ABSTRACT

This study assessed the levels of two key pathogens, Salmonella and Campylobacter, along with the indicator organism Escherichia coli in aerosols within and outside poultry sheds. The study ranged over a 3-year period on four poultry farms and consisted of six trials across the boiler production cycle of around 55 days. Weekly testing of litter and aerosols was carried out through the cycle. A key point that emerged is that the levels of airborne bacteria are linked to the levels of these bacteria in litter. This hypothesis was demonstrated by E. coli. The typical levels of E. coli in litter were ∼10⁸ CFU g⁻¹ and, as a consequence, were in the range of 10² to 10⁴ CFU m⁻³ in aerosols, both inside and outside the shed. The external levels were always lower than the internal levels. Salmonella was only present intermittently in litter and at lower levels (10³ to 10⁵ most probable number [MPN] g⁻¹) and consequently present only intermittently and at low levels in air inside (range of 0.65 to 4.4 MPN m⁻³) and once outside (2.3 MPN m⁻³). The Salmonella serovars isolated in litter were generally also isolated from aerosols and dust, with the Salmonella serovars Chester and Sofia being the dominant serovars across these interfaces. Campylobacter was detected late in the production cycle, in litter at levels of around 10⁷ MPN g⁻¹. Campylobacter was detected only once inside the shed and then at low levels of 2.2 MPN m⁻³. Thus, the public health risk from these organisms in poultry environments via the aerosol pathway is minimal.

Bacterial aerosols can originate from different sources, each representing a unique aerosol environment. The generation of these aerosols can occur during common agricultural practices such as the spray irrigation of wastewater (13), and the land application of biosolids (7). Biological material in air does not necessarily occur as independent particles (22), and the survival of particulate matter linked bacteria can vary with particle size and prevailing atmospheric conditions (27). In addition to the natural variation of bacteria that occur in the general atmosphere (26), the creation, generation, and disposal of human and animal wastes can increase the potential of microbial pathogens entering the aerosol environment (32). Animal production systems such as broiler farms have been the focus of attention as potential sources of human pathogens entering the general environment and thus eventually the human food chain. Much of this focus has been on the land application of manures (30) rather than via the aerosol pathway.

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