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 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.