CDC Investigates Seasonal Increase in Cyclospora Infections Across the United States
US public health officials are investigating a sharp seasonal increase in cyclosporiasis, a parasitic infection that can cause severe watery diarrhea. Hundreds of laboratory-confirmed cases have been reported in recent weeks as summer travel and outdoor gatherings increase across the country, although investigators have not yet identified the source of the rise.
Cyclosporiasis is caused by the parasite Cyclospora cayetanensis. People become infected after consuming food or water contaminated with feces containing the parasite. While officials believe contaminated food or water within the United States is responsible for many recent cases, the exact source remains unknown.
Most Recent Cases Were Acquired Within the United States
According to the US Centers for Disease Control and Prevention (CDC), 190 laboratory-confirmed cases of cyclosporiasis were reported between early May and mid-June. Among them, 145 patients had not traveled outside the United States during the two weeks before becoming ill.
Because the parasite is not spread directly from one person to another, these domestically acquired infections suggest exposure to contaminated food or water within the country. However, the CDC says there is currently no evidence linking all of the reported illnesses to a single multistate outbreak.
Cases have been identified in at least 17 states. New York has reported the highest number of infections, while additional cases have been confirmed in states including Texas, Colorado, and Alaska, indicating that several localized contamination events may be occurring.
Most Patients Recover, but Some Require Hospital Care
Among the 145 domestically acquired cases for which complete information was available, patients ranged in age from 5 to 86 years, with a median age of 42. Approximately 61% were female, and at least 20 people required hospitalization. No deaths have been reported.
An additional 45 infections were associated with international travel. These patients ranged in age from 17 to 89 years, with a median age of 43. Three people in this group were hospitalized, and no deaths were recorded.
Health officials believe the true number of infections is likely higher than reported because many people with mild or moderate illness may not seek medical care or undergo laboratory testing.
Symptoms Can Persist for Weeks Without Treatment
Cyclosporiasis most commonly causes frequent watery diarrhea that can be severe and prolonged. Other symptoms include abdominal cramps, bloating, nausea, loss of appetite, weight loss, and marked fatigue. Illness usually begins about one week after exposure to the parasite.
Some people also experience vomiting, headaches, muscle aches, and a low-grade fever. Without appropriate treatment, symptoms may continue for several weeks or recur over the course of a month or longer.
The recommended treatment is an antibiotic combination of trimethoprim and sulfamethoxazole. Although some infections resolve without medication, healthcare providers note that diagnosis is important because routine stool tests do not always include screening for Cyclospora unless it is specifically requested.
Investigators Continue to Search for the Source
The CDC, the US Food and Drug Administration (FDA), and state and local health departments are investigating several clusters of illness reported across multiple states. Investigators are interviewing patients about the foods and beverages they consumed before becoming sick in an effort to identify shared sources of exposure.
Previous outbreaks in the United States have frequently been linked to fresh produce that is difficult to disinfect completely, including cilantro, basil, berries, and leafy greens. One multistate outbreak in 2018 was traced to salads sold at McDonald's restaurants.
At this stage, officials have not identified any specific food item responsible for the current increase in infections. Healthcare providers are being encouraged to consider cyclosporiasis in patients who develop persistent diarrhea during the summer months.
Why Cases Increase During the Summer
Cyclosporiasis is a nationally notifiable disease in many US states, and health authorities closely monitor cases between May and August, when infections typically become more common. Seasonal increases are thought to be related to greater consumption of fresh produce, outdoor dining, and warmer weather.
The parasite is most frequently found in parts of Central and South America, South and Southeast Asia, the Middle East, and Africa. Travelers visiting these regions may become infected through contaminated food or untreated drinking water.
Unlike many intestinal infections, Cyclospora cannot spread directly from one infected person to another. The parasite must first mature in the environment before it becomes capable of causing infection, making it more difficult for investigators to identify the exact source of contamination.
How to Reduce the Risk of Infection
Health experts recommend washing hands thoroughly with soap and water before eating and after using the bathroom. Travelers to higher-risk regions are advised to drink bottled water, avoid ice made from uncertain water sources, and choose sealed, pasteurized beverages whenever possible.
Fresh fruits and vegetables should be washed carefully under running water before consumption, although washing alone may not completely eliminate the parasite. Proper cooking also helps destroy many foodborne pathogens, including parasites.
Anyone who develops diarrhea lasting more than a few days, or symptoms that improve before returning, should seek medical advice. Health officials also encourage patients to remember what they ate during the week before becoming ill, as this information can help investigators trace the source of infection.
Health Officials Expect Ongoing Monitoring
More than 1,000 confirmed cases of cyclosporiasis were reported in the United States last year, and researchers say similar or higher numbers could occur this year. Factors such as global food distribution and changing environmental conditions may also influence the spread of foodborne parasites.
For now, public health officials remain focused on identifying contaminated products and issuing warnings if necessary. Although cyclosporiasis can cause prolonged illness, early diagnosis and appropriate antibiotic treatment are effective for most patients.
The CDC is expected to continue updating case numbers and investigation findings throughout the summer as efforts to identify the source of the current increase continue.
