Burden of meticillin-resistant Staphylococcus aureus colonization and infection in London acute hospitals: retrospective on a voluntary surveillance programme

Although meticillin-resistant Staphylococcus aureus (MRSA) is recognized as an important cause of hospital and community healthcare-associated morbidity, and colonization as a precursor to infection, few studies have attempted to assess the burden of both colonization and infection across acute healthcare providers within a defined health economy. This study describes the prevalence and incidence of MRSA colonization and infection in acute London hospital Trusts participating in a voluntary surveillance programme in 2000-2001. Hospital infection control staff completed a weekly return including details on incident and prevalent colonizations, bacteraemias and other significant infections due to MRSA. Incidence and prevalence rates were calculated for hospitals with sufficient participation across both years. Colonizations accounted for 79% of incident MRSA cases reported; 4% were bacteraemias, and 17% other significant infections. There was no change in incidence of colonization of hospital patients between 2000 and 2001. By contrast, there was an unexplained 49% increase in prevalence of colonizations over this period. For any given month, prevalent colonizations outnumbered incident colonizations at least twofold. This MRSA surveillance programme was unusual for prospective ascertainment of incident and prevalent cases of both colonization and infection within an English regional health economy. Consistent with other studies, the incidence and prevalence of colonization substantially exceeded infection. Given the small contribution of bacteraemias to the overall MRSA burden, and the surveillance, screening and control interventions of recent years, it may be appropriate to review the present reliance on bacteraemia surveillance.