Occurrence of methicillin-resistant Staphylococcus aureus infections in German intensive care units

Background: This study aims to describe the occurrence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infections and the relation between endemic and epidemic nosocomial MRSA infections in intensive care units (ICUs) in Germany. Methods: The ICU component within the German national nosocomial infections surveillance system (KISS) was established in January 1997. The number of participating ICUs increased from 25 in 1997 to 178 (June 2000). In every case of nosocomial infection (NI), the pathogens identified were referred to the surveillance system. To identify clusters and outbreaks and distinguish them from mere single events, the following simple definitions were applied: a "cluster" was two nosocomial MRSA infections within 3 months; an "outbreak" was three or more nosocomial MRSA infections within 3 months; all other MRSA infections were classed as "single events." Results: A total of 10,261 NIs were identified during the observation period in the 139 ICUs which had been participating for at least 6 months. Among the 1,535 nosocomial S. aureus infections, 219 MRSA infections were identified (14.3%). Only 51 (36.7%) of the 139 KISS ICUs identified nosocomial MRSA infections. In 12 ICUs (8.6%) however, more than 50% of all nosocomial S. aureus infections were caused by MRSA. The mean incidence density was 0.31 nosocomial MRSA infections/1,000 patient days (range 0-3.6). Outbreaks were registered in 13 ICUs, clusters in 12 further ICUs and only single events in the remaining 26. 64.0% of all MRSA infections were registered during outbreaks and 12.8% in cluster situations. Thus, only 23.2% of MRSA infections were single events. Conclusion: These definitions of clusters and outbreaks can only provide an estimate of the real number of cases. However, through the targeted identification of ICUs with endemic and epidemic MRSA problems and subsequent strict measures to prevent the spread of MRSA within these ICUs, it may be possible to retain, or even reduce, the present Level of MRSA infections in Germany.