(NEXSTAR) – More cases have been linked to outbreaks of cyclospora that do not have an identified source, according to the Food and Drug Administration. The outbreak linked to iceberg lettuce, meanwhile, has expanded to two additional states.

There have been nearly 14,000 cases of domestically acquired cyclospora confirmed in the U.S. since May this year, the Centers for Disease Control and Prevention report. That's well over the roughly 1,180 cases reported from May through August last year.

Of this year's cases, at least 9,480 were reported in the 17 states connected to the cyclospora outbreak traced back to iceberg lettuce, according to the FDA and the CDC. Two states, Maine and Massachusetts, were added to that tally late last week.

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At least some of the nation's cases are also linked to the ongoing cyclospora outbreaks that the FDA has been investigating.

There are seven active investigations into cyclospora outbreaks, the FDA's tracking shows. Three – sickening 18, eight and two people, respectively – are listed as ended. Only the outbreak linked to iceberg lettuce has an identified source.

Two outbreaks have grown, according to the FDA. One, which was first reported in early August, has grown to 11 cases. Another, from late July, has grown to 172 cases, up from 115. The FDA continues to conduct traceback in both outbreaks, as well as three other still active outbreaks.

We may never know the cause of the outbreak. Because of how long it can take for people to experience symptoms, and the difficulties of sequencing cyclospora, investigations can "take a significant amount of time," Gwen Biggerstaff, the deputy director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, previously explained.

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It's also likely that the true number of people who have fallen ill this summer is higher than the tallies the CDC and state officials are reporting. Not everyone who becomes infected experiences symptoms, requires hospitalization or undergoes testing to confirm their diagnosis. Symptoms can also take weeks to set in.

A Nexstar analysis of health data across several states shows more than 30,000 cases of cyclosporiasis have been confirmed or reported as probable across the U.S. this year. These cases included those that have been acquired domestically and internationally, and, in some states, tests that have not yet been laboratory confirmed.

Two patients in Michigan died after becoming ill prior to the lettuce recall, though state health officials warned that "both individuals had significant underlying health conditions."

Healthcare experts encourage those experiencing symptoms, especially diarrhea that lasts more than a week or two, to seek medical care.

Left untreated, cyclosporiasis can stick around for a month or longer. Treatment can include antibiotics, antidiarrheal medications and hydration, according to the Cleveland Clinic.

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