A mysterious parasite is spreading rapidly across America, leaving thousands with severe diarrhoea and dehydration in its wake. As of 15 July, the US Centers for Disease Control and Prevention (CDC) has confirmed a staggering 1,645 domestically acquired cases of Cyclospora infection across 34 states, with 141 hospitalisations so far. But it's not just the number of cases that raises alarm – it's also the fact that over 5,100 more are waiting to be analysed, with one state alone reporting an astonishing 3,700 cases.
The current outbreak has shed light on a decision made by the CDC last year. On 1 July 2025, the agency downgraded FoodNet, its active surveillance network, which had been in place since 1995 in collaboration with other government bodies. This change meant that tracking of Cyclospora – along with Listeria, Campylobacter, Shigella, Vibrio, and Yersinia – was no longer mandatory at all sites. Only Salmonella and E. coli remained under close surveillance. The decision to make this change, implemented without a public announcement, was only revealed after a journalist's inquiry.
Cyclospora cayetanensis is a notoriously difficult parasite to diagnose, with patients often experiencing up to 20 episodes of watery diarrhoea per day, significant weight loss, and dehydration. However, many routine stool tests do not automatically screen for Cyclospora, so a specific assay must be ordered to detect the parasite. This can lead to weeks of unnecessary suffering for patients.
Experts say that timely surveillance is crucial in controlling outbreaks like this one. As Cyclospora's oocysts take several days to mature before becoming infectious, every case can be linked back to contaminated food or water. By the time patients become ill enough for testing, the source of contamination may have been consumed or shipped elsewhere, making it harder to identify and remove affected products from the market.
While treatment is available to alleviate symptoms, the most effective way to prevent further illness during an outbreak is to quickly identify and remove contaminated food sources. Critics argue that downgrading active surveillance has made this task much more challenging, as timely and comparable case counts are no longer readily available. The CDC's justification for the change includes funding constraints and a desire to focus on core work, but some question whether these alternatives can keep pace with fast-moving outbreaks like the current one.