Flies, especially houseflies, are widely recognized as potential reservoirs and vectors of foodborne Salmonella pathogens. In this study, flies were collected at caged-layer facilities that had produced eggs that were implicated as the food vehicle in two recent outbreaks of Salmonella Enteritidis infections. The flies were separated by species into pools for microbiological testing. A total of 15 species pools of houseflies, Musca domestica L., and 7 species pools of bronze dump flies, Hydrotaea aenescens (Wiedemann) (Diptera: Muscidae), were analyzed. Salmonella Enteritidis was isolated from 2 of the 15 pools of houseflies. Other species of Salmonella were isolated from three pools of flies, including Salmonella Infantis from houseflies and from dump flies and Salmonella Heidelberg from houseflies. Salmonella Mbandaka was isolated from a lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae).

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Forty-seven species of flies have been reliably associated with filthy conditions that might allow the spread of foodborne pathogens. These are categorized as "filth flies." Of that 47, only 21 species represent a potential threat to human health as scientifically proven causative agents of foodborne myiasis or as carriers of enteropathogenic Escherichia coli, Salmonella, Shigella, and other foodborne pathogens. These 21 species are categorized as "disease-causing flies" based on strict scientific criteria. The criteria are association with E. coli, Salmonella, AND Shigella; synanthropy; endophily; communicative behavior; attraction to both excrement and food products; and recognition by authorities as a potential health hazard. Within Hazard Analysis and Critical Control Point and other U.S. Food and Drug Administration regulatory frameworks, disease-causing flies are contributing factors to the spread of foodborne disease that require preventive and corrective actions as appropriate under Sanitation Standard Operating Procedures, Good Manufacturing Practices, or pest control programs.