Parasite season, specifically Cyclospora season, is showing no signs of ending early this year, with the CDC reporting more than 1,600 people infected since May 1.

The laboratory-confirmed patients span 33 states and the District of Columbia, according to an updat posted late Thursday by the Centers for Disease Control and Prevention. The report specifically delineates between “domestically acquired” cases of cyclosporiasis among people in the United States and infections in people who traveled internationally during the 14 days before becoming sick.  

Of patients for whom the complete information is available, 92 have been so sick they had to be admitted to hospitals. The CDC reported the number of cases increased from the previous month and “remains elevated in the United States since May 1.”

“While cyclosporiasis cases are reported year-round in the United States, cyclosporiasis acquired in the United States. . . is most common during the spring and summer months,” according to the CDC report. “The exact timing and duration of U.S. cyclosporiasis seasons can vary, but reports tend to increase starting in May. 

In previous years the reported number of cases peaked between June and July, although activity can last as late as September, according to the CDC.

“At this time, multiple clusters of cases associated with different restaurants or events are being investigated by state public health authorities, CDC, and FDA,” the CDC reported.

Some of the outbreak patients this year are associated with a cluster of illnesses linked to consumption of fresh basil imported from Siga Logistics de RL de CV of Morelos, Mexico. Federal officials continue to investigate that multistate outbreak. They are also working to determine common denominators among other infected people.

Many cases of cyclosporiasis could not be directly linked to an outbreak, in part because of the lack of validated molecular typing tools for C. cayetanensis according to the CDC update.

The CDC’s Thursday night updat also reported the median illness onset date of June 29, with an overall range of May 1 through Aug. 13.