Progression from new methicillin-resistant Staphylococcus aureus colonisation to infection: an observational study in a hospital cohort

Michelle Nd Balm,Paul A Tambyah,Andrew A Lover,Dale A Fisher,Sharon Salmon

doi:10.1186/1471-2334-13-491

Abstract

BackgroundPatients newly colonised with methicillin-resistant Staphylococcus aureus (MRSA) are at higher risk of clinical MRSA infection. At present, there are limited data on the duration or magnitude of this risk in a hospital population with a known time of MRSA acquisition.MethodsA retrospective cohort study of 909 adult patients known to have newly identified MRSA colonisation during admission to National University Hospital, Singapore between 1 July 2007 and 30 June 2011 was undertaken. Patients were excluded if they had history of previous MRSA colonisation or infection, or if they had been a hospital inpatient in the preceding 12 months. Data were collected on the development of MRSA infection requiring hospitalisation up to 30 June 2012.ResultsOf 840 patients newly colonised with MRSA as identified on active surveillance and not clinical specimens, 546 were men (65.0%) and the median age was 65 years (range 18–103 years). Median follow up was 24 months (range 0 –64 months, 85.1% followed >6 months). Clinical infection occurred in 121 patients (14.4%) with median time to infection of 22 days (95% CI 14–31). Overall 71.9% (87/121) of infected patients developed infection within 60 days of the date MRSA colonisation was detected. However, 17/121 patients (14.0%) developed clinical infection more than six months after documented MRSA acquisition. The most common sites of clinical infection were skin and soft tissue (49/121, 40.5%, 95% CI 31.7-49.8), respiratory tract (37/121, 30.6%, 95% CI 22.5-39.6) and bone and joint infections (14/121, 11.6%, 95% CI 6.5-18.7). Thirteen patients (13/121, 10.7%, 95% CI 5.8-17.7) had bacteraemias, of which six (5.0% 95% CI 1.8-10.5) were primary and seven (5.7%, 95% CI 2.3-11.6) were secondary to infection at other sites. Crude mortality at 30 days and six months was higher in patients with MRSA infection than colonisation alone (aOR 5.49, 95% CI 2.75-10.95, p<0.001 and aOR 2.94, 95% CI 1.78-4.85, p<0.001 respectively).ConclusionRisk of clinical infection is highest soon after MRSA acquisition. Prevention of MRSA acquisition in hospital will have significant impact on morbidity and mortality for patients.

Highlights

Patients newly colonised with methicillin-resistant Staphylococcus aureus (MRSA) are at higher risk of clinical MRSA infection
Patient records were reviewed until death or 30 June 2012 to determine if clinical MRSA infection developed
We identified 909 patients on routine screening who were entry active surveillance cultures (ASC) negative but acquired MRSA colonisation during their hospitalisation

Summary

Introduction

Patients newly colonised with methicillin-resistant Staphylococcus aureus (MRSA) are at higher risk of clinical MRSA infection. Methicillin-resistant Staphylococcus aureus (MRSA) has become a major cause of hospital-associated infection since emerging in the 1960s. MRSA infection has been associated with many negative outcomes including higher hospital costs, longer hospital stays and higher mortality [2,3]. In Singapore, patients with MRSA infection during admission were 10.2 times more likely to die during hospitalisation, had 4.6 times longer hospital stays and had hospitalisation costs 4.0 times higher than matched uninfected controls [4]. Colonisation with MRSA is a major risk factor for subsequent MRSA infection [6,7,8]. This is well-established for infection occurring in the same admission as MRSA detection, and there is mounting evidence that the risk of MRSA infection may persist for longer periods in some colonised patients [9,10,11,12,13]

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