DIFFICULTIES IN ASSESSING COMMUNITY-ACQUIRED INFECTION AS A RISK FACTOR FOR NOSOCOMIAL INFECTION AT AN INTENSIVE-CARE UNIT

Objective: To analyze the relationship between presentation with a com munity-acquired infection (CAI) and the risk of subsequent nosocomial infection, and the assessment of a likely diagnostic bias in this asso ciation. Design: A prospective cohort study. APACHE II and TISS were u sed to assess severity and therapeutic intensity, respectively. Nosoco mial infection (NI) was diagnosed according to SENIC and CDC diagnosti c criteria. The relative risk and its 95% confidence interval were est imated. Setting: The intensive care unit (ICU) of the University of Gr anada Hospital (Spain). It is a ten-bed multidisciplinary unit. Patien ts: 448 patients admitted to the intensive care unit (ICU) between Dec ember-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 pre vious infection acted as a preventive factor in patients admitted to t he 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 longe r stay at ICU before a NI was diagnosed and they remained at ICU longe r. In multivariate analysis the NI risk in patients with a CAI compare d with those not infected previously and controlling for other variabl es was of 0.36. Conclusion: The presence of a CAI may introduce a diff erential information bias in the study of NI.