The Summer of Cyclospora: APHL’s Food Safety Team Answers Important Questions About the Outbreak and the Response

Cyclospora is a microscopic parasite that infects humans when they eat food or drink water contaminated with Cyclospora-infected fecal matter. The severe—and potentially deadly—intestinal illness Cyclospora causes is known as cyclosporiasis, and while cases typically rise during the warmer months, this summer Cyclospora has taken the country by storm.

Since May 1, the US Centers for Disease Control and Prevention (CDC) has reported over 17,000 laboratory-confirmed cases of cyclosporiasis acquired here in this country—compared to just 1,180 from May to August 31 last year—and the numbers continue to climb. More than 900 patients have been hospitalized and two have died. Another roughly 12,000 cases have been reported but either haven’t been confirmed or are under further investigation. And, say experts, actual case numbers are likely higher, as many people never see a doctor for the illness, so their cases go unreported.

Many of this summer’s cases have been linked to iceberg lettuce imported from Mexico; the product has subsequently been recalled. But CDC and FDA are investigating multiple clusters of Cyclospora unrelated to the lettuce outbreak. Thus far, a total of 48 states and the District of Columbia are reporting cases. Playing a crucial role in investigating those cases are the nation’s public health laboratories.

What do you need to know about the outbreak and the response? We sat down with APHL’s Food Safety team to get the answers.

Why has there been such an unusually high volume of specimens to test?

 “The combination of a large outbreak, heightened surveillance and improved detection has created a substantial workload across clinical, commercial and public health laboratories,” said APHL’s Shari Shea, senior director, Food Safety. “Increased detection of patient illnesses also means more positive specimens and information moving through public health systems for surveillance, outbreak investigation and, when appropriate, additional characterization."

Speaking of workload, how are public health laboratories adapting workflows and capacity during this response?

The answer is multifold. Depending on needs, some labs are reprioritizing specimens, reallocating staff, streamlining specimen submissions and processing, and increasing testing capacity. There’s also been closer coordination between clinical, commercial and public health laboratories, which means specimens and information can move through the entire system more efficiently.

When it comes to testing for Cyclospora, what are some obstacles?

Cyclospora is a particularly difficult organism to work with. For starters, Cyclospora may not be detected through routine stool testing methods. It also can’t be grown in a laboratory, and because one particular sample may not contain enough of the parasite’s shedding oocyst (a microscopic egg-like structure) to be picked up through routine testing methods, multiple stool samples may need to be examined to confirm an infection.

Laboratories can use microscopy and molecular methods, including PCR, to detect Cyclospora. When used in conjunction with epidemiological information, the addition of targeted genotyping can help scientists determine which cases in an outbreak may be related. But molecular data alone can’t establish a common source. Currently, there is no whole genome sequencing method available that can link Cyclospora cases to a contaminated product the way scientists can link bacterial pathogens such as Salmonella.

“Laboratories need trained personnel, appropriate specimen-processing workflows and validated methods to produce reliable results,” Shea explained. “During a surge, hands-on steps such as specimen preparation and nucleic-acid extraction can limit how quickly laboratories can increase throughput, even when testing instruments are available.”

What makes finding the source of a Cyclospora outbreak so challenging?

First, it can take days to weeks for symptoms of cyclosporiasis (e.g., watery stools, nausea, stomach cramping and bloating) to appear after eating or drinking something contaminated with Cyclospora—and that can be a long time for people to remember exactly what they consumed prior to their illness. What’s more, fresh produce (past outbreaks have largely been linked to fresh fruits and vegetables) can move through complex distribution systems and may be served as just one ingredient within a multi-ingredient meal.

What do laboratories need as the response continues, and how is APHL supporting them?

Laboratories need clear and timely guidance about specimen submission and prioritization so limited capacity can be directed toward the specimens most useful to the investigation, said Shea. They also need sustainable surge capacity, including trained personnel, appropriate testing and extraction resources, timely molecular analysis and reporting, and clear information about available funding and allowable uses.

Shared technical resources are also important, Shea added. Access to validated methods, extraction approaches, appropriate control materials and lessons learned from other laboratories can prevent jurisdictions from having to solve the same technical problems independently.

APHL's role is to help translate what laboratories are experiencing on the ground into coordinated support. To that end, APHL is connecting public health laboratories with one another and with federal and other response partners so that emerging needs, challenges and solutions can be shared quickly. At the same time, APHL is coordinating across the public health, clinical, agricultural and food-testing components of the response, including communication with CDC and FDA partners.

“One of our goals is to make it easier for laboratories to learn from one another throughout the response,” summed up Shea. “Continued communication among public health laboratories and federal, state, clinical and regulatory partners will remain essential as the response evolves.”