What we truly know about the huge US Cyclospora outbreak—and what we don’t

Combined, the two states represent more than 4,000 cyclosporiasis illnesses, making it one of the worst years for the infection. So far, 31 states have reported cases, with some noting higher numbers than usual. 

The source of the outbreak remains unknown. Cyclospora tends to spread more in the summer and has been found on “a variety of fresh produce items, both fruits and vegetables,” said Hedberg. 

In its HAN today, the CDC reports only 1,645 confirmed cases, with 141 people requiring hospitalization. The agency noted there are an additional 5,100 cases that need to be confirmed. As of yesterday, more than 400 cases in Michigan, Ohio, West Virgina, and Kentucky might represent one cluster, the CDC said, meaning the infections could be related to a common source. 

The challenge with tracking cyclosporiasis

When public health experts investigate foodborne illnesses, such as that caused by Salmonella, Listeria, or Escherichia coli O157, a lab can create a culture, grow the bacterium, and subtype it using whole-genome sequencing, explained Hedberg. The CDC then can trace the pathogen with a lab-based monitoring system known as PulseNet. 

“If there’s a multi-state outbreak of E coli O157 or Salmonella, many of those will be recognized by the CDC monitoring coming in through PulseNet,” said Hedberg. “If the CDC recognizes that there’s a multistate outbreak going on, they will coordinate investigations with all the states that have cases.” 

But Cyclospora, he says, “is a little bit different.” 

“Cyclospora is not an organism that we have the ability to grow in laboratories,” Hedberg said. “The subtyping that we might see to be able to identify what cases are related to each other is not readily available.” 

The CDC is relying on partial genotyping to connect cases of cyclosporiasis, because the “genome of the parasite is a lot more complicated,” said Gwen Biggerstaff, MPH, deputy director of the CDC’s Division of Foodborne, Waterborne, and Environmental Diseases, in a media briefing today. 

There’s often a lag in reporting from the state to the CDC, which can complicate investigations.

“As we’ve seen with this outbreak of Cyclospora, in many instances those increases will be recognized at a state level before the data gets compiled nationally to allow our federal officials to have a clear picture of what’s going on,” Hedberg said. 

Changes at the CDC and outbreak response

Last year, the CDC’s Foodborne Disease Active Surveillance Network (FoodNet) reduced the number of pathogens it tracked to two, Salmonella and Shiga toxin–producing E coli (STEC). It’s now optional for participating states to report illnesses occurring from Campylobacter,Cyclospora, Listeria, Shigella, Vibrio, and Yersinia via FoodNet. The network covers 10 sites, in which about 16% of the US population lives. 

Some have speculated that this change at the federal level is contributing to the severity of the outbreak. But FoodNet was never used to spot emerging food borne illnesses. 

“FoodNet has no role, really, to play in routinely identifying outbreaks of reportable diseases on the national level,” Hedberg said. “It’s really intended to help over time monitor trends in occurrence of these diseases so we can see from year to year whether illnesses are increasing or decreasing—so we can have better estimates for what the burden of illness associated with these pathogens might be.” 

Cyclospora is an illness reportable to the CDC. When a foodborne illness outbreak occurs, the CDC’s foodborne and waterborne disease group typically investigates it. “They are really quite good,” Osterholm said. 

Because Cyclospora is a parasite, however, a different unit at the CDC is investigating it. 

“This outbreak is being handled by the parasitic disease branch with people who are really quite inexperienced in this kind of outbreak investigation,” Osterholm added. 

Robust examination is needed to stop the spread of Cyclospora. 

“We really need to put more effort into figuring out what is actually the source,” Hedberg said. “When you have an outbreak like this, it really represents something of a public health emergency, and the response from the state and local public health agencies and the federal agencies really need to follow.” 

What to do to avoid infection

It’s difficult to tell people what to do when the cause of the outbreak remains unknown. 

“We don’t have clear information about what a likely source might be, [so] having very broad recommendations to avoid eating fresh produce, I think, potentially creates more harm than good,” Hedberg said. “The vast majority of fresh produce items that people are going to encounter are not the source.” 

If people develop persistent or severe diarrhea, they should seek medical care. There is a test for Cyclospora and medications for it. 

“There are antibiotic treatments for Cyclospora,” Hedberg said. “That can be an important way of limiting the duration of the illness.”  

What’s more, by visiting a doctor it’s more likely the case will be included in official numbers. Public health officials will contact infected people, and it’s helpful for them to participate in the investigation. 

“All the information that we have to solve outbreaks comes from the people who are involved in the outbreak,” Hedberg said. Public health officials will “look at patterns of food people have been eating over two weeks before they got ill. Where have they been traveling? What kind of other exposures they might have had.”