Air exposure as a possible route for ESBL in pig farmers

Abstract

Introduction: Livestock can carry extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, with CTX-M-1 ESBLs as the most important enzyme representatives. ESBL carriage in farmers is associated with ESBL carriage in animals which is frequently thought to originate from direct animal-human contact. However, inhalation of stable air might represent a second route of transmission. We investigated the presence of ESBL genes belonging to blaCTX-M group 1 (CTX-M-1gr) in dust and the association with CTX-M-1gr carriage in pig farmers, family members and employees. Methods: 146 people living and/or working on 34 conventional Dutch pig production farms (farmers, family members and employees) were enrolled. Human stool samples, rectal swabs from 60 pigs per farm, and 2-5 passively sampled dust samples (as a proxy for presence of viable CTX-M-1gr carrying bacteria in air) per farm were obtained during two sampling moments with a 12-month interval. Presence of ESBL-producing E. coli in stool samples and rectal swabs was determined by selective plating and CTX-M-1gr was identified by PCR. Dust samples were analyzed directly by PCR for presence of CTX-M-1gr. Questionnaires were used to collect information on intensity and duration of animal contact. Results: Overall human prevalence of CTX-M-1gr carriage was 3.6% and CTX-M-1gr carrying pigs were present on 30% of the farms. CTX-M-1gr was detected in dust on 21% of the farms. Human CTX-M-1gr carriage and presence of CTX-M-1gr in dust were associated univariately (OR=11.9, 95% CI=2.6-55.4). In multivariate analysis human CTX-M-1gr carriage was associated with working hours per week (OR=1.03, 95% CI=1.00-1.06), presence of CTX-M-1gr carrying pigs on the farm (OR=7.3, 95% CI=1.1-48.8) and presence of CTX-M-1gr in dust (OR=3.5; 95% CI=0.6-20.7). Conclusions: Transmission of CTX-M-1gr from animals to human might be possible through air, pending verification of the presence of viable ESBL producers in air.