Health officials are warning that what many people dismiss as a routine summer stomach bug may actually be cyclosporiasis, as the U.S. experiences one of its largest foodborne parasite outbreaks on record.

The Centers for Disease Control and Prevention has confirmed more than 1,600 domestic cases of cyclosporiasis since May, with over 5,100 additional cases currently under investigation.

The intestinal infection is caused by Cyclospora (Cyclospora cayetanensis), a microscopic parasite that spreads through contaminated food or water.

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The outbreak has sickened thousands of people, particularly in Midwestern states such as Michigan and Ohio, causing prolonged bouts of severe gastrointestinal illness.

Symptoms usually begin about one week after consuming contaminated food or water, although the incubation period can range from about two days to two weeks, according to the CDC.

Early symptoms can overlap with those of a common viral stomach bug, including abdominal pain, nausea and watery diarrhea. Some patients also experience loss of appetite, fatigue and weight loss.

The primary differences lie in how long the illness lasts and how severe the symptoms become, according to Dr. Kenneth Perry, an emergency physician based in South Carolina.

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Routine stomach bugs are typically short-lived, resolving within 24 to 48 hours, the doctor said. Even if mild symptoms linger, patients generally feel better after two days.

“Cyclospora is different in this regard,” Perry told Fox News Digital. “It lasts longer, with far more profound watery, foul-smelling diarrhea and abdominal cramping.”

A massive surge in Cyclospora cases means people may be mistaking this parasitic foodborne infection for a standard summer stomach bug. (iStock)

It is possible to test for Cyclospora, but healthcare providers must specifically request it, as the parasite is not routinely included in standard stool testing and many gastrointestinal PCR panels do not detect it, according to the CDC.

Diagnosis is made by examining stool specimens, although patients may need to submit several samples collected on different days, as even symptomatic people may not shed enough of the parasite for it to be readily detected, per the above source.

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If symptoms strongly suggest Cyclospora despite an initial negative test, the screening may need to be repeated, Perry noted.

A primary care physician is often the best point of contact for patients seeking a diagnosis, as most routine stool tests performed in emergency departments do not screen for Cyclospora. A family doctor can order the specialized test if it’s suspected.

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“The emergency department is the appropriate setting for treating downstream symptoms, such as nausea, diarrhea and dehydration,” Perry told Fox News Digital.

People who suspect they have contracted the parasite can also check FDA and CDC food safety alerts to see whether they may have been exposed to a recalled or implicated product.

While routine stomach viruses usually resolve within 48 hours, Cyclospora infections linger much longer with severe, watery and foul-smelling diarrhea. (iStock)

Patients should also focus on staying hydrated by monitoring their urine output. Perry recommends using over-the-counter pediatric formulas, which offer a more effective salt-to-sugar ratio than commercial sports drinks.

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Anyone whose diarrhea lasts more than two to three days, worsens or is accompanied by signs of dehydration should contact a primary care physician.

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Unlike most viral stomach bugs, Cyclospora is treatable with prescription antibiotics. The CDC recommends trimethoprim-sulfamethoxazole (TMP-SMX) as the standard treatment, while people who cannot take sulfa drugs should discuss alternatives with their healthcare provider.