Air exposure as a possible route for ESBL in pig farmers

Livestock can carry extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, with blac being most prevalent. ESBL carriage in farmers is associated with ESBL carriage in animals, with direct animal human contact considered as the dominant route of transmission. However, inhalation of stable air might represent another route of transmission. We, therefore, quantified presence of bla(CTX-M) group 1 genes (CTX-Mgrl) in dust and the association with CTX-M-grl carriage in pig farmers, family members and employees. We included 131 people living and/or working on 32 conventional Dutch pig production farms (farmers, family members and employees) during two sampling moments over a 12 -month interval. Human stool samples, rectal swabs from 60 pigs per farm, and 2-5 dust samples collected using an electrostatic dust collector (EDC) (as a proxy for presence of viable CTX-M-grl carrying bacteria in air) were obtained per farm. Presence of ESBLproducing Escherichia Coli (E. colt) in stool samples and rectal swabs was determined by selective plating and CTX-M-grl was identified by PCR. Dust samples were analyzed directly by PCR for presence of CTX-M-grl. Questionnaires were used to collect information on nature, intensity and duration of animal contact. Overall human prevalence of CIX-M-grl carriage was 3.6%. CTX-M-grl was detected in dust on 26% of the farms and in pigs on 35% of the farms, on at least one sampling moment. Human CTX-M-grl carriage and presence of CIX-M-grl in dust were associated univariately (OR=12.4, 95% CI=2.7-57.1). In multivariate analysis human CTX-M-grl carriage was associated with the number of working hours per week (OR=1.03, 95% CI=1.00-1.06), presence of CTX-M-grl carrying pigs on the farm (OR=7.4, 95% CI=1.1-49.7) and presence of CTX-M-grl in dust (OR=3.5, 95% CI=0.6-20.9). These results leave open the possibility of airborne CTX-M-grl transmission from animals to humans next to direct contact.