Cross-transmission of nosocomial pathogens in an adult intensive care unit: incidence and risk factors.

The incidence and determinants of cross-transmission in an adult intensive care unit (ICU) were examined under normal conditions. Four hundred and thirty patients were followed for 3947 patient-days. Cross-transmitted pathogens were identified by genetic typing. A cross-transmission episode was defined as when two or more patients had indistinguishable isolates and had been treated in the ICU during intervals up to seven days apart. The direction of cross-transmission was confirmed if the incriminated pathogen was isolated from the donor before admission of the recipient; otherwise, both patients could potentially be a donor or a recipient. These patients were excluded from the risk factor analysis. Recipients of pathogens were compared with those who were not involved in cross-transmission. Out of 22 056 examined specimens, 275 isolates were typed and 40 episodes of cross-transmission were detected. The overall incidence of cross-transmission was 10.7 [95% confidence intervals (CI) 7.6-14.5] per 1000 patient-days. In multivariate analysis, those who were nursed in an understaffed environment [odds ratio (OR) = 3.3, 95% CI 1.4-7.8], had a nasogastric tube (OR = 2.9, 95% CI 1.1-7.8) and were ventilated (OR = 2.5, 95% CI 1.1-6.0) for all of their stay, compared with none or part of their stay, showed an increase in the risk of cross-transmission. Repeated bronchoscopy (OR = 5.1, 95% CI 1.04-25) compared with no bronchoscopy and immunosuppresion (OR = 3.9, 95% CI 1.2-12.5) also increased the risk. This study showed that cross-transmission of nosocomial pathogens in the ICU is associated with understaffing, immunosuppression and factors that result in multiple staff/patient contacts, thus emphasizing the importance of hand hygiene.