Incidence of bacteremia at the time of ICU admission and its impact on outcome

Introduction

Blood culture is routinely taken at the time of admission to the ICU for all patients suspected to have any infection, even though it may be positive only in a few patients. Moreover, the impact of a positive blood culture in such a patient population is not clear.

Objective

To find the incidence of bacteremia at the time of ICU admission, to assess its impact on the outcome, and to analyze which factors are related to poorer outcomes in these bacteremic patients.

Methods

A retrospective cohort study over a 2-year period. Data from all the admissions to a medical ICU, in a tertiary care hospital, with suspected infection in whom blood cultures were sent at the time of admission were analyzed. Data regarding patient demographics, probable source of infection, previous antibiotic use, and ICU course were recorded. Severity of illness on admission was assessed by APACHE II score. Qualitative data were analyzed using the chi-square test or Fisher exact test and quantitative data were analyzed using Student's t test. Primary outcome measure was ICU mortality.

Results

A total of 567 patients were included in the analysis. A significant proportion of these patients, 238/567 (42%), were already on antibiotics. Three hundred and sixty-three (64%) patients were direct ICU admissions from casualty, 61 (10.76%) were shifted from hospital wards, 35 (6.17%) from other ICUs in the hospital, and 108 (19.05%) were transfers from other hospitals. Blood cultures were positive in only 60/567 patients (10.6%). Mortality was significantly higher in patients with positive blood cultures (27/60, 45% vs. 69/507, 13.6%; P = 0.000). Univariate analysis for assessing the risk factors for ICU mortality among bacteremic patients was done in which age (P = 0.061), sex (P = 0.253), type of admission (P = 0.203), type of organism, severity of illness (P = 0.234), and site of infection (P = 0.250) were analyzed, but only previous antibiotic use was statistically associated with higher mortality (P = 0.011). Bacteremic patients who were already on antibiotics had a significantly higher mortality (54.2% vs. 8.3%) (OR 12.9, 95% CI: 1.6 to 100). Mortality was higher in patients with Pseudomonas bacteremia (72.7%) although it was not statistically significant (P = 0.08). See Tables 1 and 2.

Table 1 abstract P41

Table 2 abstract P41

Conclusions

Blood cultures may be positive in only a minority of patients with suspected infection admitted to the ICU as most of these patients may already be taking antibiotics. Nevertheless, the prognosis of those patients with positive blood culture is worse, especially if culture is positive in spite of the patient being on antibiotics.