Identification and control of an outbreak of ciprofloxacin-susceptible EMRSA-15 on a neonatal unit

Journal of Hospital Infection (2007) 67, 232e239

www.elsevierhealth.com/journals/jhin

Identification and control of an outbreak of ciprofloxacin-susceptible EMRSA-15 on a neonatal unit* J.A. Otter a, J.L. Klein b, T.L. Watts c, A.M. Kearns d, G.L. French a,* a

Infection and Immunology Delivery Unit, St Thomas’ Hospital and King’s College London, UK Infection and Immunology Delivery Unit, St Thomas’ Hospital, London, UK c Children’s Services, St Thomas’ Hospital, London, UK d Staphylococcus Reference Laboratory, Centre for Infections, HPA, London, UK b

Received 17 May 2007; accepted 27 July 2007 Available online 22 October 2007

KEYWORDS MRSA; Outbreak; Neonatal; Environmental contamination

Summary We report the identification and control of an outbreak of a ciprofloxacin-susceptible strain of UK epidemic meticillin-resistant Staphylococcus aureus (EMRSA)-15 on a neonatal unit (NNU). All babies were screened for MRSA on admission using ciprofloxacin-containing media which did not detect the outbreak strain. The first identified case was a premature baby who developed MRSA bacteraemia with associated tibial osteomyelitis and multiple subcutaneous abscesses. The outbreak strain was subsequently identified in the nasopharyngeal secretions of a second child who was not clinically infected. Screening of all patients on the NNU using non-ciprofloxacin-media identified two other colonised babies. All four patient isolates were EMRSA-15, spa type t022, SCCmec IV, PantoneValentine leucocidin (PVL) negative, indistinguishable by pulsedfield gel electrophoresis and susceptible to all non-b-lactam antimicrobials tested. The outbreak strain was cultured from four of 48 environmental sites in a communal milk-expressing room. Unsupervised movement of mothers to and from the milk-expressing room may have contributed to the outbreak. Control measures included cohort isolation of affected babies, improved environmental cleaning, increased emphasis on hand hygiene and education of mothers. Ciprofloxacin-containing media should

* This work was presented in part at the 17th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), 31 March to 3 April 2007. * Corresponding author. Address: Department of Infection, 5th Floor, North Wing, St Thomas’ Hospital, Lambeth Palace Road, London SE1 7EH, UK. Tel.: þ44 207 188 3127; fax: þ44 207 928 0730. E-mail address: [email protected]

0195-6701/$ - see front matter ª 2007 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jhin.2007.07.024

Control of an MRSA outbreak on neonatal unit

233

be used with caution for MRSA screening in settings where ciprofloxacinsusceptible strains (including community-associated MRSA) are increasing in prevalence. ª 2007 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved.

Introduction Meticillin-resistant Staphylococcus aureus (MRSA) infections in both adults and children in the UK are usually caused by epidemic (E-MRSA-15 and -16) and multidrug-resistant healthcareassociated (HA-MRSA) strains.1 Outbreaks on neonatal units (NNUs) are uncommon but have been reported intermittently since the 1970s and have usually been caused by HA-MRSA.2e4 Recently, there have been reports of paediatric and NNU outbreaks caused by multidrug-susceptible community-associated strains of MRSA (CA-MRSA).5 These have occurred mainly in the USA, but outbreaks have occurred elsewhere, including the UK.6 CA-MRSA typically affects young, previously healthy individuals without prior healthcare contact, and can be distinguished from HA-MRSA by their susceptibility to most non-b-lactam antimicrobials, distinct genetic backgrounds [usually carrying type IV or V staphylococcal cassette chromosome mec (SCCmec)] and frequent carriage of PantoneValentine leucocidin (PVL).7 We describe an outbreak and subsequent control on a NNU of an unusually antimicrobialsusceptible strain of MRSA that was initially thought to be a CA-MRSA strain but was found to be a subtype of EMRSA-15. Environmental contamination may have contributed to the spread of this organism.

Methods Setting Guy’s and St Thomas’ NHS Foundation Hospital Trust is a 1200-bed teaching and tertiary referral hospital located on two sites in London. The NNU is a 36-bed unit on the St Thomas’ site comprising a 12-bed neonatal intensive care unit (NICU) divided into three rooms and a 24-bed special care baby unit (SCBU) divided into four rooms. The NICU and SCBU are separated by a swing door; they have individual reception areas but share facilities such as a communal milk-expressing room (where

mothers use several communal breast pumps to provide breast milk for their babies), a staff room and a hand-washing area for staff and visitors. Healthcare workers (HCWs) are cohorted on their shifts to either NICU or SCBU. The wards are cleaned daily by damp dusting all fixtures and fittings and damp mopping the floor with a detergent solution. Terminal cleaning after patient discharge follows a similar regimen but includes the use of sodium hypochlorite-containing agents.

MRSA surveillance, screening and culture When MRSA is isolated on the NNU, a surveillance system provides an immediate alert to the infection control team which then liaises with the appropriate clinicians and nurses. In addition, babies are screened for MRSA carriage on admission by nose, throat, axilla, groin and rectal swabs cultured in screening broth containing 20 mg/L ciprofloxacin as a selective agent.8 Clinical samples from infected sites are cultured on non-ciprofloxacin-containing media.

Identification and characterisation of MRSA The first isolate identified in this outbreak was a ciprofloxacin-susceptible organism isolated from a clinical specimen; subsequent screening swabs were therefore cultured on a chromogenic MRSA medium (Oxoid, Basingstoke, UK) that uses cefoxitin rather than ciprofloxacin as a selective agent. Presumptive MRSA were confirmed as S. aureus by Gram’s stain, production of coagulase (Pastorex Staph Plus, Bio-Rad, Hemel Hempstead, UK) and mannitol fermentation. Susceptibility to the following antimicrobial agents was tested by disc diffusion: meticillin, penicillin, gentamicin, neomycin, vancomycin, erythromycin, fusidic acid, tetracycline, linezolid, rifampicin, mupirocin, trimethoprim and ciprofloxacin.9 DNA was extracted from MRSA by use of a commercial kit (ChargeSwitch gDNA mini-bacteria kit, Invitrogen Ltd, Paisley, UK). Polymerase chain reaction was used to confirm the presence of mecA and determine the SCCmec type.10 Spa Typing was performed as described by Harmsen et al. and

234 the HPA Staphylococcus Reference Laboratory characterised isolates by phage typing, pulsedfield gel electrophoresis (PFGE) and toxin gene profiling (including enterotoxins AeD and GeJ; toxic shock syndrome toxin-1; epidermolytic toxins A, B and D and PVL).11,12 The ciprofloxacin minimum inhibitory concentration (MIC) was determined by automated broth microdilution (Vitek 2, bioMe ´rieux, Marcy-l’Etoile, France).

Environmental screening Sterile cotton-tipped swabs were moistened in Brain-Heart Infusion (BHI) broth and used to sample approximately 25 cm2 areas at 48 sites in the NNU. Hand-touch sites were chosen for sampling where possible and included cots or incubators (N ¼ 9), electronic monitors (N ¼ 7), door handles (N ¼ 7), nursing stations (N ¼ 6), computer keyboards (N ¼ 5), suction fittings (N ¼ 4), composite samples from breast pumps and associated chair arms (N ¼ 4) and floors (N ¼ 4). Swabs were plated directly onto BairdeParker (BP) agar, then broken into 10 mL BHI and subcultured onto BP agar after 48 h incubation at 37  C as an enrichment step. No ciprofloxacin was added to the media used for the environmental sampling. BP plates were incubated for 48 h and presumptive S. aureus was confirmed and characterised as described above.

Results Description of the outbreak Baby 1 was admitted to the NNU in June 2006 at 27 weeks of gestation with a birthweight of 900 g following emergency caesarean section for abruption. MRSA was cultured from endotracheal tube secretions on the day of extubation, seven days after birth. This baby subsequently developed MRSA bacteraemia with associated tibial osteomyelitis and multiple subcutaneous abscesses. One month after the first MRSA isolate from baby 1, a similar organism was isolated from a nasopharyngeal aspirate from baby 2, although the baby did not have signs of staphylococcal infection (Figures 1 and 2). Five days later, unit-wide screening identified two further asymptomatic babies (3 and 4) colonised with the outbreak strain (Figures 1 and 2). Baby 1 was treated with a six-week course of vancomycin plus rifampicin and discharged home in good health. The three colonised babies were not treated and decolonisation was not attempted. All four babies were nursed using contact

J.A. Otter et al. precautions until they were discharged home in good health. Baby 3 had been nursed in the same room as baby 1 at the time of baby 1’s initial MRSA-related illness (Figure 2). Babies 2e4 were subsequently nursed in the same room up to the time that they were found to be MRSA positive. All four babies had screened negative for MRSA on admission but the screening medium contained ciprofloxacin as a selective agent, so would not have detected the ciprofloxacin-susceptible outbreak strain. The mothers of the four affected babies were screened for MRSA using pooled swabs from the nose, axilla and groin cultured on non-ciprofloxacincontaining media in July 2006 and none were found to be colonised. However, the mothers of babies 1 and 4 had histories of prior healthcare contact in our hospital; the mother of baby 4 had a 15-day antenatal inpatient stay in April 2006.

Environmental screening The first environmental screen was conducted two days after the identification of MRSA on babies 3 and 4. Ten sites were sampled in NICU 3 where the four MRSA-positive babies had been cohorted for 2 days; 10 in SCBU 2 from where an MRSA-positive baby had been transferred approximately one month prior to sampling; 10 in SCBU 3 after terminal cleaning following the transfer of MRSA-positive babies and 10 on the open unit, focusing on the milk-expressing room (Figure 2). Five days later, eight sites were sampled in NICU 3 immediately after terminal cleaning following the transfer of MRSA-positive babies (Figure 2). S. aureus was cultured from 17 (35.4%) of the 48 environmental sites; eight (16.7%) were MRSA and one of the sites was positive for both MRSA and meticillin-susceptible S. aureus (MSSA) (Table I). The outbreak strain was cultured from a cot and the floor, and two unrelated MRSA strains were cultured from the cohort room of the four affected babies (Figure 1). The outbreak strain was cultured by direct plating from an electronic monitor in the cohort room immediately after deep cleaning following the transfer of the MRSApositive babies (Figure 1). A non-outbreak MRSA strain and MSSA were cultured from a suction fitting in SCBU 3, which had undergone a deep clean immediately prior to sampling following transfer of the MRSA-positive babies (Table I). There was heavy bacterial growth from all five samples taken in the milk-expressing room. The outbreak strain was cultured from the door handle and a different MRSA strain from a combined sample from a breast pump and associated chair

Source

Specimen

Antibiograma

spa

Toxin gene profileb

SCCmecc

NICU 3

Suction fitting

Cip, Gent

t032

seg, sei

Non-typeable

SCBU 3

Cot

Cip, Gent

t032

Not done

Non-typeable

Open unit

Breast pump/chair

Cip, Gent

t032

Not done

Non-typeable

NICU 3

Monitor

Cip, Gent, Ery

t1370

seg, sei

Non-typeable

NICU 3

Floor

None

t022

Not done

IV

NICU 3

Cot

None

t022

Not done

IV

Open unit

Door

None

t022

Not done

IV

Baby 4

Screen

None

t022

Not done

IV

Baby 2

NPA

None

t022

Not done

IV

Baby 3

NPA

None

t022

Not done

IV

Baby 1

ETT secretions

None

t022

sec, seg, sei

IV

NICU 3b

Monitor

None

t022

Not done

IV

Control of an MRSA outbreak on neonatal unit

PFGE dendrogram

similarity 80 90 100

Patient isolates are shown in bold. PFGE, pulsed-field gel electrophoresis; NPA, nasopharyngeal aspirate; ETT, endotracheal tube; NICU 3b, post-cleaning. aAntimicrobial resistance in addition to the β-lactams; Cip, ciprofloxacin; Gent, gentamicin; Ery, erythromycin. bsec, seg, sei, staphylococcal enterotoxins C, G and I. cSCCmec, staphylococcal cassette chromosome mec, non-typeable isolates were positive for mecA and locus D using the assay described by Oliveira and de Lencastre.10 Figure 1

Characteristics of meticillin-resistant Staphylococcus aureus (MRSA) from patients and the environment.

235

236

J.A. Otter et al.

Characteristics of the outbreak strain Baby 1

Baby 2

Baby 3

Baby 4 0

10

20

30

40 50 60 Time (days)

70

80

90 100

Figure 2 Temporal distribution of admissions, discharges, MRSA screens, first identification of MRSA on the four affected babies and timing of environmental sampling. White bar: MRSA status unknown; grey bar: MRSA positive. White arrowhead: admission MRSA screen (cultured on ciprofloxacin-containing media); black arrowhead: MRSA screen or clinically indicated sample cultured on non-ciprofloxacin-containing media; black arrows: environmental screen.

arm. MSSA was cultured from a third site in the milk-expressing room (Table I).

Outbreak interventions A multidisciplinary outbreak group was convened when MRSA was cultured from baby 2; an incident was declared and appropriate Trust management and clinical staff were kept informed of developments. The group recommended screening all patients for MRSA, which identified two further cases. No HCWs were screened. Immediate interventions comprised cohort isolation of all four affected babies in a single room and an emphasis on hand hygiene for both staff and visitors. When environmental contamination was identified on the NNU, the entire unit was deep-cleaned using chlorinecontaining disinfectant. Since the investigations suggested that the milkexpressing room may have contributed to the outbreak, a policy of twice daily detergent cleaning of this area was implemented, the room was renovated and unsuitable furniture was replaced. Posters emphasising the need for hand hygiene during the milk-expressing process were displayed and mothers were educated on hygienic practice. No further cases were identified after the implementation of these measures and the outbreak strain was not identified on the NNU in the subsequent 12 months.

The MRSA outbreak strain was susceptible to all the non-b-lactam antibiotics tested, including ciprofloxacin (MIC 0.5 mg/L). It was spa type 022 (t022) and PVL negative, with a phage pattern, PFGE profile, SCCmec type, and toxin gene profile consistent with EMRSA-15 (Figure 1). All eight environmental isolates were PVL negative EMRSA-15; four were indistinguishable from the outbreak strain and the remainder represented two different ciprofloxacinresistant subtypes of EMRSA-15 by PFGE which belonged to spa types t032 and t1370 (Figure 1).

Discussion MRSA is uncommon on our NNU; it had been isolated from only four epidemiologically unrelated patients in the 12 months prior to this outbreak and all were ciprofloxacin-resistant. However, it is possible that some MRSA was missed due to the routine use of ciprofloxacin-containing screening media. The outbreak strain was initially mistaken for CA-MRSA because of the clinical presentation and multidrug susceptibility. Subsequent molecular typing identified the strain as a subtype of EMRSA-15, which produced serious invasive disease in one neonate. Ciprofloxacin-susceptible MRSA is rare in our hospital and only two (3.2%) of 62 randomly selected EMRSA-15 referrals to the HPA in the UK were ciprofloxacin susceptible.13,14 However, our experience with this outbreak of a ciprofloxacinsusceptible strain of EMRSA-15 and the emergence elsewhere of ciprofloxacin-susceptible CA-MRSA indicates that ciprofloxacin-containing selective media should be used with caution, particularly for MRSA screening in paediatrics.6,15 We were unable to identify the source of the outbreak and do not know whether any of the four affected babies were colonised with MRSA on admission to the NNU because ciprofloxacin was used as a selective agent in the screening media. Although all four mothers were negative for MRSA shortly after the outbreak, two of them had had recent healthcare contact and it is possible that this was the source of the organism.16 Transmission of S. aureus on NNUs has occurred via HCW hands and persistent HCW nasal carriage; environmental contamination has also been implicated.2,3,17e20 One study identified MRSA on 45 (59.2%) of 85 surfaces sampled on an NNU, including patient charts, door handles and medical equipment.19 Five (9.2%) of 54 sites sampled on

Control of an MRSA outbreak on neonatal unit Table I

237

Environmental sampling results (N ¼ no. of sites sampled) according to culture type NICU 3a

SCBU 2/SCBU 3/NICU 3 after dischargeb

(N ¼ 10) Direct plating e

1 (10.0)

MRSA

4 (40.0)

4 (40.0)

MRSApositive sites

2  cot Monitor

e 2 (7.1)

Direct and enrichment

(N ¼ 48)

2 (7.1)

Direct plating

Direct and enrichment

Direct plating Direct and enrichment

3 (30.0)

4 (40.0)

3 (6.3)

10 (20.8)

2 (7.1)

1 (10.0)

2 (20.0)

7 (14.5)

8 (16.7)

2  cot Door handle Breast Door handle 2  monitor pump/ chair arm Floor Suction fitting Breast pump/ chair arm

Monitor Suction fitting

5 (50.0)

(N ¼ 10)

5 (17.9)

Floor

Total 4 (40.0) S. aureus

Total

(N ¼ 28)

Direct and Direct enrichment plating

MSSA

Open unit

6 (21.4)c

4 (40.0)

6 (60.0)

10 (20.8)

17 (35.4)c

Values in parentheses are percentages. NICU, neonatal intensive care unit; SCBU, special care baby unit; MSSA, meticillin-susceptible Staphylococcus aureus; MRSA, meticillin-resistant Staphylococcus aureus. a Four MRSA-positive neonates had been cohorted in NICU 3 for 2 days prior to sampling. b Ten swabs were taken in SCBU 2 from which one MRSA-positive neonate was transferred approximately one month before sampling; 10 swabs were taken in SCBU 3 and eight in NICU 3 immediately after terminal cleaning following the transfer of three MRSA-positive babies. c MRSA and MSSA were cultured from one site.

another NNU were contaminated with an outbreak strain, including a door handle.3 During an extended outbreak of epidermolytic toxinpositive S. aureus on two neonatal units, 11 (7.8%) of 141 environmental surveillance cultures from surfaces and air were contaminated with exfoliative toxin-producing epidemic strains.20 By contrast, epidemic strains were not cultured from more than 600 surveillance cultures of HCW and uninfected babies.20 However, other studies have not identified a significant environmental reservoir for NNU outbreaks despite epidermolytic sampling.2 Due to the small number of babies affected in this outbreak we did not investigate HCW hand contamination or nasal colonisation but we did culture MRSA from eight (16.7%) of 48 environmental sites, including handtouch sites before and after terminal cleaning. Contamination of the hospital environment with MRSA is well recognised and may contribute to MRSA transmission.21e23 MRSA can contaminate the hands of HCWs following contact with environmental surfaces in the absence of patient contact.21,24 The heavy contamination of the milk-expressing room with organisms that included the outbreak strain and other MRSA suggests that this room could have been a focus for transmission, possibly involving the hands of mothers.

In the present outbreak, half of the MRSA environmental isolates were subtypes of EMRSA15 different from the outbreak strain (Figure 1). All four non-outbreak environmental MRSA were non-typeable by the SCCmec method used, although non-typeable SCCmec regions have been reported previously.12 The origin of these non-outbreak strains is unknown; they may have survived from previous incidents or may have been derived from patients, staff or visitors. Lejeune et al. reported a similar experience in their study, in which only 27% of their MRSA environmental isolates were identical to the predominant patient isolate.3 Three different EMRSA-15 genotypes were identified during this outbreak, distinguishable by both PFGE and spa typing (Figure 1). The PFGE profile of the outbreak strain was not representative of one of the banding patterns commonly seen among EMRSA-15 in the UK, whereas t022 is a common spa type in this lineage.25 Other studies have found that PFGE is more discriminatory than spa typing, but that the combined use of PFGE and spa is more discriminatory than either method alone.26,27 In summary, we have reported a small outbreak of ciprofloxacin-susceptible EMRSA-15 on a neonatal unit, in which one child suffered serious infection and three others were colonised. The

238 outbreak strain and other MRSA types were isolated from several environmental samples. The origin of the outbreak was not determined, but the mothers of two of the colonised babies had had prior hospital contact. Environmental contamination and unsupervised movement of mothers to and from a milk expression room may have contributed to transmission. Although all babies admitted to the unit were screened for MRSA carriage, this was done with a ciprofloxacincontaining medium that did not support the growth of the outbreak organism. We therefore recommend that ciprofloxacin-containing screening media should be used with caution in paediatrics, where ciprofloxacin-susceptible MRSA (including community-associated strains) are increasing in prevalence.28,29

Acknowledgements None. Conflict of interest statement J.A.O. is employed part-time by BIOQUELL (UK) Ltd, which was not involved in any aspect of the production of this article. J.L.K, T.L.W., A.M.K. and G.L.F. have no conflicts of interest. Funding sources J.A.O. is supported by a grant from the Royal Commission for the Exhibition of 1851, London, UK.

References 1. Johnson AP, Aucken HM, Cavendish S, et al. Dominance of EMRSA-15 and -16 among MRSA causing nosocomial bacteraemia in the UK: analysis of isolates from the European Antimicrobial Resistance Surveillance System (EARSS). J Antimicrob Chemother 2001;48:143e144. 2. Farrington M, Ling J, Ling T, French GL. Outbreaks of infection with methicillin-resistant Staphylococcus aureus on neonatal and burns units of a new hospital. Epidemiol Infect 1990;105:215e228. 3. Lejeune B, Buzit-Losquin F, Flohic AMS, Le Bras MP, Alix D. Outbreak of gentamicin-methicillin-resistant Staphylococcus aureus infection in an intensive care unit for children. J Hosp Infect 1986;7:21e25. 4. Michel MF, Priem CC. Control at hospital level of infections by methicillin-resistant staphylococci in children. J Hyg (Lond) 1971;69:453e460. 5. Otter JA, French GL. Nosocomial transmission of community-associated methicillin-resistant Staphylococcus aureus: an emerging threat. Lancet Infect Dis 2006;6: 753e755. 6. David MD, Kearns AM, Gossain S, Ganner M, Holmes A. Community-associated meticillin-resistant Staphylococcus aureus: nosocomial transmission in a neonatal unit. J Hosp Infect 2006;64:244e250.

J.A. Otter et al. 7. Zetola N, Francis JS, Nuermberger EL, Bishai WR. Community-acquired meticillin-resistant Staphylococcus aureus: an emerging threat. Lancet Infect Dis 2005;5: 275e286. 8. Gurran C, Holliday MG, Perry JD, Ford M, Morgan S, Orr KE. A novel selective medium for the detection of methicillinresistant Staphylococcus aureus enabling result reporting in under 24 h. J Hosp Infect 2002;52:148e151. 9. Andrews JM. BSAC standardized disc susceptibility testing method. J Antimicrob Chemother 2001;48(Suppl. 1): 43e57. 10. Oliveira DC, de Lencastre H. Multiplex PCR strategy for rapid identification of structural types and variants of the mec element in methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 2002;46:2155e2161. 11. Harmsen D, Claus H, Witte W, et al. Typing of methicillinresistant Staphylococcus aureus in a university hospital setting by using novel software for spa repeat determination and database management. J Clin Microbiol 2003;41: 5442e5448. 12. Holmes A, Ganner M, McGuane S, Pitt TL, Cookson BD, Kearns AM. Staphylococcus aureus isolates carrying PantoneValentine leucocidin genes in England and Wales: frequency, characterization, and association with clinical disease. J Clin Microbiol 2005;43:2384e2390. 13. Otter JA, French GL. P1587 The molecular epidemiology of community-associated methicillin-resistant Staphylococcus aureus in a London teaching hospital. Int J Antimicrob Agents 2007;29(Suppl. 2):S445eS446. 14. Hill RLR, Kearns AM, Pike R, et al. Does ciprofloxacin susceptibility provide a reliable phenotypic marker for community-associated MRSA? 46th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, 27e30 September 2006. 15. Health Protection Agency. Community MRSA in England and Wales: definition through strain characterisation. Comm Dis Rep Weekly 2005;15. 16. Morel AS, Wu F, Della-Latta P, Cronquist A, Rubenstein D, Saiman L. Nosocomial transmission of methicillin-resistant Staphylococcus aureus from a mother to her preterm quadruplet infants. Am J Infect Control 2002;30:170e173. 17. Wolinsky E, Lipsitz PJ, Mortimer Jr EA, Rammelkamp Jr CH. Acquisition of staphylococci by newborns. Direct versus indirect transmission. Lancet 1960;2:620e622. 18. Dancer SJ, Poston SM, East J, Simmons NA, Noble WC. An outbreak of pemphigus neonatorum. J Infect 1990;20: 73e82. 19. Fujimura S, Kato S, Hashimoto M, Takeda H, Maki F, Watanabe A. Survey of methicillin-resistant Staphylococcus aureus from neonates and the environment in the NICU. J Infect Chemother 2004;10:131e132. 20. Kaplan MH, Chmel H, Hsieh HC, Stephens A, Brinsko V. Importance of exfoliatin toxin A production by Staphylococcus aureus strains isolated from clustered epidemics of neonatal pustulosis. J Clin Microbiol 1986;23:83e91. 21. Boyce JM, Potter-Bynoe G, Chenevert C, King T. Environmental contamination due to methicillin-resistant Staphylococcus aureus: possible infection control implications. Infect Control Hosp Epidemiol 1997;18:622e627. 22. French GL, Otter JA, Shannon KP, Adams NM, Watling D, Parks MJ. Tackling contamination of the hospital environment by methicillin-resistant Staphylococcus aureus (MRSA): a comparison between conventional terminal cleaning and hydrogen peroxide vapour decontamination. J Hosp Infect 2004;57:31e37. 23. Hardy KJ, Oppenheim BA, Gossain S, Gao F, Hawkey PM. A study of the relationship between environmental

Control of an MRSA outbreak on neonatal unit contamination with methicillin-resistant Staphylococcus aureus (MRSA) and patients’ acquisition of MRSA. Infect Control Hosp Epidemiol 2006;27:127e132. 24. Bhalla A, Pultz NJ, Gries DM, et al. Acquisition of nosocomial pathogens on hands after contact with environmental surfaces near hospitalized patients. Infect Control Hosp Epidemiol 2004;25:164e167. 25. O’Neill GL, Murchan S, Gil-Setas A, Aucken HM. Identification and characterization of phage variants of a strain of epidemic methicillin-resistant Staphylococcus aureus (EMRSA-15). J Clin Microbiol 2001;39:1540e1548. 26. Strommenger B, Kettlitz C, Weniger T, Harmsen D, Friedrich AW, Witte W. Assignment of Staphylococcus isolates to groups by

239 spa typing, SmaI macrorestriction analysis, and multilocus sequence typing. J Clin Microbiol 2006;44:2533e2540. 27. Moodley A, Stegger M, Bagcigil AF, et al. spa typing of methicillin-resistant Staphylococcus aureus isolated from domestic animals and veterinary staff in the UK and Ireland. J Antimicrob Chemother 2006;58:1118e1123. 28. David MZ, Crawford SE, Boyle-Vavra S, Hostetler MA, Kim DC, Daum RS. Contrasting pediatric and adult methicillin-resistant Staphylococcus aureus isolates. Emerg Infect Dis 2006;12:631e637. 29. Adedeji A, Weller TM, Gray JW. MRSA in children presenting to hospitals in Birmingham, UK. J Hosp Infect 2007; 65:29e34.