This summer the United States has been dealing with its largest Cyclospora outbreak ever recorded — and because the illness it causes can drag on for weeks and mimics ordinary "stomach bugs," many people are sick right now without knowing what they have. Here is a complete guide from our clinical team: what happened, how to recognize the illness, how we test for it at our Pasadena clinic, and how it is treated.
What happened
Since May 1, 2026, the CDC has reported more than 17,000 laboratory-confirmed cases of cyclosporiasis acquired in the United States, with thousands of additional suspect cases still under review. For perspective, the same window last year produced about 1,200 cases — this year is roughly fifteen times larger, prompting a CDC Health Advisory to clinicians nationwide.
The largest identified cluster — more than 11,000 cases across 20 states — has been linked by CDC and FDA investigators to processed iceberg lettuce distributed to restaurants and food service. At least six additional clusters remain under investigation with no confirmed source yet. Because implicated produce moves through national supply chains and case reporting lags by weeks, cases have appeared far beyond the states first involved — which is why we are talking about it with patients here in Pasadena.
What is Cyclospora?
Cyclospora cayetanensis is a microscopic, single-celled parasite spread when food or water is contaminated — classically imported fresh produce such as leafy greens, basil, cilantro, and berries. It is not spread person-to-person the way norovirus is: the parasite needs days-to-weeks outside the body to become infectious, so catching it directly from a sick family member is essentially unheard of. One more uncomfortable fact: Cyclospora clings to produce and survives routine washing better than most germs, so while rinsing produce is always good practice, it cannot reliably remove this particular parasite — avoiding implicated products is what works.
Symptoms: how it differs from an ordinary stomach bug
Symptoms typically begin about one week after exposure (range 2–14 days), which means people rarely connect the illness to the meal that caused it. The hallmark picture:
- Frequent, watery diarrhea — sometimes explosive, often worse in the morning
- Loss of appetite and weight loss
- Cramping, bloating, and increased gas
- Profound fatigue — often out of proportion to the GI symptoms
- Nausea (vomiting is less common), and sometimes a low-grade fever
Two features should make you think Cyclospora rather than a routine viral bug: duration and relapse. Untreated, the illness commonly lasts two to six weeks or longer, and it is famous for seeming to improve and then coming back in waves. A "stomach flu" that is still going — or keeps returning — after a week is not behaving like a virus and deserves testing.
Testing: why the standard workup can miss it
Cyclospora is a classic example of "you only find it if you look for it." Routine stool cultures do not detect parasites, and even a standard ova-and-parasites exam can miss it unless the lab uses the right techniques. The two reliable approaches:
- Molecular GI pathogen panels (PCR) — a single stool sample tested against a panel of bacteria, viruses, and parasites including Cyclospora. This is the fastest and most sensitive option and has become the workhorse during this outbreak.
- Targeted microscopy — an ova-and-parasites examination using a modified acid-fast stain (or UV fluorescence microscopy), which makes the oocysts visible; the lab must specifically be asked to look for Cyclospora.
At Advanced Urgent Care of Pasadena, we can collect the sample during your visit through our on-site laboratory, order the appropriate testing, and reach you promptly with results — no appointment needed, seven days a week.
Treatment: what actually works
1. The antibiotic of choice: trimethoprim-sulfamethoxazole (Bactrim). Unlike most causes of diarrhea, cyclosporiasis has a specific, effective treatment — a course of Bactrim typically shortens the illness dramatically and prevents the relapsing pattern. This is the single biggest reason to get tested rather than wait it out: without treatment the illness can smolder for a month or more; with the right antibiotic most people improve within days. If you are allergic to sulfa drugs, tell the provider — alternatives are limited and that conversation matters.
2. Hydration, hydration, hydration. Weeks of watery diarrhea quietly drains the body of fluid and electrolytes. Water alone is not ideal — oral rehydration solutions or electrolyte drinks replace what is actually being lost. Warning signs of dehydration — dizziness on standing, dark or scant urine, dry mouth, a child crying without tears — mean it is time to be seen; when needed, we can assess hydration and escalate care the same day.
3. Let your gut rest with gentle eating — the BRAT approach. While recovering, bland, binding, low-fat foods are easiest to tolerate: Bananas, Rice, Applesauce, and Toast, plus similar gentle options like crackers, plain potatoes, and broth. Use it as a short-term bridge for a day or two while symptoms are at their worst, then expand back to a normal balanced diet as tolerated — prolonged restrictive eating slows recovery. Skip alcohol, caffeine, dairy, and greasy or spicy food until your gut settles.
When it’s the ER instead
Go to the emergency room or call 911 for signs of severe dehydration (confusion, fainting, no urination), bloody stool, severe or localized abdominal pain, high fever with rigors, or any GI illness in someone frail, immunocompromised, or pregnant who is deteriorating. For everything short of that, urgent care is the right first stop — our ER vs. urgent care guide covers the line in detail.
The bottom line for Pasadena families
- A diarrheal illness that lasts beyond a week or keeps relapsing — especially after eating salads or fresh produce — deserves testing for Cyclospora, particularly during this record outbreak.
- Testing is a simple stool sample; treatment (Bactrim) is effective; supportive care is hydration and gentle eating.
- And year-round, remember norovirus — the endemic fast-moving vomiting bug — behaves differently: sudden onset, 1–3 days, no antibiotics; hydration is the treatment and handwashing with soap (not just sanitizer) is the prevention.
Walk in any day — Monday–Friday 8 AM–8 PM, weekends 9 AM–5 PM (we take our last patient 30 minutes prior to close) — at 797 S Arroyo Pkwy, Pasadena, with free parking. Questions? Call (626) 304-0404.
Sources: CDC Health Advisory on domestically acquired cyclosporiasis (2026); CDC/FDA multistate outbreak investigation of Cyclospora infections linked to iceberg lettuce; CDC cyclosporiasis surveillance data, May–August 2026.