Impact of infection control interventions and antibiotic use on hospital MRSA: a multivariate interrupted time-series analysis

https://doi.org/10.1016/j.ijantimicag.2007.04.005Get rights and content

Abstract

Hospitals in the northeast of Scotland have experienced methicillin-resistant Staphylococcus aureus (MRSA) outbreaks since 1997. Several infection control measures were introduced sequentially to control MRSA, and antibiotic use has been monitored. From January 1997 to December 2004, data on the monthly percentage of non-duplicate MRSA infections (%MRSA) were collated from an intervention hospital (IH) and a control hospital (CH). Both hospitals introduced the use of alcohol hand gel in November 2002. Furthermore, the IH introduced an environmental MRSA swabbing programme in March 2001, chlorine disinfection of the environment in September 2001, discharge screening in December 2001, admission screening in November 2003 and environmental audits in March 2004. Multivariate dynamic regression analysis was used to evaluate the longitudinal effects of these interventions as measured by new clinical cases of MRSA. At the IH, the %MRSA increased between January 1998 and January 2001 and then decreased. At the CH, the %MRSA increased from January 1997 to December 2004. Introduction of alcohol hand gel was associated with an absolute decrease in %MRSA of 21% and 30%, respectively, for the IH and CH. At the IH, introduction of chlorine disinfection and environmental swabbing were, respectively, associated with a decrease in %MRSA of 27% immediately and 32% 3 months later. Discharge screening and environmental audit did not significantly affect %MRSA, whereas admission screening was associated with a 22% decrease in %MRSA 4 months later. Increasing macrolide use was associated with increasing %MRSA in both hospitals, and increasing quinolone use was associated with increasing %MRSA in the CH. Implementation of stepwise infection control measures was associated with a decrease in %MRSA in the IH. Introduction of an alcohol gel for hand hygiene was associated with a decrease in %MRSA in both hospitals. Antibiotic use also affects %MRSA, in particular that of macrolides and quinolones.

Introduction

The UK has had one of the highest methicillin-resistant Staphylococcus aureus (MRSA) rates of any European country for the past few years [1], with rates approaching those in the USA [2]. The epidemic spread to the Grampian region of Scotland in 1996 [3]. So far, community-acquired MRSA remains sporadic and the great majority of MRSA is hospital acquired [2]. It is believed that this MRSA epidemic has its origins in many different problems with National Health Service (NHS) hospitals and consequently the solutions are likely to be multifactorial [4], [5].

Fighting epidemic MRSA involves re-enforcement of infection control measures as well as rational use of antimicrobials. However, robust evidence of which control measures are most effective remains largely elusive [2], [4], [5]. Hand hygiene is widely believed to be crucial, but its effective long-term implementation has proved problematic [2]. Variations on the search-and-destroy policy favoured by the Dutch and Scandinavians are widely practiced [6], particularly for contacts of known cases, but admission screening [7] is not yet routinely performed on a hospital-wide basis. In the UK, isolation is often problematic owing to shortage of single rooms in most NHS hospitals, and there is no consensus about the role of environmental MRSA contamination and the need for disinfection of the close patient environment rather than simple cleaning with detergents [8].

This paper uses interrupted time-series analysis to evaluate the longitudinal effects of infection control interventions and antibiotic use on MRSA rates in two Grampian hospitals: one where several interventions were implemented to control MRSA such as environmental disinfection and admission screening; and the other where only standard precautions were used with the exception of contact tracing for clinical MRSA cases. Both hospitals introduced the same alcohol hand gel during the study period.

Section snippets

Settings

The intervention hospital (IH) is a 200-bed district general hospital with most specialties, located 75 miles from Aberdeen in the northeast of Scotland. The control hospital (CH) is a 300-bed hospital for medicine for the elderly and elective orthopaedic surgery situated in Aberdeen.

Microbiology data

Monthly data for all S. aureus collected from clinical diagnostic specimens were exported from the clinical microbiology information system into a Microsoft Access database (Microsoft, Redmond, WA). Only the first

Results

A comparison of the demographics of the two hospitals is shown in Table 1. From January 1997 to December 2004, 1271 non-duplicate clinical S. aureus were isolated from patients at the IH and the observed median monthly percentage of MRSA (%MRSA) was 14.2% (range 0.0–71.4%). At the CH during the same study period, the observed median monthly %MRSA was 30.2% (range 0.0–66.6%) among 2484 non-duplicate clinical S. aureus isolates.

Among 345 and 585 MRSA clinical and screening isolates from the IH

Discussion

This study confirms our previous work on the importance of antibiotic prescribing in the evolution of hospital MRSA [3]. However, even if changes in the consumption of certain antibiotics are an independent factor for changes in %MRSA (Table 3, Table 4), it has traditionally proved difficult to reduce antibiotic consumption.

Our report also confirms previous work of the immediate benefits of alcohol hand gel to improve hand hygiene and to reduce MRSA [2], [5]. However, this was not enough to

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