Cases of the intestinal illness cyclospora continue to spread around the country, the US Centers for Disease Control and Prevention (CDC) reported Friday, adding several new states and New York City to the growing list of places where the infection has been documented.

The source of the widespread outbreak of cyclospora is still unknown as reports of the infection spread to 15 US states

The most current data from the CDC indicates the organization has been notified of at least 321 cases of the stomach bug, including 18 people who have been hospitalized across three states.

Earlier this week the CDC reported cyclospora cases in Iowa, Nebraska, Texas and Wisconsin. The range of the infection has spread to at least nine other states and New York City. Florida, Missouri and Arkansas have been added to the list of states that have notified the CDC of cyclospora infection, which also includes Georgia, Connecticut, New Jersey, Minnesota and Ohio.

Illinois and Kansas have each reported one confirmed case, but it is possible that the patients may have acquired the infection while out of state.

To date, the CDC has confirmed 33 cases of cyclospora infection in official CDC laboratories.

Cyclospora is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis.

People may become infected with cyclospora after consuming food or water contaminated with the parasite, according to the CDC. The Food and Drug Administration (FDA) reports the parasite is unlikely to be transmitted from one person to another, which suggests that those infected consumed a contaminated food or beverage.

Barbara Herwaldt, a CDC medical epidemiologist, said previous cyclospora outbreaks have been traced to produce such as raspberries, basil, lettuce and snow peas, but as of now no specific food has been identified as the source of the outbreak.

It remains unclear whether each of the cases across the US is part of the same outbreak. No common events such as social gatherings can be linked to all the patients.

Iowa has reported 138 cases of cyclospora, followed by Texas (71), Nebraska (70), Florida (23) and New York City (4). Other states have reported three or fewer cases.

It typically takes about one week between being infected with cyclospora and the first signs of symptoms. The parasite infects the small intestine and "usually causes watery diarrhea, with frequent, sometimes explosive, bowel movements," according to the FDA.

Cyclospora infection is not thought to be life-threatening, though a spokesperson for the Nebraska Department of Health and Human Services said some infected residents dropped 25 pounds while fighting the illness.

Other symptoms include loss of appetite, weight loss, stomach cramping or bloating, flatulence, fatigue, and in some cases vomiting, headache, fever and other flu-like symptoms are observed. It is typical for the infected to observe their symptoms going away and later relapsing. Some people infected with the parasite do not show any symptoms.

If untreated, a cyclospora infection can last as long as 57 days, according to Ann Garvey, deputy state epidemiologist for the Iowa Department of Public Health.

Public health officials in Iowa and Nebraska suspect the outbreak in the states was a vegetable that was shipped into their territory, rather than a local product, according to the Wall Street Journal.

The FDA and CDC have both reported that they will make more information about the cyclospora outbreak public as it becomes available.