Residents have been relying on bottled water to drink at home but still recoil from using tap water for other purposes, such as washing and cooking. They have adapted their personal hygiene habits, including where and how they take showers.

Residents are also using baby wipes, which they get free at bottled-water-distribution centers, to clean their hands. But that may be contributing to the current transmission of the shigella bacteria, because they are not chlorinated and do not kill the bacteria.

The C.D.C. and other agencies recommend washing hands with warm, soapy water to avoid transmitting the shigella bacteria, which are also spread through contaminated surfaces, food or water.

A report published in August by the Michigan health department, the C.D.C. and other agencies about rashes in Flint showed that a large percentage of residents had changed their frequency or methods of bathing, using bottled water or water that did not come from the Flint municipal system. About 4 percent of 185 people surveyed said they used baby wipes.

Matt Karwowski, a medical epidemiologist with the C.D.C., said in a telephone interview on Tuesday that outbreaks of shigellosis were not uncommon in the United States, particularly during the summer months. He said there was concern that the outbreak in Genesee could be larger than the usual rate of infection.

“There is definitely some question about whether changes in hand-washing and hygiene practices may be playing a role,” he said. “People in Flint have been concerned about the safety of their water supply, and that may be playing a role in their hygiene practices.”