Techniques were developed and tested for sampling unbaited domestic flies both outdoors and indoors to determine the natural occurrence of Shigella organisms. A total of 65,273 flies collected outdoors yielded 69 isolations of Shigella and 5,664 flies collected indoors yielded 12 isolations of Shigella.
Comparison of rate of isolations from flies with rate of recovery by the rectal swab technique indicated that the indices from flies generally paralleled the indices from humans, but that they were too low to provide a sufficiently sensitive and effective means of measuring Shigella prevalence. Sampling of flies might be used to advantage in certain situations where high fly populations or high Shigella prevalence occurs.
Eleven different types of Shigella were isolated from flies and the same 11 types were isolated from human sources. Associations in time, location, and Shigella type were noted.
Musca domestica was the most abundant species of fly collected and most common in Shigella-positive fly pools; Ophyra spp. were second in abundance. Major fly attractants were found to be human excrement, scattered garbage, and waste wash water.