Significant reduction of endemic MRSA acquisition and infection in cardiothoracic patients by means of an enhanced targeted infection control programme

Summary

Due to increasing methicillin-resistant Staphylococcus aureus (MRSA) infection in cardiothoracic patients at St Thomas' Hospital, an enhanced infection control programme was introduced in September 2000. It was based on UK national guidelines on the control of MRSA and targeted additional identified risk factors for surgical site infection (SSI). It included recognition of the problem by senior staff and their taking responsibility for it; intensive support, education and advice from the infection control team; improved ward and theatre hygiene; pre-admission, admission and weekly MRSA screening; isolation and clearance treatment; nursing care pathways for MRSA colonized patients; and teicoplanin plus gentamicin surgical prophylaxis. The effectiveness of the programme was assessed by retrospective analysis of computerized patient data for the 16 months before and after the introduction of the programme. There was no significant change in the number of operations or the proportion of patients admitted with MRSA, although nine patients were cleared of carriage before admission. However, there were significant falls in the proportion of patients acquiring MRSA on the ward [38/1036 to 14/921, P=0.003, RR 2.4 (95%CI 1.32–4.42)] and in the rate of bloodstream MRSA infections [12/1075 to 2/956, P=0.014, RR 5.34 (95%CI 1.20–23.78)]. Sternal and leg wound infections both halved (from 28/1075 to 13/956 and 16/1075 to 7/956, respectively) but this did not reach statistical significance. These results demonstrate that an enhanced, targeted infection control programme based on the UK national guidelines, SSI prevention guidelines and local risk assessment can reduce the incidence of nosocomial MRSA acquisition and invasive infection in cardiothoracic patients in the face of continuing endemic risk.

Introduction

Staphylococcus aureus is still the most common cause of surgical site infection (SSI). S. aureus accounted for 19% of all pathogens isolated from SSIs in the US National Nosocomial Infection Surveillance during 1990–1992,¹ and 37% of isolates in the English Nosocomial Infection National Surveillance Scheme (NINSS) during 1997–1999.² Furthermore, in the UK and in many other countries, methicillin-resistant Staphylococcus aureus (MRSA) are now the dominant cause of staphylococcal wound infection. In the NINSS study in England, 61% of all S. aureus SSI isolates were methicillin resistant.²

SSIs, especially sternal wound infections, are important causes of postoperative morbidity and mortality in cardiac surgery, and are often complicated by bacteraemia.3, 4 It is generally considered that wound infection rates should be less than 3% in coronary artery bypass graft (CABG) surgery;⁵ however, recent measured rates range between about 1% and 10% in both the UK and the USA.1, 2

The control of the present epidemic of MRSA in British hospitals has proved difficult, despite the introduction of revised guidelines.⁶ The Central Public Health Laboratory surveillance reports of S. aureus bacteraemia have shown that the proportion of methicillin-resistant strains of S. aureus isolated from blood has risen from about 1.5% in 1989–1991 to 42% in 1998.7, 8

In our hospital, there was an increase of CABG SSIs during 1999, most of which were associated with MRSA infection and some were complicated by MRSA bacteraemia. Concern over these MRSA infections prompted us to introduce an enhanced programme of MRSA control in cardiothoracic patients. This was based on the 1998 UK guidelines for the control of MRSA and on US guidelines on the control of SSI sepsis and infections in theatres.6, 9 In this paper, we describe the methods we used and show that MRSA acquisition rates and infection rates fell significantly after their introduction.