Cyclospora
© CDC

Experts are investigating dozens of cyclospora cases in Fort Bend County.

The food-borne intestinal illness is caused by a parasite found in food and water. It's usually spread by produce tainted with feces.

Thirty-six cases have been confirmed by lab tests and eight more are likely cyclospora, according to the Fort Bend County Health Department.

Fort Bend County Health and Human Services experts are working with the CDC to track the source of the outbreak.

CDC experts traveled to Fort Bend County recently to interview dozens of restaurants and grocery stores. They hope to have an answer in the next few weeks.

At last check, at least four cases of cyclospora have been confirmed in Harris County.

A nationwide outbreak of cyclospora has sickened hundreds of people nationwide.

The CDC traced illnesses from Iowa and Nebraska to salad mix from a Mexican farm that was served at Olive Garden and Red Lobster restaurants.

The rest of the illnesses - many of them in Texas - are still a mystery, state and federal officials say.

The source of this outbreak has proved particularly hard to trace. Doctors have to test specifically for cyclospora and many don't because it is relatively rare. So they may not order the correct tests, at least not at first. The parasite is so tiny that it's often difficult to confirm that a person has the illness, according to the Centers for Disease Control and Prevention. Tests often have to be repeated with fresh samples.

Doctors or labs may not notify state health departments as quickly as they would for a more common foodborne illness like salmonella. And there are different rules in different states about whether cyclospora has to be reported to federal health authorities.

All those obstacles are making it harder for state and federal officials. It also means there are probably many people who have the disease and don't know it.

The illness is rare - roughly 150 cases are reported in the United States annually. Scientists only identified it in the early 1990s.

In comparison, there are tens of thousands of lab-confirmed cases of salmonella food poisoning in this country each year, and officials believe there are hundreds of thousands more that are not confirmed.

The cyclospora parasite is native to the tropics and tends to come into the United States on imported produce. For example, Guatemalan raspberries were the source of five outbreaks in Canada and the United States in the late 1990s. Two of those outbreaks involved more than 1,000 illnesses each, said Ynes Ortega, a cyclospora expert at the University of Georgia.

Officials say part of the problem is that the disease takes a week on average to show up, and diagnosis has often been delayed, making it hard for victims to remember what they ate.

CDC spokeswoman María-Belén Moran says the agency also is interviewing people who aren't sick as controls to get more information on eating patterns, as well as lab testing foods that they suspect.

Food often goes through several stops - potentially in several countries - before it reaches a grocery cart, and trying to trace it is "labor-intensive and painstaking work, requiring the collection, review and analysis of hundreds and at times thousands of invoices and shipping documents," the FDA said.

Symptoms usually show up within seven days of exposure. The most common symptoms include: watery diarrhea; loss of appetite; weight loss; cramping; bloating; increased gas; nausea; fatigue.

Less common symptoms of cyclosporiasis include: vomiting; and low-grade fever.

Without treatment, symptoms can persist for several weeks. The infection usually is not life threatening.

No deaths have been reported in the recent outbreak.