Cyclospora Outbreak Sickens Over 2,900 People Across 31 States

The illness, cyclosporiasis, causes prolonged diarrhea that can last up to a month if untreated. The parasite is typically spread through raw produce such as lettuce, basil, cilantro, and raspberries that has been exposed to human waste in warm conditions.

Michigan has recorded more than 1,500 cases during this outbreak, compared with its usual annual total of about 50. Most other states reporting cases have recorded fewer than 10 each, numbers that fall within normal summer ranges. The CDC updated its national case count from fewer than 200 to 843 after state reports showed higher totals. A CDC spokesperson did not explain the earlier discrepancy.

Public-health officials have not determined whether the cases are linked or identified a common source. One theory from a Rutgers University food scientist points to possible water exposure such as Lake Erie. Michigan's chief medical executive has stated the state is investigating a produce link.

Washing produce may reduce but does not eliminate risk, because the number of parasites needed to cause infection is not known. Thorough cooking kills the parasite.

Genetic sequencing used to link other foodborne outbreaks is less effective for Cyclospora because the parasite is difficult to extract from stool samples and cannot be grown in laboratories. Past investigations have identified suspected sources without establishing how contamination occurred.

The investigation has been underway for nearly a month. Nearly 100 people have been hospitalized so far, with no deaths reported.