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The importance of distinguishing between bacterial colonisation versus infection in assessing risk factors

Abstract number: 1134_04_198

Tacconelli E., Cataldo M.A., Manno D., De Angelis G., Fadda G., Cauda R., D’Agata E.M.C.

Objective:  

The majority of published studies use infection or clinical cultures as the outcome of interest when assessing risk factors for antimicrobial-resistant pathogens. We hypothesize that risk factors differ between colonization and infection.

Methods:  

Patients with Pseudomonas aeruginosa (PA) bloodstream infections (BSI) were identified during a prospective surveillance study (2002–2004) in a large University hospital, and pts with and without PA rectal colonization, respectively, were identified from a cross-sectional rectal screening of 1036 hospitalized pts. Two case-control studies were performed which included 87 randomly selected pts with PA-BSI (group-1), 29 with PA positive rectal screening (group-2) and 87 randomly selected pts with negative rectal screening (group-3). Exclusion criteria for group-2 and -3 were the detection of a clinical culture positive for PA during hospitalization.

Results:  

Mean age ±SD of population was 58 ± 16 in group-1 and 66 ± 8 y.o. in group-2 (P = ns vs group-3) while the mean length of hospitalization before entering the study was 27 ± 44 in group-1 (P < 0.01) and 35 ± 37 in group-2 (P < 0.01). Resistance to the following drugs was detected more frequently among infecting than colonising strains: imipenem (28% vs 24%, P = ns), ciprofloxacin (55% vs 24%, P < 0.01), ceftazidime (32% vs 31%, P = ns), gentamicin (26% vs 17%, P = ns) , and piperacillin (18% vs 10%, P = ns). Multidrug resistance (2 classes of drugs) was reported in 50% of PA in group-1 vs 27% in group-2 (P = 0.04). At multivariate regression analysis, prolonged length of hospitalization (>17 days; group-1, OR = 2.8; group-2, OR = 3.7) and previous use of cephalosporins (group-1, OR = 6.9; group-2, OR = 9.3) and aminoglycosides (group-1, OR = 35.1; group-2 OR = 12.4) were independent risk factors for both PA colonisation and BSI (P < 0.05). Patients with PA-BSI had a higher Charlson score (>3; OR = 20.5) and were more likely to have had a ICU admission (OR = 5.8) and quinolones therapy within 30 days (OR = 4.3) (P < 0.01). The presence of wheel chair or bed-bound status was independently associated with PA colonisation (OR = 10.6, P < 0.01) but not with BSI.

Conclusion:  

This study provides novel information that may be used to better design future case-control or cohort studies analysing the epidemiology of antibiotic-resistant infections. Taking into consideration the differences between colonization or infection as the outcome of interest may reduce bias and help better design hospital interventions.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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