Abstract
BackgroundDespite a substantial burden of non-bacteraemic methicillin resistant Staphylococcus aureus (MRSA) disease, most MRSA surveillance schemes are based on bacteraemias. Using bacteraemia as an outcome, trends at hospital level are difficult to discern, due to random variation. We investigated rates of nosocomial bacteraemic and non-bacteraemic MRSA infection as surveillance outcomes.Methods and FindingsWe used microbiology and patient administration system data from an Oxford hospital to estimate monthly rates of first nosocomial MRSA bacteraemia, and nosocomial MRSA isolation from blood/respiratory/sterile site specimens (“sterile sites”) or all clinical samples (screens excluded) in all patients admitted from the community for at least 2 days between April 1998 and June 2006. During this period there were 441 nosocomial MRSA bacteraemias, 1464 MRSA isolations from sterile sites, and 3450 isolations from clinical specimens (8% blood, 15% sterile site, 10% respiratory, 59% surface swabs, 8% urine) in over 2.6 million patient-days. The ratio of bacteraemias to sterile site and all clinical isolations was similar over this period (around 3 and 8-fold lower respectively), during which rates of nosocomial MRSA bacteraemia increased by 27% per year to July 2003 before decreasing by 18% per year thereafter (heterogeneity p<0.001). Trends in sterile site and all clinical isolations were similar. Notably, a change in rate of all clinical MRSA isolations in December 2002 could first be detected with conventional statistical significance by August 2003 (p = 0.03). In contrast, when monitoring MRSA bacteraemia, identification of probable changes in trend took longer, first achieving p<0.05 in July 2004.ConclusionsMRSA isolation from all sites of suspected infection, including bacteraemic and non-bacteraemic isolation, is a potential new surveillance method for MRSA control. It occurs about 8 times more frequently than bacteraemia, allowing robust statistical determination of changing rates over substantially shorter times or smaller areas than using bacteraemia as an outcome.
Highlights
Staphylococcus aureus is responsible for a substantial burden of nosocomial disease; for example, being named in 8% of hospital discharge diagnoses in a recent study in the United States[1]
In the UK, which has had a large outbreak of two clones of methicillin-resistant S. aureus (MRSA) for the last fifteen years, methicillin resistant Staphylococcus aureus (MRSA) accounts for 37% of S. aureus blood stream isolates[2], with evidence that it has added to the burden of disease caused by methicillin sensitive S. aureus[3]
Repeated isolation of MRSA from different clinical samples from a single patient is common; to estimate the number of infections, we determined the first clinical isolation (FCI) of MRSA for each patient admitted between 1 April 1998 and 1 July 2006, initially considering all clinical samples. 8% of FCIs .2 days after admission were from blood, with 15% from other normally sterile locations, 10% from respiratory samples, 59% from surface cultures, and the remaining 8% from urine specimens, a total of 3450 FCIs (Table 1)
Summary
Staphylococcus aureus is responsible for a substantial burden of nosocomial disease; for example, being named in 8% of hospital discharge diagnoses in a recent study in the United States[1]. MRSA bacteraemia is a serious outcome, amendable to passive surveillance; it is recognised that monitoring using bacteraemia rates necessitates long periods of follow-up to determine whether infection control interventions have had an effect in a hospital or hospital subunit[5]. Carriage of Staphylococcus aureus is a well-recognised precedent of infection with the same strain[6], and multiple studies show MRSA isolation from diverse sites, including ulcers, is associated with high risk of subsequent clinical infection[7,8,9]. Isolation of S. aureus is common with ventilator associated pneumonia[10] and surgical site infections[11]: for both, MRSA increases morbidity, hospital stay and costs relative to methicillin sensitive strains[12,13,14,15]. Despite a substantial burden of non-bacteraemic methicillin resistant Staphylococcus aureus (MRSA) disease, most MRSA surveillance schemes are based on bacteraemias. We investigated rates of nosocomial bacteraemic and non-bacteraemic MRSA infection as surveillance outcomes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
