Relationship of microorganism carriage and infections in ICU patients

Introduction

A prospective cohort study was undertaken to determine the usefulness of surveillance cultures to classify ICU infections and to predict the causative agent of ICU-acquired infections.

Methods

A total of 48 community patients (36 men, 11 women, age 50.17 ± 17.974 years, APACHE II score 13.51 ± 6.153) who were expected to stay in the ICU for >5 days were included in this study. Surveillance cultures of the throat and rectum were obtained on admission and thereafter at days 4, 8 and 12 to look for potentially pathogenic microorganisms (PPMs) in order to distinguish the community acquired from those acquired during the ICU stay. The epidemiological data and the alteration of carriage state of the patients during these days were recorded. Total infection episodes were classified into three categories according to the carrier state: primary endogenous infection (PEI), caused by PPMs carried by the patient in surveillance cultures on admission; secondary endogenous infection (SEI), caused by PPMs of the ICU environment, yielded both in surveillance and diagnostic cultures; and exogenous infection (EXI) for those caused by PPMs that did not yield in surveillance cultures. Statistical analysis was made using Pearson χ², paired t test, and ROC curve. P value ≤ a, a = 5%.

Results

On day 4, colonization was detected by throat and rectum surveillance cultures in 81.1% and 75% of patients, respectively (P << 0.05). The most common microorganism isolated in surveillance cultures from the throat was Acinetobacter baumannii (22.9%) and that from the rectum was Escherichia coli (15.7%). A total of 100 infections were described during the patients' ICU stay (length of stay: 26.44 ± 17.95) distinguished in 28 PEI, 44 SEI and 25 EXI. ICU-acquired infections were 69% of cases. The mean day of PEI diagnosis was 6.2 ± 4.7, of SEI was 12.6 ± 8.2 and of EXI was 12.6 ± 7.3. The causative agent could be predicted in 72% of infections. The sixth day was the cutoff point to predict the causative microbial agent from the surveillance cultures (sensitivity 80%, specificity 74.6%). Isolation of A. baumannii in surveillance cultures had a probability of 92.1% to cause infection.

Conclusion

Our data suggest that surveillance cultures may offer useful information to improve hygiene in the ICU, to determine the causative agent of infection and to follow better antimicrobial policy.