Abstract

Background. Estimating the burden of intestinal colonization with antibiotic-resistant gram-negative bacteria (AR-GNB) is critical to understanding their global epidemiology and spread. This study aimed to determine the prevalence of, and risk factors for, intestinal colonization by AR-GNB in both hospital-based and community-based populations in Chile. Methods. Between December 2018 and May 2019, we enrolled randomly selected hospitalized adults from four tertiary-care public hospitals (Antofagasta, Santiago, Curicó, and Puerto Montt), and adults from a rural community-based cohort in Molina. After obtaining informed consent, we collected rectal swabs and epidemiological data using a standardized questionnaire. Swabs were cultured on MacConkey agar supplemented with 2 µg/mL ciprofloxacin or ceftazidime. All morphotypes were identified, and antibiotic susceptibility testing was performed using disk diffusion. The primary outcome was the prevalence of colonization with fluoroquinolone (FQ)- or third-generation cephalosporin (3GC)–resistant GNB. The secondary outcome was colonization with multidrug-resistant (MDR) GNB, defined as resistance to ≥3 antibiotic classes. Bivariate and multivariate analyses were performed to identify risk factors for colonization. Results. A total of 775 hospitalized patients (median age: 60 years, IQR 42–72) and 357 community participants (median age: 55 years, IQR 48–62) were enrolled. Among hospitalized patients, the prevalence of colonization with FQ- and 3GC-resistant GNB was 47% (95% CI, 43%–50%) and 41% (95% CI, 38%–45%), respectively. MDR-GNB colonization prevalence was 27% (95% CI, 24%–31%). In the community, colonization with FQ-resistant, 3GC-resistant, and MDR-GNB was 40% (95% CI, 34%–45%), 29% (95% CI, 24%–34%), and 5% (95% CI, 3%–8%), respectively. Independent risk factors for MDR-GNB colonization in hospitalized patients included: hospital of admission, hospitalization unit (highest in ICUs), in-hospital antimicrobial exposure, comorbidities (Charlson index), and length of stay. In the community, recent antibiotic use (<3 months) was a predictor of colonization with FQ- or 3GC-resistant GNB, while alcohol consumption was inversely associated with MDR-GNB colonization. Conclusions. This study reveals a high burden of AR-GNB colonization among both hospitalized and community-dwelling adults in Chile. The notable prevalence of FQ- and 3GC-resistant GNB in the community suggests it may be an underrecognized reservoir for antibiotic resistance. Further investigations are needed to explore the genetic relatedness of resistant strains circulating between the hospital and community settings.