In the 1990s, a study found that Escherichia coli bacteria can proliferate in and on the mouthparts of house flies.
In 2021, for instance, a study found that house flies infected with Chlamydia tachomatis could keep this pathogen alive in their crop for 24 hours – plenty of time to fly off and regurgitate on a new host."While there is little doubt that flies can carry bacteria, viruses, and parasites from waste to our food, a single touchdown is unlikely to trigger a chain reaction leading to illness for the average healthy person," University of Sydney entomologist Cameron Webb wrote in 2015.