Climate change, with its longer, hotter summers, may be a contributor to an extended cyclospora outbreak, says University of California San Francisco infectious diseases specialist Dr. Peter Chin-Hong.
“Heat activates the parasite. You need heat to make the parasite infectious,” he said in a July 14 interview with American Community Media. “Summer is typically between May and August. But as that summer period becomes wider, or some places that were not as hot become hot, you may see cyclospora cases popping up in places that typically didn’t have it before.”
One in every five cities in the US now experiences at least one additional month of hotter-than-normal summer days than in 1970, according to data from Climate Central, a policy-neutral think tank.
Watery stools
Cyclosporiasis, the illness caused by a cyclospora infection, has been reported in 34 states, according to July 13 data from the Centers for Disease Control and Prevention. Thus far, 1,645 lab-confirmed cases have been reported, with 141 hospitalizations and 0 deaths. Chin-Hong believes this is an undercount of cases, as many people with severe diarrhea do not go to the hospital or to a clinic to get tested.
The highest numbers of cases have been reported in Michigan and New York. Public health officials have not yet identified the source for the outbreak, but are cautioning against eating bagged salads, unwashed leafy greens and berries. The fast food chain Taco Bell has preemptively pulled some items containing cilantro off its menu.
The infection causes prolonged severe, watery diarrhea, which does not contain blood, distinguishing it from a salmonella or e coli infection, explained Chin-Hong.
Cyclospora is spread when stool from an infected person contaminates soil or irrigation water. After spending about a week in warm environmental conditions, the parasite becomes infectious and can contaminate fresh produce, which then infects people who eat it raw. The symptoms do not show up for 7-14 days after a person has contracted the virus.
The illness is endemic in several countries in Asia, and South and Central America. In India for example, where cyclosporiasis is seasonal, infections usually occur during monsoon season, as residents eat raw, unwashed produce or drink water contaminated by heavy rains.
Here are portions of ACoM’s interview with Dr. Peter Chin-Hong, edited for length:
Dr. Chin-Hong, what are some of the factors behind the current outbreak in the US?
Cyclospora is not new. We typically see cases between the months of May and August in the United States. Summer is a good time to get cyclospora because heat activates the parasite. It makes these spores, which can become infectious.
We don’t have human-to-human transmission. People mainly get it from eating contaminated food, particularly leafy green vegetables, herbs, and berries.
We are seeing it more and more in the United States because we are relying more on these big food processing plants that take vegetables and produce from lots of different farms, and they mix it up, and then they send it to a lot of grocery stores or restaurants. So that can simultaneously affect a lot of people all at once if even one batch is contaminated.
In the early days, we only had cyclospora from people who went to a country abroad — particularly a tropical country, Central America, South America, or Asia — and came back to the United States with it. But we’re seeing more and more cases in the United States, mainly because we’re importing a lot more vegetables, and we’re using more processing plants to distribute these vegetables.
The way we’re eating food and the way we are sourcing food is changing over time, so our risk is becoming bigger in a sense.
Could you please explain how the infection is passed along?
The people who are infected have it in their gut. It passes out through the feces, but it’s not infectious at that moment. The parasite requires sitting in an environment that’s hot, and that’s why we see it mainly in the summer.
As it sits there, it turns from a non-infectious form to an infectious form in the environment. So the way that vegetables become contaminated, it’s really through feces in the soil or typically brought in from irrigation.
And then it gets into these crevices that are really hard to eliminate, mainly in berries with these little crevices, or in green leafy vegetables in a bag. It hasn’t been implicated in fruits that you can peel, like bananas and mangoes and melons and oranges.
How do we keep ouselves safe this summer as this parasite makes the rounds?
Washing your produce is not completely effective, but it can reduce the risk from berries or salads. Use whole vegetables and take off all the outer layer of the leaves. Use only the inner leaves and avoid bagged greens and salad mixes.
Cook your vegetables to 168 degrees Fahrenheit. The high temperature kills the parasite. Use fruits that have outer skin: mangoes, melons, bananas, oranges. If you take away the skin, the inside is pretty safe. That’s why you don’t really see outbreaks with cyclospora associated with those fruits.
The biggest point is not to avoid fruit and vegetables. They’re still the healthiest thing that we have in our diet.
Is it still safe to eat at a restaurant?
Eating at restaurants is still safe. Anything that’s cooked is completely safe. Anything with a peel is safe.
Not all vegetables are implicated. Once public health finds the source of contamination, we can all be a little bit more relaxed.
Are farm workers and workers at food processing plants more at risk for contracting cyclosporiasis?
Yes. Mainly because in the fields there aren’t that many facilities for washing. And sure, washing doesn’t eliminate the risk from green leafy vegetables or berries, but it reduces the risk.
And if you’re on the farm, you’re picking things, and you’re mixing it with soil that carries the parasite, that could be potentially occupational exposure. Not well recognized, but certainly very plausible.
What can farm owners and food factory processors do to keep their employees safe from a cyclospora infection?
Farm workers must have access to clean, running water. That doesn’t eliminate risk because it doesn’t take away everything, but you can reduce about 50% of the risk.
The other thing is having access to healthcare, because this kind of diarrhea is not easily identified. You need a little bit more specialized testing.
Is a treatment available?
We do actually have a treatment for cyclospora. We can give trimethoprim-sulfamethoxazole — TMP-SMX, a sulfa antibiotic — for 7-10 days, and people will get their symptoms taken care of.
If you’re immune-compromised, you may need a longer course, but it is fairly effective. And if people are allergic to a sulfa drug, there are alternatives as well.
