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Nothing sparks fear in the masses like headlines warning of an “explosive diarrhea” outbreak. According to a recent CBS News survey, about 40 percent of Americans are buying fewer fruits and vegetables due to the spread of cyclosporiasis, a parasitic illness that causes intestinal, um, distress.
The disease, which is primarily fecal-oral transmitted (aka by eating food or drinking water contaminated by human feces), is most commonly spread through fresh produce. There’s conflicting information about where the current outbreak originated (the FDA identified Taylor Farms de Mexico’s iceberg lettuce as the source, then later said it was a false positive), but bagged lettuce and fruits with lots of crevices (like raspberries and blackberries) are more likely to carry cyclospora, the parasite responsible for the illness.
As of late July, Colorado has 219 confirmed cases of cyclosporiasis, but don’t throw away all your bagged salads just yet. “We’re seeing levels that are consistent with what we see on an annual basis,” says Beth Carlton, a professor at the Colorado School of Public Health at CU Anschutz. Most of these cases—79 percent—are linked to international travel.
We asked Carlton to help us sift through the shit-uation to separate fact from fiction. She also shares insights from her new research about how climate change is affecting waterborne diseases like cyclosporiasis.
Editor’s note: The following conversation has been edited for length and clarity.
5280: How do cyclospora spread?
Beth Carlton: To put it very crudely, we get cyclospora by eating either food or water that’s been contaminated by human poop. So someone goes to the bathroom, they don’t remove the pathogen from their hand, and the food gets contaminated. This happens often in agriculture where workers may be in a field working and the toilet facilities are a long distance away. If they’re paid per piece, getting to the bathroom means lost wages. It’s a pretty hardy pathogen, so it can survive in the environment for a bit, and it really likes warm conditions.
Should we avoid eating fresh produce right now?
The biggest concern is for produce that’s uncooked, right? So, if you’re part of a vulnerable population, eating cooked produce is about as safe as it gets. The other thing is—and I think some may disagree with me—but I would say Colorado has fantastic water and sanitation infrastructure. So eating local produce is actually a great move here. Personally, I am choosing to eat lettuce rather than avoid that because it’s an important part of my diet. Washing produce is a great idea. Drying your produce after you wash it can just add one more level of trying to remove things, either in a salad spinner or with a paper towel.
You recently published a study, with the help of researchers at the University of Washington School of Public Health, about how climate change is impacting waterborne diseases, like cyclosporiasis. What did you find?
What we found is that climate change is altering the distribution of waterborne diseases. The relationship between climate and waterborne diseases varies by pathogen. So, viruses are impacted in different ways than bacteria, for example. Viruses actually do really well in cool, dry conditions. A warmer climate is not necessarily going to mean more norovirus or rotavirus, so that’s good news. But bacteria thrive in warm conditions, and so warmer temperatures—up to some sort of threshold—could translate to more diarrheal waterborne diseases.
We also found things like hurricanes and flooding can lead to increases in waterborne diseases. Flooding can destroy infrastructure and lead to lots of contact with contaminated water. Things like hurricanes that lead to flooding can also lead to people crowding into shelters, and that leads to waterborne disease outbreaks due to crowded conditions.
Your study also found that drought can actually lead to an increase in waterborne diseases. Why is that?
In drought conditions where people don’t have good access to water and sanitation infrastructure, you have more people and more animals using fewer water sources that are more likely to be contaminated—so it’s like this concentration effect. Another thing we’ve learned is that if you have a drought or extended dry period and then a heavy rainfall event, that heavy rainfall event can wash all sorts of contaminants into water sources. So those heavy rainfall events that come after long dry periods can be the most risky in terms of water quality.
Places like Colorado generally have the infrastructure to handle those pulses of pathogens, but moving forward, we need to make sure that we continue to be able to respond to these spikes. But if you’re in the backcountry and reliant on surface water sources, that heavy rainfall right after dry periods is more likely to be contaminated.
So we should always filter our water in the backcountry—even alpine water?
Yeah, stuff breaks down real slow up there. I always treat my water.
What specific pathogens might we see increased outbreaks of if climate change continues to worsen?
For waterborne pathogens, the ones that we are paying attention to are giardia, cryptosporidium, and the bacterial pathogens that are largely foodborne, like salmonella and campylobacter. They’re all really unpleasant. Anyone can be infected, but people who are immunocompromised—the very old, the very young—are the most vulnerable and can have pretty severe effects.
How prepared is Colorado to handle this potential increase in outbreaks?
In general, Colorado has great public health infrastructure. However, it is being impacted by federal cuts. So our ability to track infectious diseases and respond to them is very much contingent on us having a public health workforce that is trained and staffed appropriately.
I think it is really important we are investing in public health infrastructure. This means public health workers, public health data systems—it’s not always the really sexy stuff. But we need to make sure we have the workforce and the innovation so that we can identify where these outbreaks are happening and intervene early.
For more information about cyclosporiasis, including the current number of confirmed Colorado cases, visit the Colorado Department of Public Health & Environment’s website. The data is updated every Monday.
