When we think of foodborne illness outbreaks in restaurants, bacteria like Salmonella or E. coli usually come to mind. But another category of pathogens is often overlooked and just as dangerous: parasites. Though less common than bacterial outbreaks, parasitic infections can cause severe illness, prolonged symptoms, and even long-term health complications. In restaurant settings, where food handling, hygiene, and ingredient sourcing are critical, parasitic outbreaks pose a real threat to public health.
Here’s a closer look at the most common parasites responsible for restaurant-related outbreaks, how they spread, and what restaurants and diners can do to stay safe.
1. Giardia lamblia
What it is: Giardia is a microscopic protozoan parasite that infects the small intestine and causes giardiasis, one of the most commonly reported parasitic illnesses in the U.S.
How it spreads in restaurants:
- Infected food handlers who don’t wash hands properly
- Fresh produce washed with contaminated water
- Ice or water served to customers without proper filtration
Symptoms: Watery diarrhea, abdominal cramps, bloating, fatigue, and weight loss. Symptoms can last for several weeks and often return if not properly treated.
Real-world examples: Outbreaks have occurred in restaurants where food workers were infected or improper sanitation practices allowed the parasite to spread. In July 2025, a Giardia outbreak at El Tapatio restaurant in Kentucky sickened at least two dozen people and led to a lawsuit.
2. Cyclospora cayetanensis
What it is: Cyclospora is another protozoan parasite that causes cyclosporiasis, a gastrointestinal illness that has been increasingly linked to imported fresh produce.
How it spreads in restaurants:
- Contaminated herbs like cilantro, basil, or parsley
- Berries and leafy greens washed or irrigated with dirty water
- No person-to-person transmission, but handling contaminated ingredients can infect diners
Symptoms: Profuse diarrhea, nausea, loss of appetite, gas, and fatigue. The illness can last for weeks or relapse without antibiotic treatment.
Real-world examples: In the last decade, the U.S. has seen multiple large outbreaks of Cyclospora linked to restaurants and foodservice settings. In 2018, more than 500 people were sickened after eating salads served at a fast food chain that sourced contaminated produce.
3. Toxoplasma gondii
What it is: Toxoplasma is a parasitic protozoan that causes toxoplasmosis, a usually mild illness in healthy individuals but potentially serious in pregnant people or those with weakened immune systems.
How it spreads in restaurants:
- Undercooked or raw meat (especially pork and lamb)
- Cross-contamination from contaminated surfaces
- Occasionally through unwashed produce
Symptoms: Mild flu-like symptoms in most people, but it can lead to miscarriage, birth defects, or neurological issues in high-risk individuals.
Real-world examples: While outbreaks are less common than individual cases, improper cooking of meat in restaurants can lead to isolated cases of toxoplasmosis. The CDC estimates that Toxoplasma is one of the leading causes of death from foodborne illness in the U.S.
4. Anisakis and Other Fish-Borne Parasites
What it is: Anisakis is a roundworm parasite found in raw or undercooked seafood, particularly fish like salmon, cod, and herring.
How it spreads in restaurants:
- Serving raw fish (e.g., sushi, ceviche) that hasn’t been properly frozen to kill parasites
- Inadequate training in handling sushi-grade fish
Symptoms: Abdominal pain, nausea, vomiting, and in rare cases, allergic reactions. The parasite can embed in the stomach or intestinal wall, requiring endoscopic removal.
Real-world examples: While rare in the U.S. due to regulations requiring freezing of raw fish, cases do still occur, especially in restaurants not following strict guidelines for sushi preparation.
5. Trichinella spiralis
What it is: This parasite causes trichinosis, a disease historically associated with undercooked pork. Thanks to better farming and inspection practices, it’s now rare in the U.S.
How it spreads in restaurants:
- Serving undercooked pork or wild game meat
- Lack of awareness of internal cooking temperature requirements
Symptoms: Nausea, diarrhea, followed by muscle pain, swelling, and fever as the larvae migrate to muscle tissue. In severe cases, it can be life-threatening.
Real-world examples: Occasional outbreaks still occur, usually in restaurants serving wild boar or other game meats without proper temperature controls.
Prevention: What Restaurants Can Do
To prevent parasitic outbreaks, restaurants must take hygiene and sourcing seriously:
- Thorough handwashing protocols for staff
- Proper cooking temperatures for all meat and fish
- Use of filtered or treated water for washing produce and making ice
- Sourcing produce from certified, reputable suppliers, especially when imported
- Staff education on symptoms of parasitic infections and exclusion from work if ill
What Diners Should Know
Although diners can’t control what happens in the kitchen, they can reduce risk by:
- Avoiding raw or undercooked meat and fish, especially in unfamiliar restaurants
- Asking questions about how produce is washed or where fish is sourced
- Notifying local health departments if they become sick after dining out
Final Note
Parasitic outbreaks in restaurants may be less frequent than bacterial ones, but they often involve longer-lasting and harder-to-diagnose illnesses. They also underscore the importance of global food safety, since many outbreaks are linked to imported produce or improperly handled meat and seafood.
With growing interest in raw and minimally processed foods, the restaurant industry must remain vigilant. For customers and restaurants alike, awareness and prevention are the best defenses against these hidden threats.
