Cyclosporiasis outbreak: why the CDC investigation now reportedly spans 15 states

The US Centers for Disease Control and Prevention has reportedly expanded its investigation into the largest known cyclosporiasis outbreak to 15 states, according to a Washington Post report citing three people familiar with the matter.

Cyclosporiasis is an intestinal illness caused by a microscopic parasite, Cyclospora cayetanensis, typically spread through fresh produce or water contaminated with feces. Its hallmark symptom is watery diarrhea that can last for weeks, sometimes accompanied by cramping, bloating, fatigue and a low-grade fever. Treatment usually involves the antibiotic combination trimethoprim-sulfamethoxazole.

According to the Washington Post report, which cited three people familiar with the matter, six additional states were added to the investigation: Arkansas, Iowa, Missouri, Nebraska, New Hampshire and North Carolina, according to a fourth person familiar with the matter, bringing the total to 15 states.

The expansion followed Michigan's health department reporting the first two US deaths linked to the outbreak, marking the first fatalities recorded in the investigation.

State officials said medical records showed both individuals had significant underlying health conditions that may have been impacted by cyclosporiasis and dehydration, underscoring that the illness rarely proves fatal in otherwise healthy people, even though it can cause prolonged and debilitating symptoms, particularly in people who are immunocompromised, elderly or already vulnerable gastrointestinally.

Epidemiologists typically trace outbreaks like this through case-control interviews, genetic fingerprinting of samples and supply-chain tracing to identify a common food source. In recent years, US cyclosporiasis outbreaks have repeatedly been linked to imported fresh herbs and leafy produce, such as cilantro and basil, though pinpointing the exact source of any single outbreak can take weeks.

The outbreak's description as the largest known cyclosporiasis outbreak in the US points to a significant scale, though initial reporting has not specified an exact case count. Investigations of this kind typically expand geographically, as CDC's usual practice, as more state health departments identify matching cases through laboratory testing.

Cyclosporiasis cases in the US typically climb during the summer months, tied to fresh produce consumption and import patterns, and public health agencies routinely see multi-state outbreaks during this period of the year.

The CDC and food safety experts generally recommend washing fresh produce thoroughly, exercising caution with pre-cut fruit or herbs of unclear origin, and seeking medical care for watery diarrhea that persists for more than a few days, since the illness responds to a specific antibiotic treatment unlike most viral gastroenteritis.

As the investigation continues, health officials say identifying a specific food source will be central to curbing further cases across the states now covered by the inquiry.