Why the "explosive" stomach bug outbreak remains a mystery

• "Nobody's identified a source yet ... or a particular food or a particular line of transmission, but there's something going on," David Freedman, MD, a professor emeritus of infectious diseases at the University of Alabama at Birmingham, told Axios.

Catch up quick: The Centers for Disease Control and Prevention has identified at least 843 confirmed domestic cases of the disease and over 1,500 cases that require further analysis before they can be confirmed as cyclosporiasis.

• The data is current up to July 9. The CDC had only reported 145 cases as of mid-June.
• "There is currently no evidence of a single, multi-state cyclospora outbreak linking all cases," the CDC says. "Investigations to identify potential sources are ongoing."

Yes, but: Multiple states — like Michigan, Ohio and New York — are reporting higher numbers for the disease, which can cause people to have "explosive" or "watery" diarrhea.

• "Right now it's individual state health departments that are having to speak up because the CDC is really not following it on a day-to-day basis," Freedman tells Axios.
• States are required to report case numbers monthly, which can account for differences between their numbers and those from the CDC, a spokesperson from the Department of Health and Human Services told Axios.
• "In response to increasing case counts in some states, CDC is now requesting weekly case count updates," the HHS spokesperson said.

Mystery remains over parasitic illness

The latest: Michigan has become the epicenter of the outbreak, with more than 1,500 cases and no identifiable source, officials said Friday.

• Less than a week ago, the state reported around 680 cases.

What they're saying: "There's clearly something unusual going on out of Michigan," Freedman says. "It's probably something local or regional that people are eating."

Between the lines: The CDC says it stopped requiring tracking as of July 1 for everything except Salmonella and shiga-producing E. coli — meaning tracking for cyclosporiasis is now done only by state or local agencies.

How cyclosporiasis spreads

Cyclosporiasis doesn't spread person-to-person, but rather as people eat food contaminated by the Cyclospora cayetanensis parasite.

• "It's not like COVID, it's not like the flu," Freedman says, adding that people in the same household get sick from eating "the same batch of berries that was bought at the supermarket."
• He says it's possible cases have spread beyond Michigan because people traveled through the state over the summer, and that another state — like Ohio — could be the actual epicenter.

Zoom in: Steven Goldberg, chief medical officer at HealthTrack and an urgent care physician, tells Axios that by the time someone realizes they're sick, the contaminated food is likely already in the trash or has been consumed.

• "People also have difficulty recalling exactly which produce items they consumed a week or more earlier," Goldberg says.

What to watch for: Symptoms usually appear about a week after consuming contaminated food or drink, according to the CDC.

• Though rarely life-threatening, the sickness can trigger "explosive" or "watery" diarrhea lasting days or even more than a month without treatment.

Threat level: "Most cases of food poisoning ... make you miserable for a few days and then resolve on their own," but the parasite cyclospora "plays a much longer game."

• The bug doesn't "'run its course' the way a stomach bug typically does," Goldberg says, adding: "This is not a 'wait it out' illness."
• Rather, the disease requires a prescription for trimethoprim-sulfamethoxazole, an antibiotic used to treat bacterial infections.