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Epidemiological significance of cutaneous, pharyngeal, and digestive tract colonization by multiresistant Acinetobacter baumannii in ICU patients
rouvnal
of Hospital
Infection
(1997)
37, 287-295
Epidemiological significance of cutaneous, pharyngeal, and digestive tract colonization by multiresistant Acine tobacter baumannii in ICU patients J. Ayats,
X. Corbella *, C. Ardanuy, J. Ariza *, R. Martin
M. A. Dominguez, and J. Liiiares
A. Ricart-f-,
Departments of Microbiology, *Infectious Disease, and j-Intensive Medicine, Hospital de Bellvitge, University of Barcelona, Barcelona, Spain Received
5 March
1997;
Yevised manuscript
accepted
25 j%ne 1997
Summary:
The aim of this prospective study was to assess the relative epidemiological role of digestive tract colonization by Acinetobacter bauman&i, in comparison with other body site colonizations, in patients admitted to intensive care units (ICUs). From January to May 1995, axillary, pharyngeal and rectal swabs were taken together within the first 48 h of admission, and then weekly during ICU stay. Seventy-three patients were included, 48 of them (66%) had axillary, pharyngeal, or rectal colonization with A. baumannii, nine (19%) of these 48 during the first 48 h and the remaining 28 (77%) during the first week. Twenty-one (29%) had clinical samples positive for A. baumannii and axillary, pharyngeal, or rectal colonization. In 15 of these 21 (71%), colonization on body sites occurred prior to isolation from clinical samples (mean seven days, range l-20). Throughout admission, rates of detection of A. baumannii were 75% (36/48) for axillary or pharyngeal swabs and 77% (37/48) for rectal swabs. Combination of two bodv site swabs yielded culture‘ positive rates of 90% (43/48) for axillary-pharyngeal or axillary-rectal sites, and 96% (46/48) for pharyngeal-rectal. Two epidemic clones were defined by antibiotype and pulsed-field gel electrophoresis (PFGE) of SmaI DNA digests in 43 isolates from 11 patients. We conclude that body sites of patients were a major reservoir for A. baumannii infections in the outbreak. This finding casts doubt on the value of selective decontamination of the digestive tract as an additional infection control measure in this kind of outbreak. The weekly performance of pharyngeal and rectal swabs appears to detect A. baumannii colonization early among ICU patients and enables barrier methods to be applied rapidly. Keywords:
A.
baumannii;
epidemiology;
colonization.
Introduction
Acinetobacter baumannii has increasingly hospital outbreaks worldwide.‘-* Although
been involved as an agent of different objects in the hospital
Correspondence to: Dr. Josefina Ayats, Microbiology Department, L’Hospitalet de Llobregat, Barcelona, Spain. Fax: (34)-(3)-263.01.62. This paper was presented in part at the 36th International Conference Chemotherapy, held in iVew Orleans, Louisiana, in September 1996. 0195%6701/97/120287+09
$12.00/O
Hospital
de Bellvitge,
on Antimicrobial
0 1997 The Hospital
287
Agents
Infection
08907 and
Society
288
J. Ayats et al.
environment have been implicated as sources of infections, the major epidemiological features in large and sustained outbreaks remain, as yet, unexplained and the natural reservoir of this species ill-defined.‘-” Since the genus Acinetobacter is a normal inhabitant of human skin,12,13 several authors have postulated that patients could be a major epidemiological reservoir of A. baumannii in hospital outbreaks of infections.7Xs In agreement with others,4”4 we found a high prevalence of digestive tract colonization in our intensive care unit (ICU) population in a previous study.15 As a result, selective intestinal decontamination was proposed as an additional control measure by some.14 However, its contribution to the definitive control of this kind of outbreak is questioned by the observation that the skin and pharynx of patients could also be colonized by A. baumannii.‘“‘8 In order to provide an appropriate basis for the rational management of hospital outbreaks, we performed a prospective study to evaluate the relative epidemiological significance of digestive tract colonization in comparison with two other body sites.
Materials
and methods
Setting Hospital de Bellvitge is a lOOO-bed teaching hospital for adults in Barcelona, Spain, which provides acute medical and surgical care, excluding paediatrics, obstetrics and burns. About 23 000 patients are admitted per year, and it has three 12-bed ICUs with an active organ transplantation program. Since 1992, a significant increase in multiresistant A. baumannii isolates, susceptible only to imipenem and sulbactam, has been observed, and a specific infection control program has been introduced. From September 1994 to May 1995, the concomitant epidemic emergence was noted of a new strain of multiresistant A. baumannii with the same antibiotype, but sensitive to amikacin and ciprofloxacin.15”9 Study design The study was centred in one of the three ICUs (ICU-a), and its objectives were as follows, (1) to evaluate the relative epidemiological role of colonization of each of three body sites (axillary, pharyngeal, and digestive) by multiresistant A. baumannii; (2) to analyse the relationship between different body site colonization and clinical colonizations or infections; and (3) to assess the effectiveness of prospective surveillance of patient colonization by means of body site swabs. Axillary, pharyngeal, and rectal swabs were obtained within the first 48h after admission to ICU, and then weekly during their stay from all patients admitted from January 1 to May 31, 1995. All those patients admitted to the ICU for more than 48h, and who, in addition, had at least two series
A. baumannii
in the ICU
289
of axillary-pharyngeal-rectal swabs performed were included in the study and entered into a computer-assisted protocol. For those free of colonization with A. baumannii, a single additional series of three body site swabs performed seven days after discharge from ICU was required. Some critically ill patients coming from other hospital wards or from outside the hospital are temporally admitted for a few hours or days to a lo-bed observation unit, while waiting for ICU admission. This unit is sited in the emergency department and offers mechanical ventilation. In order to ensure that patients admitted to ICU were not previously colonized with A. baumannii, the same three body site swabs were also taken from all patients admitted to this observation unit during the study period. Clinical colonization and infection dejkitions Standard Center for Disease Control definitions were used.” Specimens obtained from axillary, pharyngeal, and rectal swabs were not considered as clinical samples. Microbiological methods Since all multiresistant A. baumannii strains isolated from clinical specimens during the outbreak were found to be gentamicin-resistant, this antibiotic was used as a selective agent for the screening of samples. Swabs were plated on MacConkey agar, supplemented with 6 pg/mL gentamicin, and on 5% sheep blood agar plates. The plates were incubated aerobically at 37°C for 48h. Isolates were identified as A. baumannii using standard biochemical reactions in a MicroScanTM system (Baxter Diagnostics Inc., West Sacramento, USA), and by their ability to grow at 44°C. Antibiotic susceptibility was performed by a microdilution method in the same system (Baxter). The strains were classified for resistance according to NCCLS criteria.21 Pulsed-field gel electrophoresis (PFGE) was performed for 43 multiresistant A. baumannii strains isolated during the study period in clinical (N=8) and colonized (N=35) samples from 11 patients. Genomic DNA was prepared in agarose plugs as previously described.22 DNA inserts were digested with the endonuclease SmaI according to the manufacturer’s specifications (New England BioLabs, Beverly, MA, USA). DNA restriction fragments were separated by PFGE, using a CHEF-DR III apparatus (Bio-Rad, Hercules, CA, USA). The conditions for electrophoresis were 200 V for 20h, with pulse times ranging from 0.5-l 5 s. Isolates were assigned to PFGE clonal groups according to the criteria by which one to three different bands constituted clonally related strains and more than three different bands suggested a different clonal group.23 Statistical analysis Chi-square or Fisher’s exact tests were used to compare proportions and Student’s t-test to compare means. A cumulative Kaplan-Meyer plot was
290
J. Ayats et al.
constructed with the day of ICU admission as the starting point and the first body-site swab positive for multiresistant A. baumannii as the end point. A P-value less than 0.05 was considered statistically significant and all reported P-values were two-sided. The statistical analysis was performed using SPSS/PC and BMDP statistical packages. Results
Twenty-two patients of a total of 95 admitted to the ICU during the study period were excluded (one was admitted for <48h; 20 had only one series of axillary, pharyngeal, and rectal swabs performed, and one had evidence of multiresistant A. baumannii colonization acquired in another hospital ward previous to ICU admission). During the study period, 966 body site swabs from 73 patients were taken and 250 yielded multiresistant A. baumannii. Two different antibiotype patterns were found, the first (RPl) was characterized by resistance to piperacillin, ceftazidime, gentamicin, amikacin, tobramycin, ciprofloxacin, co-trimoxazole and tetracycline (N=34 isolates), and the second pattern RP2 (N= 220) sh owed susceptibility to ciprofloxacin and amikacin with resistance to the other antibiotics. Axillary and pharyngeal colonization by RPl and RP2 strains was observed twice in two patients. Two different clones, A and B were identified by PFGE analysis of chromosomal DNA from the 43 isolates studied. All strains of RPl (N= 11) studied by PFGE belonged to clone A whereas the remaining 32 of RP2 were of clone B (Figure 1). Identity between colonizing and invasive strains was demonstrated by PFGE in all cases studied (eight patients). Body-site colonization due to multiresistant A. baumannii In 48 of the 73 patients (66%), axillary, pharyngeal, and/or faecal colonization was detected, 37 (77%) during the first week, 10 (21%) during the second week, and one (2%) d uring the third week of ICU stay. In nine patients, colonization was detected within the first 48 h: three were admitted from outside the hospital and did not have previous hospital admissions, three came from the observation unit and three from other wards (previous hospital stay: 15,23, and 37 days, respectively). The probability of remaining free of colonization during ICU stay is shown in Figure 2. Correlation between body-site colonization and positive clinical isolates Among the 73 patients, 21 (29%) had positive clinical samples due to A. baumannii; in all of them, axillary, pharyngeal, or faecal colonization was also documented. Body site swabs detected colonization by A. baumannii before clinical samples in 15 of the 21 patients (71%) (mean seven days, range l-20), and was concomitant in two patients. Of the 21 patients with positive clinical samples, 10 were considered to be infected and the remainder as clinical colonization. Twelve sites of infection were
A. baumannii
in
the
ICU
kb
23.1
Figure 1. Pulsed-field gel electrophoresis (PFGE) of A. baumannii genomic DNA after SmaI restriction. Lanes 2-5 (resistance pattern type 2/PFGE B), isolates from axillary, pharyngeal and rectal swabs from a bacteraemic patient, the isolate from blood culture is show in lane 5. Lanes 6-9 (resistance pattern type l/PFGE A), strains recovered from axillary, pharyngeal and rectal swabs, and from the respiratory tract in patient with tracheobronchitis. Lane 1, molecular size marker.
documented: seven respiratory tract (six tracheobronchits and one pneumonia), three bacteraemia, and two surgical site (one peritonitis, and one ventriculitis). Ability to detect colonization All three body site swabs showed the same capacity to detect colonization: 36 of the 48 colonized patients were positive in the axilla and/or pharynx (75%), and 37 (77%) grew the organism from faeces. The rates of colonization using more than one swab sites are shown in Figure 3. In the first series of colonized patients, 20 (42%) had only one positive swab (five axilla, eight pharynx, seven rectum), 17 (35%) had two positive swabs, and 11 (23%) had three positive swabs.
292
J. Ayats et al. 100 90 _ 80 70 60 50 40 30 20 10 ,,\I//
II/IIIIIIII/I
0
7 Days
Figure onization.
2. Kaplan-Meyer
plot
Ax Figure axillary
showing
Ph
3. Positivity rates to detect (Ax), pharyngeal (Ph), and
/IIIII 14 of ICU
proportion
Rc
Ax-Ph
multiresistant rectal (Rc)
stay of
patients
Ax-Re
Ph-Rc
(N=48
with
A. baumannii
col-
Ax-Ph-Rc
A. baumannii swabs
8
21
colonization patients).
by
means
of
Discussion
It is of some concern that there are still no well-defined directives regarding effective infection control measures for large and sustained outbreaks due to multiresistant A. baumannii. 24-30While it has been widely recognized that the hospital environment plays an important role in the epidemiology of these outbreaks, recent reports have also pointed toward patient reservoirs as a major source for A. baumannii infections.7,s”6’25 Since 1992 an increased number of A. baumannii isolates (N= 966 patients) causing infection or colonization has been observed in our hospital,
A. baumannii
in the KU
293
the majority of which (708) belonged to clone A (with resistance pattern 1).19 In September 1994, a new epidemic strain named clone B (N= 67) (susceptible to amikacin and ciprofloxacin) was detected, and it was the most common during the study period (January to May 1995). However, in 1996 clone A was the most prevalent strain, and only 8% of A. baumannii strains belonged to clone B. The surveillance and control measures established since the beginning of the outbreak were successful in the detection of a new outbreak strain which was more susceptible to antibiotics than our endemic strain. In our study, the antibiotype proved to be a useful and rapid method for screening and predicted the emergence of an A. baumannii outbreak. The value of the antibiogram is disputed by other authors,31 but most agree that PFGE analysis gives correlation with antibiotype results, and showed that two different strains were involved in the outbreak, as has been observed in some studies.3,‘“,32,33 The application of barrier methods failed to control the outbreak in our hospital over recent years.*’ Before any additional control measure was introduced, we tried to evaluate the epidemiological role of digestive tract colonization in comparison with other body-site colonizations. In our study, a high proportion of patients admitted to ICU (66%) were found to have axillar, pharyngeal, or rectal colonization due to multiresistant A. baumannii. Colonization was thought to be acquired in ICU since most patients had negative swabs at the time of ICU admission or they came from outside the hospital. The surprising speed with which patients were colonized (77% of patients were colonized during the first week) should be underlined, and was in agreement with our own experience and other previously published studies.7’15 We could not establish an order of body-site colonization because, at the time of diagnosis, more than half of the patients had two or three concomitant positive body-site swabs. However, because of the magnitude of the outbreak, a shorter period than a week between swabs could have helped to clarify the sequence of colonization. Since patients could be colonized before the detection of positive clinical samples, the implementation of barrier precautions in ICU patients, based on the identification of positive clinical samples, may be too late to prevent cross-transmission of strains. Infection control practitioners should evaluate the implementation of epidemiological surveillance programs based on the prospective performance of different body site swabs. The weekly practice of a single body-site swab could miss almost a quarter of the total of colonized patients. From the cost-benefit point of view, one should consider whether this miss rate may be reasonable or, in some special circumstances, whether more sensitive detection by means of a pharyngeal-rectal swab combination was more appropriate. The fact that the skin and the respiratory tract, in addition to the digestive tract, can also be highly colonized with A. baumannii casts doubt on
294
J. Ayats et al.
the contribution of selective intestinal decontamination infection control measure in these kinds of outbreaks.
as an additional
de Investigaciones This study was supported in part by grant no. 9610674 f rom the Fondo Sanitarias de la Seguridad Social (FIS), National Health Service, Spain. Dr X. Corbella was supported by a grant from the “Fundacio August Pi i Sunyer”, Dr M. A. Dominguez by grant no. 94/1112 from the FIS, and Dr C. Ardanuy by grant no. 96/5176 from the FIS.
References 1. Bergogne-Bertzin E, Joly-Guillou ML. Hospital infection with Acinetobacter spp.: an increasing problem. J Hasp Infect 1991; 18 (Suppl. A): 250-25.5. 2. French GL, Casewell MW, Roncoroni AJ, Knight S, Phillips I. A hospital outbreak of antibiotic resistant Acinetobacter anitratus: epidemiology and control. J Hosp Infect 1980; 1: 125-131. 3. Vila J, Amela M, Jimenez de Anta MT. Laboratory investigation of hospital outbreak caused by two different multiresistant Acinetobacter calcoaceticus subsp. anitratus strains. J Clin Microbial 1989; 27: 1086-1089. 4. Sakata H, Fujita K, Maruyama S, Kakehashi H, Mori Y, Yoshioka H. Acinetobacter calcoaceticus biovar. anitratus septicaemia in a neonatal intensive care unit: epidemiology and control. j’ Hasp Infect 1989; 14: 15-22. 5. Constant J, Kemeny E, Oxley C, Perry E, Garber G. Investigation of an outbreak of Acinetobacter calcoaceticus var. anitratus infections in an adult intensive care unit. Am J Infect Control 1990; 18: 288-291. CM, Jarvis WR, Brook JH et al. Epidemic bacteremia due to Acinetobacter 6. Beck-Sague baumannii in five intensive care units. Am J Epidemiol 1990; 132: 723-733. C, Burns J et al. Clinical and molecular epidemiology of Acinetobacter 7. Go ES, Urban infections sensitive only to polymyxin B and sulbactam. Lancet 1994; 344: 1329-l 332. B, Talon D, Vie1 JF et al. Risk factors for nosocomial colonization with 8. Mulin multiresistant Acinetobacter baumannii. EurJ Clin Microbial Infect Dis 199.5; 14: 569-576. 9. Sherertz RJ, Sullivan ML. An outbreak of infection in burn patients: contamination of patients’ mattresses. J Infect Dis 1985; 151: 252-258. J, Gould FK, McPeake P. An outbreak of Acinetobacter respiratory 10. Cefai C, Richards tract infection resulting from incomplete disinfection ventilatory equipment. -7 Hasp Infect 1990; 15: 177-182. 11. Weernink A, Severin WPJ, Tjernberg I, Dijkshoorn L. Pillows, an unexpected source of Acinetobacter. J Hasp Infect 1995; 29: 189-I 99. 12. Taplin D, Rebel1 G, Zaias N. The human skin as source of Mima-HeTelZea infections. J Am Med Assoc 1963; 186: 952. 13. Somerville DA, Noble WC. A note on the Gram-negative bacilli on human skin. Eur J Clin Biol Res 1970; 40: 669. 14. Timsit JF, Garrait V, Misset B, Goldstein FW, Renaud B, Carlet J. The digestive tract is a major site for Acinetobacter baumannii colonization in intensive care unit patients. J Infect Dis 1993; 168: 1336-1337. 15. Corbella X, Pujol M, Ayats J et al. Relevance of digestive tract colonization in the epidemiology of nosocomial infections due to multiresistant Acinetobacter baumannii. Clin Infect Dis 1996; 23: 329-334. 16. Lortholary 0, Fagon JY, Buu-Hoi A et al. Nosocomial adquisition of multiresistant Acinetobacter baumannii: risk factors and prognosis. Clin Infect Dis 1995; 20: 790-796. 17. Joly-Guillou ML, Wolff M, DecrC D, Calvat S, Bergogne-Btrtzin E. Colonization and infection with Acinetobacter baumannii in ICU patients receiving selective digestive decontamination: results of a case-control and molecular epidemiologic investigations (abstract no J-213). Program and abstracts of the 34th Interscience Conference on Antimicrobial Agents and Chemotherapy, Orlando, FLA: American Society for Microbiology, 1994, p. 103. H, Schulze A, Hofmann R, Pulverer G. Skin and mucous membrane colonization 18. Seifert
A.
19.
20. 21.
22.
23.
24. 25.
26.
27.
28.
29. 30. 31.
32.
33.
baumannii
in the
ICU
295
is an important source of nosocomial Acinetobacter buumannii infection: A prospective surveillance study, abstr. 108,009, p. 266. Abstracts of the 7th International Congress fog Infectious Diseases. Hong Kong, 1996. Ayats J, Dominguez MA, Ardanuy C et al. Molecular characterization of multiresistant Acinetobacter baumanki strains isolated in a Spanish hospital. Abstracts of 4th International Symposoum on the Biology of Acinetobacter, Eilat, Israel, 1996. Garner JS, Jarvis WR, Emori TG, Horan TC, Hughes JM. CDC definitions for nosocomial infections. Am J Infect Control 1988; 16: 128-140. National Committee for Clinical Laboratory Standards performance for antimicrobial susceptibility testing. Fifth Informational Supplement. Vilanova, PA: NCCLS, 1994. (NCCLS document no MllO-55). Allardet-Servent A, Bouziges N, Carles-Nurit MJ, Bourg G, Gouby A, Ramuz M. Use of low-frequency-cleavage restriction endonucleases for DNA analysis in epidemiological investigations of nosocomial bacterial infections. r Clin Microbial 1989; 27: 2057-2061. Tenover FC, Arbeit RD, Goering RV, Mickelsen PA, Murray BE, Persing DH, Swaminathan B. Interpreting chromosomal DNA restriction patterns by pulsed-field gel electrophoresisi: criteria for bacteria strain typing. J Clin Microbial 1995; 33: 2233-2239. Bergogne-B&r&in E, Joly-Guillou ML, Vieu JF. Epidemiology of nosocomial infections due to Acinetobacter calcoaceticus. J Hosp Infect 1987; 10: 105-13. Joly-Guillou ML, Brun-Buisson C. Epidemiology of Acinetobacter spp: surveillance and management of outbreaks. In Bergogne-BCrCzin E, Jolly-Guillou ML, Towner KJ, Eds. Acinetobacter: Microbiology, Epidemiology, Infections, Management. Florida: CRC Press Boca Raton; 1996: 71-100. Fang FC, Madinger NE. Resistant nosocomial gram-negative bacillary pathogens: Acinetobacter baumannii, Xanthomonas maltophilia, and Pseudomonas cepacia. Current Clinical Topics in Infectious Diseases 1996; 16: 52-75. Crombach WHJ, Dijkshoorn L, van Noort-Klaassen M, Niessen J, van KnippenbertGordebeke G. Control of an epidemic spread of a multiresistant Acinetobacter calcoaceticus in a hospital. Intensive Care Med 1989; 15: 166-170. Cunha BA, Klimek JJ, Gracewski J, McLaughlin JC, Quintiliani R. A common source outbreak of Acinetobacter pulmonai-y infections traced to Wright respirometers. PostgPud MedJ 1980; 56: 169-172. ,411en KD, Green HT. Hospital outbreak of multi-resistant Acinetobacter anitratus: an airbone mode of spread? J Hosp Infect 1987; 9: 110-119. Bergogne-Bertzin E, Towner KJ. Acinetobucter sp$. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin Microbial Rev 1996; 9: 148-165. Tankovik J, Legrand P, de Gatines G, Chemineau V, Brun-Buisson C, Duval J. Characterization of a hospital outbreak of imipenem-resistant Acinetobacter baumannii by phenotypic and genotypic typing methods. J Clin Microbial 1994; 32: 2677-2681. Gouby A, Carles-Nurit MJ, Bouziges N, Bourg G, Mesnard R, Bouvet PJM. Use of pulsed-field gel electrophoresis for investigation of hospital outbreaks of Acinetobacter buumannii. J Clin Microbiol 1992; 30: 1588-1591. Seifert H, Schulze A, Baginsky R, Pulverer G. Comparison of four different methods for epidemiologic typing of Acinetobacter baumannii. J Clin Micvobiol 1994; 32: 1816-l 819.
of Hospital
Infection
(1997)
37, 287-295
Epidemiological significance of cutaneous, pharyngeal, and digestive tract colonization by multiresistant Acine tobacter baumannii in ICU patients J. Ayats,
X. Corbella *, C. Ardanuy, J. Ariza *, R. Martin
M. A. Dominguez, and J. Liiiares
A. Ricart-f-,
Departments of Microbiology, *Infectious Disease, and j-Intensive Medicine, Hospital de Bellvitge, University of Barcelona, Barcelona, Spain Received
5 March
1997;
Yevised manuscript
accepted
25 j%ne 1997
Summary:
The aim of this prospective study was to assess the relative epidemiological role of digestive tract colonization by Acinetobacter bauman&i, in comparison with other body site colonizations, in patients admitted to intensive care units (ICUs). From January to May 1995, axillary, pharyngeal and rectal swabs were taken together within the first 48 h of admission, and then weekly during ICU stay. Seventy-three patients were included, 48 of them (66%) had axillary, pharyngeal, or rectal colonization with A. baumannii, nine (19%) of these 48 during the first 48 h and the remaining 28 (77%) during the first week. Twenty-one (29%) had clinical samples positive for A. baumannii and axillary, pharyngeal, or rectal colonization. In 15 of these 21 (71%), colonization on body sites occurred prior to isolation from clinical samples (mean seven days, range l-20). Throughout admission, rates of detection of A. baumannii were 75% (36/48) for axillary or pharyngeal swabs and 77% (37/48) for rectal swabs. Combination of two bodv site swabs yielded culture‘ positive rates of 90% (43/48) for axillary-pharyngeal or axillary-rectal sites, and 96% (46/48) for pharyngeal-rectal. Two epidemic clones were defined by antibiotype and pulsed-field gel electrophoresis (PFGE) of SmaI DNA digests in 43 isolates from 11 patients. We conclude that body sites of patients were a major reservoir for A. baumannii infections in the outbreak. This finding casts doubt on the value of selective decontamination of the digestive tract as an additional infection control measure in this kind of outbreak. The weekly performance of pharyngeal and rectal swabs appears to detect A. baumannii colonization early among ICU patients and enables barrier methods to be applied rapidly. Keywords:
A.
baumannii;
epidemiology;
colonization.
Introduction
Acinetobacter baumannii has increasingly hospital outbreaks worldwide.‘-* Although
been involved as an agent of different objects in the hospital
Correspondence to: Dr. Josefina Ayats, Microbiology Department, L’Hospitalet de Llobregat, Barcelona, Spain. Fax: (34)-(3)-263.01.62. This paper was presented in part at the 36th International Conference Chemotherapy, held in iVew Orleans, Louisiana, in September 1996. 0195%6701/97/120287+09
$12.00/O
Hospital
de Bellvitge,
on Antimicrobial
0 1997 The Hospital
287
Agents
Infection
08907 and
Society
288
J. Ayats et al.
environment have been implicated as sources of infections, the major epidemiological features in large and sustained outbreaks remain, as yet, unexplained and the natural reservoir of this species ill-defined.‘-” Since the genus Acinetobacter is a normal inhabitant of human skin,12,13 several authors have postulated that patients could be a major epidemiological reservoir of A. baumannii in hospital outbreaks of infections.7Xs In agreement with others,4”4 we found a high prevalence of digestive tract colonization in our intensive care unit (ICU) population in a previous study.15 As a result, selective intestinal decontamination was proposed as an additional control measure by some.14 However, its contribution to the definitive control of this kind of outbreak is questioned by the observation that the skin and pharynx of patients could also be colonized by A. baumannii.‘“‘8 In order to provide an appropriate basis for the rational management of hospital outbreaks, we performed a prospective study to evaluate the relative epidemiological significance of digestive tract colonization in comparison with two other body sites.
Materials
and methods
Setting Hospital de Bellvitge is a lOOO-bed teaching hospital for adults in Barcelona, Spain, which provides acute medical and surgical care, excluding paediatrics, obstetrics and burns. About 23 000 patients are admitted per year, and it has three 12-bed ICUs with an active organ transplantation program. Since 1992, a significant increase in multiresistant A. baumannii isolates, susceptible only to imipenem and sulbactam, has been observed, and a specific infection control program has been introduced. From September 1994 to May 1995, the concomitant epidemic emergence was noted of a new strain of multiresistant A. baumannii with the same antibiotype, but sensitive to amikacin and ciprofloxacin.15”9 Study design The study was centred in one of the three ICUs (ICU-a), and its objectives were as follows, (1) to evaluate the relative epidemiological role of colonization of each of three body sites (axillary, pharyngeal, and digestive) by multiresistant A. baumannii; (2) to analyse the relationship between different body site colonization and clinical colonizations or infections; and (3) to assess the effectiveness of prospective surveillance of patient colonization by means of body site swabs. Axillary, pharyngeal, and rectal swabs were obtained within the first 48h after admission to ICU, and then weekly during their stay from all patients admitted from January 1 to May 31, 1995. All those patients admitted to the ICU for more than 48h, and who, in addition, had at least two series
A. baumannii
in the ICU
289
of axillary-pharyngeal-rectal swabs performed were included in the study and entered into a computer-assisted protocol. For those free of colonization with A. baumannii, a single additional series of three body site swabs performed seven days after discharge from ICU was required. Some critically ill patients coming from other hospital wards or from outside the hospital are temporally admitted for a few hours or days to a lo-bed observation unit, while waiting for ICU admission. This unit is sited in the emergency department and offers mechanical ventilation. In order to ensure that patients admitted to ICU were not previously colonized with A. baumannii, the same three body site swabs were also taken from all patients admitted to this observation unit during the study period. Clinical colonization and infection dejkitions Standard Center for Disease Control definitions were used.” Specimens obtained from axillary, pharyngeal, and rectal swabs were not considered as clinical samples. Microbiological methods Since all multiresistant A. baumannii strains isolated from clinical specimens during the outbreak were found to be gentamicin-resistant, this antibiotic was used as a selective agent for the screening of samples. Swabs were plated on MacConkey agar, supplemented with 6 pg/mL gentamicin, and on 5% sheep blood agar plates. The plates were incubated aerobically at 37°C for 48h. Isolates were identified as A. baumannii using standard biochemical reactions in a MicroScanTM system (Baxter Diagnostics Inc., West Sacramento, USA), and by their ability to grow at 44°C. Antibiotic susceptibility was performed by a microdilution method in the same system (Baxter). The strains were classified for resistance according to NCCLS criteria.21 Pulsed-field gel electrophoresis (PFGE) was performed for 43 multiresistant A. baumannii strains isolated during the study period in clinical (N=8) and colonized (N=35) samples from 11 patients. Genomic DNA was prepared in agarose plugs as previously described.22 DNA inserts were digested with the endonuclease SmaI according to the manufacturer’s specifications (New England BioLabs, Beverly, MA, USA). DNA restriction fragments were separated by PFGE, using a CHEF-DR III apparatus (Bio-Rad, Hercules, CA, USA). The conditions for electrophoresis were 200 V for 20h, with pulse times ranging from 0.5-l 5 s. Isolates were assigned to PFGE clonal groups according to the criteria by which one to three different bands constituted clonally related strains and more than three different bands suggested a different clonal group.23 Statistical analysis Chi-square or Fisher’s exact tests were used to compare proportions and Student’s t-test to compare means. A cumulative Kaplan-Meyer plot was
290
J. Ayats et al.
constructed with the day of ICU admission as the starting point and the first body-site swab positive for multiresistant A. baumannii as the end point. A P-value less than 0.05 was considered statistically significant and all reported P-values were two-sided. The statistical analysis was performed using SPSS/PC and BMDP statistical packages. Results
Twenty-two patients of a total of 95 admitted to the ICU during the study period were excluded (one was admitted for <48h; 20 had only one series of axillary, pharyngeal, and rectal swabs performed, and one had evidence of multiresistant A. baumannii colonization acquired in another hospital ward previous to ICU admission). During the study period, 966 body site swabs from 73 patients were taken and 250 yielded multiresistant A. baumannii. Two different antibiotype patterns were found, the first (RPl) was characterized by resistance to piperacillin, ceftazidime, gentamicin, amikacin, tobramycin, ciprofloxacin, co-trimoxazole and tetracycline (N=34 isolates), and the second pattern RP2 (N= 220) sh owed susceptibility to ciprofloxacin and amikacin with resistance to the other antibiotics. Axillary and pharyngeal colonization by RPl and RP2 strains was observed twice in two patients. Two different clones, A and B were identified by PFGE analysis of chromosomal DNA from the 43 isolates studied. All strains of RPl (N= 11) studied by PFGE belonged to clone A whereas the remaining 32 of RP2 were of clone B (Figure 1). Identity between colonizing and invasive strains was demonstrated by PFGE in all cases studied (eight patients). Body-site colonization due to multiresistant A. baumannii In 48 of the 73 patients (66%), axillary, pharyngeal, and/or faecal colonization was detected, 37 (77%) during the first week, 10 (21%) during the second week, and one (2%) d uring the third week of ICU stay. In nine patients, colonization was detected within the first 48 h: three were admitted from outside the hospital and did not have previous hospital admissions, three came from the observation unit and three from other wards (previous hospital stay: 15,23, and 37 days, respectively). The probability of remaining free of colonization during ICU stay is shown in Figure 2. Correlation between body-site colonization and positive clinical isolates Among the 73 patients, 21 (29%) had positive clinical samples due to A. baumannii; in all of them, axillary, pharyngeal, or faecal colonization was also documented. Body site swabs detected colonization by A. baumannii before clinical samples in 15 of the 21 patients (71%) (mean seven days, range l-20), and was concomitant in two patients. Of the 21 patients with positive clinical samples, 10 were considered to be infected and the remainder as clinical colonization. Twelve sites of infection were
A. baumannii
in
the
ICU
kb
23.1
Figure 1. Pulsed-field gel electrophoresis (PFGE) of A. baumannii genomic DNA after SmaI restriction. Lanes 2-5 (resistance pattern type 2/PFGE B), isolates from axillary, pharyngeal and rectal swabs from a bacteraemic patient, the isolate from blood culture is show in lane 5. Lanes 6-9 (resistance pattern type l/PFGE A), strains recovered from axillary, pharyngeal and rectal swabs, and from the respiratory tract in patient with tracheobronchitis. Lane 1, molecular size marker.
documented: seven respiratory tract (six tracheobronchits and one pneumonia), three bacteraemia, and two surgical site (one peritonitis, and one ventriculitis). Ability to detect colonization All three body site swabs showed the same capacity to detect colonization: 36 of the 48 colonized patients were positive in the axilla and/or pharynx (75%), and 37 (77%) grew the organism from faeces. The rates of colonization using more than one swab sites are shown in Figure 3. In the first series of colonized patients, 20 (42%) had only one positive swab (five axilla, eight pharynx, seven rectum), 17 (35%) had two positive swabs, and 11 (23%) had three positive swabs.
292
J. Ayats et al. 100 90 _ 80 70 60 50 40 30 20 10 ,,\I//
II/IIIIIIII/I
0
7 Days
Figure onization.
2. Kaplan-Meyer
plot
Ax Figure axillary
showing
Ph
3. Positivity rates to detect (Ax), pharyngeal (Ph), and
/IIIII 14 of ICU
proportion
Rc
Ax-Ph
multiresistant rectal (Rc)
stay of
patients
Ax-Re
Ph-Rc
(N=48
with
A. baumannii
col-
Ax-Ph-Rc
A. baumannii swabs
8
21
colonization patients).
by
means
of
Discussion
It is of some concern that there are still no well-defined directives regarding effective infection control measures for large and sustained outbreaks due to multiresistant A. baumannii. 24-30While it has been widely recognized that the hospital environment plays an important role in the epidemiology of these outbreaks, recent reports have also pointed toward patient reservoirs as a major source for A. baumannii infections.7,s”6’25 Since 1992 an increased number of A. baumannii isolates (N= 966 patients) causing infection or colonization has been observed in our hospital,
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in the KU
293
the majority of which (708) belonged to clone A (with resistance pattern 1).19 In September 1994, a new epidemic strain named clone B (N= 67) (susceptible to amikacin and ciprofloxacin) was detected, and it was the most common during the study period (January to May 1995). However, in 1996 clone A was the most prevalent strain, and only 8% of A. baumannii strains belonged to clone B. The surveillance and control measures established since the beginning of the outbreak were successful in the detection of a new outbreak strain which was more susceptible to antibiotics than our endemic strain. In our study, the antibiotype proved to be a useful and rapid method for screening and predicted the emergence of an A. baumannii outbreak. The value of the antibiogram is disputed by other authors,31 but most agree that PFGE analysis gives correlation with antibiotype results, and showed that two different strains were involved in the outbreak, as has been observed in some studies.3,‘“,32,33 The application of barrier methods failed to control the outbreak in our hospital over recent years.*’ Before any additional control measure was introduced, we tried to evaluate the epidemiological role of digestive tract colonization in comparison with other body-site colonizations. In our study, a high proportion of patients admitted to ICU (66%) were found to have axillar, pharyngeal, or rectal colonization due to multiresistant A. baumannii. Colonization was thought to be acquired in ICU since most patients had negative swabs at the time of ICU admission or they came from outside the hospital. The surprising speed with which patients were colonized (77% of patients were colonized during the first week) should be underlined, and was in agreement with our own experience and other previously published studies.7’15 We could not establish an order of body-site colonization because, at the time of diagnosis, more than half of the patients had two or three concomitant positive body-site swabs. However, because of the magnitude of the outbreak, a shorter period than a week between swabs could have helped to clarify the sequence of colonization. Since patients could be colonized before the detection of positive clinical samples, the implementation of barrier precautions in ICU patients, based on the identification of positive clinical samples, may be too late to prevent cross-transmission of strains. Infection control practitioners should evaluate the implementation of epidemiological surveillance programs based on the prospective performance of different body site swabs. The weekly practice of a single body-site swab could miss almost a quarter of the total of colonized patients. From the cost-benefit point of view, one should consider whether this miss rate may be reasonable or, in some special circumstances, whether more sensitive detection by means of a pharyngeal-rectal swab combination was more appropriate. The fact that the skin and the respiratory tract, in addition to the digestive tract, can also be highly colonized with A. baumannii casts doubt on
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the contribution of selective intestinal decontamination infection control measure in these kinds of outbreaks.
as an additional
de Investigaciones This study was supported in part by grant no. 9610674 f rom the Fondo Sanitarias de la Seguridad Social (FIS), National Health Service, Spain. Dr X. Corbella was supported by a grant from the “Fundacio August Pi i Sunyer”, Dr M. A. Dominguez by grant no. 94/1112 from the FIS, and Dr C. Ardanuy by grant no. 96/5176 from the FIS.
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