Airborne transmission of Salmonella enteritidis infection between groups of chicks in controlled-environment isolation cabinets

Although direct contact with infected birds and indirect contact with contaminated environmental surfaces are known to be important factors in the dissemination of Salmonella enteritidis in poultry flocks, the potential role of airborne transmission is less clearly defined. This study considered the mechanism by which S. enteritidis might spread between groups of chicks housed in controlled-environment disease transmission cabinets, separated by an unoccupied space that prevented any direct or indirect contact. Airflow in these cabinets was directed across the unoccupied area from one ("upstream") group of chicks to the other ("downstream") group. In each of four replicate trials, two groups of 25 chicks were placed in the upstream ends of transmission cabinets and orally inoculated with S. enteritidis at 1 week of age. One day later, 25 1-day-old chicks were placed in the downstream end of each cabinet. When chicks were removed and sampled at 3 and 7 days postinoculation, S. enteritidis was found on the feathers of 77% of the downstream chicks. Moreover, 33% of the downstream chicks became infected with S. interitidis. The comparative frequencies of recovery of S. enteritidis from various downstream sampling sites suggested that infection was apparently transmitted principally by oral ingestion, perhaps from environmental surfaces contaminated by airborne movement of the pathogen. Reducing the airborne movement of S. enteritidis in poultry houses should thus help limit the spread of infection within flocks and thereby diminish the incidence of production of contaminated eggs.