Background: We have not found any study assessing the sensitivity of different frequencies of nosocomial infection surveillance (NIS). The objective of this study is to contribute to the ascertainment of the frequency of the NIS surveillance in surgical patients, where NIS has shown to be most efficient.
Methods: A prospective cohort study on 1,483 patients undergoing general surgery in a reference hospital was performed between November 1992 and July 1994. A daily NIS, plus review of clinical chart after hospital discharge, performed by two trained clinicians was taken as gold standard. The expected number of infections detected according to different schedules of NIS (from a minimum of weekly examination to a NIS performed every other day) was estimated taking into account the duration of infection and the hospital stay after infection healing. This number was corrected multiplying it by 0.9 (sensitivity of NIS without reviewing clinical chart after discharge). Confidence intervals (CI) were estimated using the binomial's exact method.
Results: 235 nosocomial infections were detected by the gold standard. The sensitivity of the weekly NIS for all infections was 78.3% (95% CI = 72.5-83.4); it varied from 63.6% (95% CI = 45.1-79.6) for urinary tract infections (UTI) to 85% (95% CI = 62.1-96.8) for respiratory tract infections; for surgical wound infections, it was 80.1% (95% CI = 72.4-86.5). As expected sensitivity increased with the frequency of NIS. A frequency of NIS every four days yielded a sensitivity for all infections of 86.4% (IC 95% = 81.3-90.5), 78.8% (CI 95% = 61.1-91.0) for UTI and 86.8% (CI 95% = 79.9-92.0) for SWI.
Conclusions: Most nosocomial infections were detected by one visit a week. Twice visits a week improved the sensitivity of NIS in about 10%. It is important to emphasize that results change according to duration of infection and post-discharge hospital stay.