Flies are often considered to be just a nuisance pest, but they are actually vectors of disease and carry risk in food facilities. Illustrating this, McCloud Services Training Manager and Entomologist Anna Berry related the example of a food facility which recently had a Listeria outbreak — for which small flies were discovered to have been the cause. The food facility’s drains had organic material in which both Listeria bacteria and small flies were thriving. “The flies picked up bacteria on their body and transferred it to the equipment and food surfaces, causing food to come into contact with Listeria and creating an outbreak,” Berry explained.
Because small flies typically breed indoors, their presence indicates a sanitation concern that has led to them being in the facility, Berry said. “They’re typically more challenging to control as we need to find that breeding site and eliminate it.” On the other hand, large “filth” flies, such as house flies, typically breed outdoors, she said. So they “are typically indicative of doors/windows being left open or unsealed gaps or holes in the facility.”
Large flies also can be significant disease vectors in food facilities. As Western Pest Services Entomologist and Manager of Innovations & Continuous Improvements Shannon Sked explained, the body of the house fly is covered with hairs that can catch pathogens. When they land on a food surface, they can transmit that bacteria. “Flies feed externally,” he said. “They actually secrete their stomach enzymes out through their mouth, which creates a slurry out of the food, and then sponge them up with their specialized mouthparts.” So whatever pathogens are in their stomach content can end up as a slurry in your food.
To resolve small fly issues, said Rentokil Technical Services Manager and Entomologist Michael Thome, look for areas of decaying organic matter buildup such as drains and sewage access points/lines, equipment and warewashing areas, damaged floors or tiles, and equipment that isn’t cleaned regularly. Hot spots for large flies can be entranceways (loading docks, doors, etc.); dumpster or waste areas; raw meat products and offal; and livestock areas, coops, or animal pens. “Pay close attention to these areas in your facility and ensure that you’re implementing appropriate control measures,” he said.
Because it is so easy for flies to cause outbreaks, regulatory agencies, as well as third-party auditors, have a low threshold for them, Berry said. So fly populations that are left unchecked can result in loss of audit points and facility closure. “This could then have a detrimental effect on the facility’s brand and reputation, and in the end, the food facility’s bottom line.”
A fly issue can trigger an alarm that there is a larger problem, and result in an inspector or auditor looking deeper for conducive issues, Thome said, adding, “With the passage of the Food Safety Modernization Act, regulatory inspectors have greater power to take action if they suspect that food safety is being compromised.”
Additionally, he said, “In today’s 24/7 media world, where just about anyone can publish content, news of a problem at a facility can get out quickly. Cases of sanitation issues being filmed by employees and shared on social media have increased in recent years, leading to unwanted publicity and further brand risk.”
Flies are one of the most prolific breeders of the animal world, Sked said. Their ecological importance is that they break down decaying material, but this also makes them incredible transmitters of pathogens. The World Health Organization (WHO) estimates that flies can transmit at least 65 different diseases, many of which are foodborne pathogens, he said. “So any issue with flies is a red flag to customers, auditors, and the market.”
Originally featured in Quality Assurance & Food Safety.