US cyclospora outbreak: Why a treatable infection has turned deadly

Thousands of infections, two reported deaths, and a growing investigation. Here's why the ongoing cyclospora outbreak in the US is drawing attention

  The largest recorded cyclospora outbreak in the United States has taken a worrying turn after Michigan reported the country's first deaths linked to the parasitic infection. While cyclosporiasis is generally considered treatable and rarely fatal, the outbreak has already sickened thousands of people across multiple states and prompted recalls of fresh produce as investigators continue searching for the exact source.

 

What is cyclosporiasis?

 

According to the US Centers for Disease Control and Prevention (CDC), cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. People can become infected after consuming food or water contaminated with the parasite, although the illness is not usually life-threatening.

 

The CDC says Cyclospora spreads when people eat food or drink water contaminated with faeces. However, it does not usually spread directly from one person to another because the parasite needs at least one to two weeks outside the human body to become infectious. As a result, contaminated fresh produce and water are the most common sources of infection.

 

Why is this outbreak different?

 

Cyclospora outbreaks occur almost every year in the US, particularly during the warmer months, but this year's outbreak is unprecedented in both its scale and severity.

 

According to the CDC, more than 18,000 domestic cyclosporiasis cases have been identified this season, including 6,707 laboratory-confirmed infections. Another 11,500 suspected cases are still undergoing laboratory testing and analysis, making it the largest recorded Cyclospora outbreak in the US.

 

The agency has identified nine states linked to the ongoing outbreak: Illinois, Indiana, Kansas, Kentucky, Michigan, Ohio, Oklahoma, Pennsylvania, and West Virginia. Among them, Michigan has reported the highest number of cases, with 11,234 infections, including 193 hospitalisations. The state has also reported the first two deaths linked to the ongoing outbreak.

 

Investigators have linked many cases to shredded iceberg lettuce served at Taco Bell restaurants. Taylor Farms recalled iceberg lettuce grown in central Mexico after it was identified as a potential source. However, officials continue to investigate because some infections may be linked to other fresh produce, including herbs such as parsley or cilantro.

 

What are the symptoms?

 

According to the CDC, symptoms usually appear about a week after infection and can last for several weeks if left untreated.

 

Common symptoms include:

 

• Watery diarrhoea
• Loss of appetite
• Weight loss
• Stomach cramps
• Bloating
• Nausea
• Fatigue
• Low-grade fever

 

The agency says some people experience symptoms that improve before returning. Severe diarrhoea can also lead to dehydration, particularly in older adults and people with weakened immune systems.

 

Who is most at risk?

 

Most healthy people recover completely, especially with prompt treatment. However, the risk of severe illness is higher among:

 

• Older adults
• Young children
• People with weakened immune systems
• Those with serious underlying health conditions

 

The Michigan Department of Health and Human Services said both people who died in Michigan had pre-existing medical conditions that were likely worsened by the infection and dehydration rather than by the parasite alone.

 

Why is Cyclospora difficult to trace?

 

One of the biggest challenges in controlling a Cyclospora outbreak is identifying its source. Unlike bacteria, there is no routine whole-genome sequencing available to "fingerprint" the parasite and link infections to a specific food source.

 

Scott Gottlieb, former commissioner of the U.S. Food and Drug Administration, told Reuters: “FDA relies on whole genome sequencing to effectively fingerprint a pathogen, to try to isolate a particular pathogen to a particular outbreak to a particular grower. You don’t have that in this case.”

 

The parasite is also difficult to detect in food samples, as contaminated produce is often eaten or discarded before investigators can test it. Moreover, fresh vegetables move through complex supply chains, making it harder to pinpoint where contamination occurred.

 

Adding to the challenge, investigators believe there could be multiple overlapping outbreaks linked to different foods rather than a single source, which further complicates efforts to trace and contain the infections.

 

Can it be treated and prevented?

 

According to the CDC, while most healthy people eventually recover even without treatment, the illness can last for several weeks or even longer, and symptoms may disappear before returning. Early diagnosis and treatment can help shorten the illness and reduce the risk of complications.

 

There is no vaccine to prevent cyclosporiasis, but it can usually be treated with the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX).

 

The CDC advises people to avoid consuming food or water that may be contaminated with faeces and to follow safe food-handling practices. These include washing hands before and after preparing fresh produce, thoroughly rinsing fruits and vegetables under running water, and refrigerating cut produce promptly. However, the agency notes that washing may not completely remove the Cyclospora parasite, particularly if contamination has already occurred.