record, four patients with smr positive isolates had been exposed to a fluoroquinolone antibiotic and two had undergone a surgical procedure with likely exposure to chlorhexidine in the six months prior to the positive S. aureus culture. Five isolates carried the mupA genes. All isolates which carried mupA genes also contained smr genes (P ¼ 0.004). Three (60%) mupA isolates were non-susceptible to clindamycin, and all three occurred in ear infections. 3.4. Antibiotic susceptibilities All 26 isolates were susceptible to gentamicin and TMP-SMX (Table 1). Six (23.9%) of the initial infections were clindamycin non-susceptible, 4 of which were MRSA. Two MRSA and 2 MSSA were inducibly resistant. Clindamycin non-susceptibility was associated with non-USA300 PFGE profiles (p ¼ 0.007). Three clindamycin non-susceptible isolates also contained mupA genes. 3.5. Recurrences Six patients had a total of eight recurrent infections (7 MRSA, 1 MSSA). Patients experienced between one and two recurrences within the study period occurring from three months to 3.5 years after the initial infection. Five recurrences were ear infections (3 chronic external canal otorrhea, 2 otitis media); three were from patients with tubes in place. Tube removal was performed in one patient, replaced in one patient and cleaned in one patient. All five patients were managed as outpatients and had received ciprofloxacin otic drops. Two recurrent SSTI were treated with incision and drainage procedures and subsequently managed with oral antibiotics on an outpatient basis. The MSSA osteomyelitis initial infection developed into a scar contracture which was surgically repaired three and a half years after the initial S. aureus isolation, MSSA grew from debrided soft tissue specimen. However, the initial and the recurrent isolates were not identical by PFGE. Four (50%) of eight isolates were clindamycin non-susceptible (2 inducibly resistant MRSA), and three of the clindamycin nonsusceptible isolates had identical antibiograms. Of 7 isolates available for study, three were USA300. Five isolates causing recurrent infections (71.4%) contained PVL genes, 5 contained smr, and 4 carried mupA. All four recurrent ear isolates
S. aureus is a common cause of healthcare associated infections. Children with Down syndrome have numerous anatomic and physiologic defects which place them at increased risk of infections [26e29]. One recent study by Pelton et al. reported an 8-fold rate ratio of pneumococcal pneumonia among pediatric patients with Down syndrome (trisomy 21) compared to children with no at-risk conditions [30]. The present study identified 26 patients with Down syndrome and a S. aureus infection within a 10-year period. Down syndrome patients represented 16.8/10,000 (0.17%) of the total number of patients with a community onset S. aureus infection in the surveillance study within this time period. National estimates of Down syndrome prevalence differ somewhat between studies; a prevalence of 13.51/10,000 live births was reported by Parker et al. [1] Comparison of the prevalence of Down syndrome patients in the general population to the prevalence of Down syndrome patients in the S. aureus surveillance study, suggests some over representation of these patients among patients with S. aureus infections. SSTI was the most common S. aureus diagnosis observed in this study with 88.2% of cases admitted into the hospital with a mean hospitalization of 5.4 days. Nearly 60% of SSTIs among patients with Down syndrome required surgical intervention in the operating room. In contrast, hospitalization rates among all patients with CA or CO-HCA S. aureus SSTI was approximately 50% within this time period (data not shown). The reason for the increased frequency and duration of hospitalization for SSTI compared to other population studies [19,31] could not be teased out from this study but may in part be related to the clinical management of Down syndrome patients. As expected for the Down syndrome population, a portion of the S. aureus isolates were obtained from ear fluid and associated with chronic ear infections, a condition known to afflict the Down syndrome population [32]. The frequent use of antimicrobial otic drops in the management of the ear symptoms observed led to further evaluation of ciprofloxacin use, ciprofloxacin susceptibility, and the presence of the smr gene in the isolates of the study population. Overall, the study revealed that 48% of isolates from the Down syndrome population contained smr. In comparison, a previous study of 800 blood stream infectious isolates from unspecified patient populations within and outside of the United States, including isolates from Houston, TX, reported a prevalence ranging between 2.1 and 22% depending on the geographic site. In this study, the Houston isolates were associated with the highest smr prevalence [17]. Isolates carrying smr were more likely to demonstrate ciprofloxacin non-susceptibility and more likely to be derived from patients with previous exposure to ciprofloxacin ototopical medications. This finding is in line with other studies which reported high rates of ciprofloxacin non-susceptibility in MRSA isolated from otorrhea following tympanostomy tube placement and indicates a consideration for alternative treatments [33]. The molecular analysis of Down syndrome isolates was comparable to previous observations in pediatric populations with S. aureus infections in that the majority of isolates was USA300MRSA, and carried the PVL genes and the SCCmec type IV. USA300 has previously been linked to SSTI and invasive infections. In this study 4/10 available ear isolates (9 MRSA) were also USA300.
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Clindamycin non-susceptibility was greater among non-USA300 isolates (p ¼ 0.007) and 62.5% of recurrent isolates versus 26.9% of initial isolates were clindamycin non-susceptible (p ¼ 0.1). The mupA gene conferring mupirocin resistance was identified in 25% of the initial isolates and in 50% of the recurrent infections and was associated with clindamycin non-susceptibility. While the S. aureus infections among the Down syndrome population shared many common features with other pediatric populations, antimicrobial and molecular data suggest the Down syndrome patient isolates carry more resistance markers, possibly as a result of frequent antibiotic use. Knowledge of the antimicrobial susceptibility profiles for specific patient populations such as this may help guide the empiric antibiotic choices while awaiting antimicrobial susceptibility results. Study limitations included the study population which was exclusively from Texas Children's Hospital, and thus the results may not be reflective of other regions. The small numbers of patients limit the analyses and conclusions and, as with most retrospective studies, some data were unavailable. The ear drainage cultures were polymicrobial and a S. aureus isolate from this type of specimen could be skin contaminant. Furthermore, the many comorbidities associated with Down syndrome increases the prevalence of regular antibiotic use in this population. Regular antibiotic use could potentially hinder the cultivation of a bacterial cause of infection and result in an underrepresentation of S. aureus infections for this patient group. In summary, S. aureus infections in the Down syndrome population are mostly manifesting as SSTIs. For children with ear infections, the use of ciprofloxacin otic drops was associated with smr positive and ciprofloxacin non-susceptible MRSA strains and recurrent or persistent infection. Indeed, the role of fluoroquinolone otic drop usage in the development of ciprofloxacin non-susceptible S. aureus and recurrent ear infections should be further investigated. Conflicts of interest None of the other contributing authors have any relevant financial conflicts of interest. Acknowledgments This work was supported in part by an investigator-initiated grant from Pfizer Pharmaceuticals (SLK). Pfizer was not involved with the design or conduct of the study, collection, management, analysis, or interpretation of the data, nor with the preparation, review, or approval of the manuscript. References [1] Parker SE, Mai CT, Canfield MA, Rickard R, Wang Y, Meyer RE, et al. Updated national birth prevalence estimates for selected birth defects in the United States, 2004e2006. Birth Defects Res A Clin Mol Teratol 2010;88:1008e16. [2] Summar K, Lee B. Down syndrome and other abnormalities of chromosome number. In: Kliegman RM, Stanton BF, St Geme JW, Schor NF, Behrman RE, editors. Nelson textbook of pediatrics. Philadelphia: Saunders Elsevier Inc.; 2011. p. 399e404. [3] Gordon RJ, Lowy FD. Pathogenesis of methicillin-resistant Staphylococcus aureus infection. Clin Infect Dis 2008;46:S350e9. [4] Kaplan SL. Community-acquired methicillin-resistant Staphylococcus aureus infections in children. Semin Pediatr Infect Dis 2006;17:113e9. [5] Bocchini CE, Hulten KG, Mason Jr EO, Gonzalez BE, Hammerman WA, Kaplan SL. Panton-Valentine leukocidin genes are associated with enhanced inflammatory response and local disease in acute hematogenous Staphylococcus aureus osteomyelitis in children. Pediatrics 2006;117:433e40. [6] Diekema DJ, Richter SS, Heilmann KP, Dohrn CL, Riahi F, Tendolkar S, et al. Continued emergence of USA300 methicillin-resistant Staphylococcus aureus in the United States: results from a nationwide surveillance study. Infect Control Hosp Epidemiol 2014;35:285e92.
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