U.S. Cyclospora Case Surge: Symptoms, Testing, and When to Get Care

ByBrian “Weence” Bateman

CDC says cyclosporiasis cases have increased in the U.S. Prolonged watery diarrhea can last weeks, and routine stool testing may miss Cyclospora. Here’s what to ask about Cyclospora-specific testing, what results can mean, and what CDC says about treatment with TMP-SMX and key safety cautions.

CDC is reporting a summertime increase in cyclosporiasis (caused by the microscopic parasite Cyclospora). If you or someone in your family has prolonged watery diarrhea, it’s worth asking whether Cyclospora testing should be considered.

Current U.S. situation: CDC surveillance notes 843 confirmed domestic cases as of July 9, 2026 (since May 1, 2026), including 86 hospitalizations and 0 reported deaths. CDC also cautions that case counts can be affected by a reporting lag and that the “true number” may be higher because some people recover without medical care and aren’t tested.

Symptoms families may notice

Cyclosporiasis can cause an intestinal illness that often includes:

  • Watery diarrhea
  • Loss of appetite
  • Weight loss

CDC notes that if untreated, illness may last a few days to a month or longer. Symptoms may also seem to go away and then return (relapse).

Testing reality check: why routine stool tests can miss Cyclospora

Even when someone has symptoms, diagnosis can be tricky. CDC says Cyclospora testing is not routinely conducted in most U.S. laboratories, even when stool is tested for parasites. CDC also notes that not all gastrointestinal PCR panels include a target for Cyclospora.

CDC further explains why results can be negative despite symptoms:

  • Oocysts may be hard to detect because symptomatic patients might not shed enough to be readily detectable.
  • Shedding can be intermittent, so patients might need to submit several specimens on different days.
  • Labs may need sensitive recovery methods (concentration) and detection methods that highlight Cyclospora oocysts.

CDC lists lab approaches such as modified acid-fast staining and modified (“hot”) safranin, plus UV fluorescence microscopy (because Cyclospora oocysts autofluoresce). ASM’s lab-focused guidance adds that routine O&P exams generally will not readily detect Cyclospora, and it recommends UV microscopy when possible.

The “what to ask” checklist for clinicians and labs

If diarrhea has been ongoing and Cyclospora is on the table, consider asking:

  • “Can we specifically request Cyclospora testing?” (CDC says providers should request testing when indicated.)
  • “Does your lab use Cyclospora-appropriate methods?” Ask whether the lab can do approaches like modified acid-fast, modified (“hot”) safranin, and/or UV fluorescence microscopy, and whether it can use concentration procedures.
  • “If the first test is negative, do I need more specimens?” CDC notes patients might need several stool samples collected on different days.
  • “Does the routine O&P test include Cyclospora detection?” ASM advises clinicians/labs that routine O&P will not readily detect Cyclospora.
  • “Does your PCR panel include Cyclospora?” CDC notes not all panels include it.
  • “How will confirmed cases be handled for reporting?” CDC surveillance guidance emphasizes that confirmed cases should be reported to local health departments.

If results are negative but symptoms persist

A negative stool test does not always mean Cyclospora isn’t the cause. CDC explains that even symptomatic people may not shed enough oocysts for easy detection, and patients may need additional specimens collected on different days using recovery and detection methods that highlight Cyclospora.

If you’re still having significant symptoms after an initial test, follow up promptly and ask whether further Cyclospora-appropriate testing (and/or repeat specimens) is reasonable.

Treatment overview (CDC): TMP-SMX, plus key safety cautions

CDC lists TMP-SMX (trimethoprim-sulfamethoxazole) as the treatment of choice for cyclosporiasis. CDC also notes that many healthy people eventually recover even without treatment, though illness may be prolonged.

Typical CDC dosing guidance (summarized):

  • Adults: TMP 160 mg + SMX 800 mg (one double-strength tablet) by mouth twice daily for 7–10 days.
  • People with HIV: may need longer courses.
  • Children (≥2 months to 18 years): weight-based dosing for 7–10 days.

Important safety considerations CDC highlights:

  • Pregnancy: TMP-SMX is a pregnancy category C drug; CDC advises use only if benefit justifies risk, and it should be avoided near-term due to potential risk of hyperbilirubinemia and kernicterus in the newborn.
  • Lactation: TMP-SMX is excreted in breast milk and is generally compatible for healthy, full-term infants after the newborn period, but CDC says it should be avoided if nursing infants are premature, jaundiced, ill or stressed, or have G6PD deficiency.
  • Young infants: CDC says safety in children under 2 months has not been systematically evaluated, and use generally is not recommended.

What to do next (practical steps while investigations continue)

  • Get medical care if diarrhea is persistent or causing concern. If someone can’t keep fluids down or shows signs of dehydration, seek urgent or emergency care.
  • Tell your clinician about how long symptoms have lasted and share relevant exposure details (such as recent travel or food/water exposures).
  • Ask about the testing plan: how many specimens are needed, whether Cyclospora-specific methods will be used, and whether repeat specimens are needed if the first result is negative.
  • If Cyclospora is confirmed, ask your clinician how reporting to local public health authorities is handled.

What’s still uncertain: public health investigations are working to identify clusters and possible sources, and CDC case counts can rise as additional data are confirmed and reported.

Sources

Editorial note: Weence articles are researched from cited public-health, medical, regulatory, journal, and reputable news sources and may be drafted with AI assistance. They are checked for source support, clarity, and safety guardrails before publication.

This article is for general informational purposes only and is not medical advice. Research findings can be early or incomplete, and health guidance can change. Always talk with a qualified healthcare professional about personal symptoms, diagnosis, medications, vaccines, screenings, or treatment decisions. If you think you may have a medical emergency, call emergency services right away.

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Brian “Weence” Bateman is a health and medical writer who covers public health updates, healthcare policy, and medical developments affecting communities across the United States. He works closely with dentists and healthcare providers and focuses on making complex medical information clear, accurate, and useful for everyday readers.