Tackling contamination of the hospital environment by methicillin-resistant Staphylococcus aureus (MRSA): a comparison between conventional terminal cleaning and hydrogen peroxide vapour decontamination

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Abstract

The hospital environment can sometimes harbour methicillin-resistant Staphylococcus aureus (MRSA) but is not generally regarded as a major source of MRSA infection. We conducted a prospective study in surgical wards of a London teaching hospital affected by MRSA, and compared the effectiveness of standard cleaning with a new method of hydrogen peroxide vapour decontamination. MRSA contamination, measured by surface swabbing was compared before and after terminal cleaning that complied with UK national standards, or hydrogen peroxide vapour decontamination. All isolation rooms, ward bays and bathrooms tested were contaminated with MRSA and several antibiogram types were identified. MRSA was common in sites that might transfer organisms to the hands of staff and was isolated from areas and bed frames used by non-MRSA patients. Seventy-four percent of 359 swabs taken before cleaning yielded MRSA, 70% by direct plating. After cleaning, all areas remained contaminated, with 66% of 124 swabs yielding MRSA, 74% by direct plating. In contrast, after exposing six rooms to hydrogen peroxide vapour, only one of 85 (1.2%) swabs yielded MRSA, by enrichment culture only. The hospital environment can become extensively contaminated with MRSA that is not eliminated by standard cleaning methods. In contrast, hydrogen peroxide vapour decontamination is a highly effective method of eradicating MRSA from rooms, furniture and equipment. Further work is needed to determine the importance of environmental contamination with MRSA and the effect on hospital infection rates of effective decontamination.

Introduction

Infection with methicillin-resistant Staphylococcus aureus (MRSA) has become endemic in hospitals around the world despite concerted efforts by infection control professionals.1 In the UK, the proportion of blood isolates of S. aureus that are resistant to methicillin has risen from just a few percent in the late 1980s to over 30%, with rates of over 40% seen in tertiary referral hospitals.2., 3., 4. Similar prevalence rates are reported from other European countries4 and the US.5 S. aureus is the commonest cause of surgical-site infection in English hospitals, and more than half the infecting strains are methicillin resistant.6 Nearly all MRSA infections are acquired in hospital and many of them are potentially preventable.7

MRSA is transmitted between patients on the hands of hospital staff, and handwashing is widely recognized as the single most important factor for prevention of colonization and infection.8., 9. Nevertheless, despite the implementation of standard infection control practices, the widespread failure to control MRSA is striking.10 The hospital environment may be another important, but neglected, factor in hospital cross-infection.11., 12., 13.

Since the 1950s, hospital design and hygienic practices have been largely directed at controlling S. aureus contamination of air, hands, instruments and surfaces. By the late 1970s these practices had been so successful that the hospital environment was considered to make little contribution to the spread of hospital infection.14., 15. Nevertheless, S. aureus and MRSA can survive on dry surfaces for prolonged periods,12., 16., 17., 18., 19., 20. and many investigations since the 1980s have shown that these organisms can contaminate surfaces and equipment touched by hospital staff.12., 21., 22., 23., 24., 25., 26. Standards of hospital cleaning have declined11., 13., 27. and floors, furniture and medical equipment may now be sources of MRSA transmission.11., 12., 13., 22.

The current guidelines for the control of MRSA in UK hospitals recognize the potential importance of the environment and recommend terminal cleaning of isolation rooms after patient discharge.2 In practice, manual cleaning of complex environments containing beds, furniture, medical equipment and soft furnishings is difficult. This problem may be solved by gaseous decontamination methods.

Hydrogen peroxide vapour is effective against a wide range of organisms, including bacterial endospores,28 vegetative bacteria29 and viruses.30 It is safer than other disinfectant gases such as formaldehyde and ethylene oxide, and decomposes to water and oxygen. It has been used to decontaminate laboratory and medical equipment, pharmaceutical manufacturing facilities and animal houses31., 32., 33., 34., 35. but has not previously been applied in healthcare settings. The present study investigated MRSA environmental contamination in a hospital where MRSA infection is common, and compared the effectiveness of standard hospital environmental cleaning with a commercial hydrogen peroxide vapour decontamination system.

Section snippets

Setting

This investigation was conducted in a 1200-bed London teaching hospital where MRSA colonization and infection is common. Environmental sampling was conducted on four different wards dealing with vascular, lower gastrointestinal, orthopaedic/plastic and general surgical patients. Environmental decontamination with hydrogen peroxide vapour was conducted on the vascular surgery ward only.

Surface samples were taken from the following locations: ward single side rooms that had recently been used to

MRSA environmental contamination in ward side rooms, bays and bathrooms before terminal cleaning

Three hundred and fifty-nine swabs were taken before cleaning from 18 ward side rooms, two four-bedded ward bays and four bathrooms recently occupied or used by patients infected or colonized with MRSA (15 of the 18 patients in the side rooms were infected with MRSA and three were colonized). MRSA was recovered from every side room, bay and bathroom. Seventy-four percent of swabs yielded MRSA; 70% of positive cultures were by direct plating and 30% by broth enrichment (Table I).

Four (50%) of

Discussion

We found extensive surface environmental contamination with MRSA in ward areas previously occupied by colonized or infected patients. The level of contamination was much higher than that reported by Boyce et al. (1997)22 who used similar culture methods and found 27% of 350 environmental surfaces around MRSA patients to be contaminated compared with 74% of 359 in our study. Boyce et al. (1997)22 identified MRSA in 73% of 22 rooms of infected patients and 69% of 16 rooms of colonized patients,

Acknowledgements

We acknowledge the helpful cooperation of the staff and patients on the wards involved in this study. The study was supported financially by BIOQUELL PLC, who were involved in the conception, design and execution of the research project. All aspects of the study were conducted collaboratively.

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