Objective: To analyze the relationship between presentation with a community-acquired infection (CAI) and the risk of subsequent nosocomial infection, and the assessment of a likely diagnostic bias in this association.
Design: A prospective cohort study. APACHE-II and TISS were used to assess severity and therapeutic intensity, respectively. Nosocomial infection (NI) was diagnosed according to SENIC and CDC diagnostic criteria. The relative risk and its 95% confidence interval were estimated.
Setting: The intensive care unit (ICU) of the University of Granada Hospital (Spain). It is a ten-bed multidisciplinary unit.
Patients: 448 patients admitted to the intensive care unit (ICU) between December-1986 and April-1988 who stayed at the ICU for at least 24 hours were included in the study.
Results: The crude analysis suggests that CAI may prevent NI. When data were stratified by other variables a previous infection acted as a preventive factor in patients admitted to the ICU from emergency room, in patients with lower severity level and in those with shorter stay lengths at ICU. Patients with a CAI showed higher severity; they were treated more aggressively, they had a longer stay at ICU before a NI was diagnosed and they remained at ICU longer. In multivariate analysis the NI risk in patients with a CAI compared with those not infected previously and controlling for other variables was of 0.36.
Conclusion: The presence of a CAI may introduce a differential information bias in the study of NI.