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SIR Study

SIR1-Study - (Study of Representativity of the KISS- und SARI-Data)

Funding: funded by BMBF up to Dec 31, 2005

Principal investigator:  Prof. Dr. Martin Schumacher (IMBI)

Study statisticians: Prof. Dr. Martin Schumacher (IMBI), Dipl.-Math. Gerta Rücker (IMBI)



Data routinely collected within the German nosocomial infection surveillance system KISS are recommended as reference data for judging nosocomial infection rates in German intensive care units (ICUs). The SIR1 study (1) was designed to estimate unbiased incidence rates of nosocomial infections in interdisciplinary German ICUs and to examine whether the KISS data are representative. Methodological issues include stratified random sampling of German ICUs, investigation of seasonal effects, statistical modeling of incidence rates, and comparison of weighted incidence rates obtained by KISS and the SIR1 study with the standardized rate ratio. Within the SIR1 study, 50 randomly selected ICUs were observed for two consecu-tive months each, corresponding to 21832 patient days, during which 262 infections occurred. All analyses were adjusted for hospital size. In order to account for potential over-dispersion due to differences between ICUs, we fitted a negative binomial regression model.2 Since we did not find any seasonal trend in the KISS data from two consecutive years, we did not consider month of data collection in the SIR1 study as a potential confounder. The incidence rates provided by the SIR1 study are on average (standardized rate ratio) 1.89 (95% confidence interval 1.63-2.20) times as large as those estimated by the KISS system.3 Additionally, device-associated infection incidence rates were estimated. The study provides evidence that the KISS surveillance system tends to under-estimate the true incidence rates of nosocomial infections in German ICUs.