CreditBrittany Greeson for The New York Times
Residents of Flint, Mich., affected by the contaminated-water crisis have added a new complication to their lives: an outbreak of shigellosis, a bacterial illness that is easily transmitted when people do not wash their hands.
Health department officials in Genesee County, where Flint is the largest city, said there has been an increase in the gastrointestinal illness, which can lead to severe diarrhea, fever, nausea, vomiting, cramps and stools containing blood and mucus, according to a statement issued last month.
From the beginning of the year through the week ending Oct. 1, that county had 85 cases, the highest number in the state, according to the latest data from the Michigan Department of Health and Human Services.Neighboring Saginaw County was next, with 49 cases.
The number of cases of shigellosis ((pronounced she-guh-LO-sis) throughout the state has totaled 454 so far this year. There were 515 cases of the food-borne illness in all of 2015, and 309 cases in 2014.
“Shigella cases are on the rise across Michigan,” the county health department statement said.
According to the Centers for Disease Control and Prevention, shigellosis affects 500,000 people in the United States every year. It is transmitted through the accidental ingestion of fecal matter containing the bacteria, such as when food handlers do not wash their hands.
Trust in Flint’s water has been severely low since a lead-contamination crisis after residents raised the alarm over the foul odor and rusty appearance of their water. A decision by officials in 2014 to switch the city’s water source to the Flint River from Lake Huron was suspected in health problems like rashes and hair loss, and symptoms in children including weight loss and problems with coordination.
The city later switched the water source back, but in July, state prosecutors filed criminal charges against six government workers, accusing them of concealing information about the lead contamination and doing nothing to stop it. The charges brought to nine the number of government employees implicated, but residents have expressed outrage that high-ranking officials have so far escaped any consequences.
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.”