INDIANAPOLIS, IND. (WOWO) More than 11,000 cases of cyclosporiasis are suspected nationwide as health officials continue investigating a widespread outbreak that has impacted dozens of states, including Indiana.

The Centers for Disease Control and Prevention reported that 4,173 confirmed cases across 41 states have been linked to the ongoing outbreak. However, public health officials warn the actual number of infections is likely much higher because many people who become ill do not seek medical care or testing.

The U.S. Food and Drug Administration is investigating multiple illness clusters connected to the outbreak, including one cluster associated with Taylor Farms lettuce, according to federal health officials.

The FDA said the investigation has identified links to at least five states: Indiana, Michigan, Ohio, West Virginia and Kentucky.

Michigan and Ohio account for the largest share of reported illnesses. The CDC said those states make up the majority of the more than 12,000 cyclosporiasis cases reported nationwide this year.

Michigan has seen an unusually sharp increase, with health officials reporting 7,171 cases as of Wednesday, an increase of more than 1,000 cases since Monday. The state typically records only about 50 confirmed cases of cyclosporiasis annually.

Indiana has also experienced a significant increase, with health officials reporting more than 500 cases as part of the nationwide surge.

Other states reporting elevated case numbers include North Carolina, which has surpassed 500 cases, and Kansas, which has reported more than 280 cases.

Cyclosporiasis is an intestinal illness caused by the parasite Cyclospora cayetanensis. The infection is often associated with contaminated food or water.

Symptoms can include prolonged diarrhea, stomach cramps, nausea, loss of appetite, weight loss, and fatigue. The illness is sometimes described by health officials as causing “explosive diarrhea” because of the severity of symptoms some patients experience.

Although symptoms can be serious, not everyone infected requires hospitalization, and many cases may never be confirmed because patients do not seek testing.

Health officials say that underreporting is a significant challenge during outbreaks because confirmation requires specialized laboratory testing.

The CDC and FDA continue working to determine the source of the outbreak.

While lettuce from Taylor Farms is one area being investigated, federal officials have not identified a single confirmed cause for all reported illnesses.

A Nexstar review of CDC data, state health reports and local reporting found that nearly every state has reported at least one case of cyclosporiasis this year.

Some reported cases, however, have not been connected to the current outbreak investigation.

Health officials in Utah previously reported a resident diagnosed with cyclosporiasis had no known connection to the outbreak.

In Hawaii, state officials said a traveler from a state experiencing recent cases tested positive for cyclosporiasis, but investigators determined the infection was not acquired in Hawaii. The state has not recorded a locally acquired case of cyclosporiasis in the past decade.

Federal outbreak investigators say all but nine states have reported confirmed cases associated with the broader investigation. Those states are:

• Delaware
• Hawaii
• Maine
• Montana
• New Mexico
• Oregon
• South Carolina
• South Dakota
• Vermont

Officials caution that the absence of confirmed outbreak-linked cases in those states does not necessarily mean residents have not become sick.

Cyclosporiasis is classified as a nationally notifiable condition in 47 states, Washington, D.C., and New York City, meaning health departments track and report cases to help identify outbreaks and monitor public health trends.

Health officials continue advising people who develop symptoms consistent with cyclosporiasis to contact a healthcare provider, particularly if symptoms persist or become severe.