FDA Grand Rounds: Cyclospora cayetanensis

Subsequently, the FDA created a novel multidisciplinary method to aid in detecting C cayetanensis in food, which they called BAM 19b. It is composed of 3 steps:

1. Washing the food with a reagent to recover the oocytes of C cayetanensis.

2. DNA extraction from the above concentrated material.

3. Identification of the species of Cyclospora via real-time polymerase chain reaction.

This method has been validated for other matrices, including shredded carrots, basil, parsley, and bagged romaine lettuce. In July 2018, the FDA implemented this method in all of its food and field labs.

C cayetanensis: a foreign or domestic problem?

After the consecutive outbreaks between 1999 and 2000, and the large outbreak in 2013, there was a thought that C cayetanensis may be an imported problem, as the sources in all of the outbreaks were foods imported from developing nations with farms that may not have standards to prevent contamination with C cayetanensis. The outbreak in 2014, wherein 304 cases were confirmed, was investigated by epidemiologic and traceback studies in infected people in Texas and fresh cilantro imported from Puebla, Mexico, was implicated. Cilantro was also demonstrated as the food vehicle for an outbreak in 2015 (546 cases in 31 states).

A ban on importing suspected and historic food sources of C cayetanensis was implemented and in 2016, there was a demonstrated decrease in cases of the parasitic infection. However, this theory was soundly disproved by a large outbreak in 2017 wherein in there were 1065 laboratory-confirmed cases of C cayetanensis infection in 40 states; 56% of cases had no history of international travel and no specific food source was definitively identified.

In 2018, there were a total of 2299 laboratory-confirmed and domestically acquired cases of C cayetanensis across 33 states. Of note, 511 of these cases across 15 states were linked to McDonald’s salads and 250 cases across 4 states were associated with Del Monte Fresh Produce vegetable trays. Multiple clusters across all cases were associated with cilantro and basil. On July 28, 2018, for the first time, researchers at the FDA were able to detect presence of C cayetanensis via in an unopened bag of salad delivered to McDonalds.

This outbreak triggered many more investigations to detect C cayetanensis in food samples. Two of these investigations detected C cayetanensis in domestically grown romaine lettuce; these samples were not linked to the outbreaks. However, this represented the second time that C cayetanensis was identified in domestically grown produce, solidifying that this may not entirely be an imported problem.

Genomics and Molecular Epidemiology of C cayetanensis

Samples from the 2018 outbreak allowed researchers at the FDA to apply preliminary mitochondrial markers for C cayetanensis,which the researchers advised should be used as supplementary evidence in the effort to detect and identify Cyclospora that had been detected by another method.

The CDC has also done deeper research on genotyping of Cyclospora. Preliminary results of these studies suggested a multilocus sequence typing tool that may help in identification of C cayetanensis. However, further investigation in larger samples showed that this tool had a high variability, and many specimens could not be assigned a type because of poor quality of DNA sequencing at >1 loci.

Variability of the mitochondrial genome sequences allows for separation of different groups of Cyclospora. Moreover, this technique allowed for geographic separation and identification. That is, sequences of Cyclospora from Maine were different from those in Ohio and those in Indonesia or Nepal. This may allow researchers to identify a source location for the parasite.

In an effort to use these data, Dr da Silva noted that the FDA is currently building a database, called CycloTrakr, to track species of Cyclospora across different geographic regions that have previously been linked to C cayetanensis outbreaks.

Importantly, molecular epidemiology will also allow scientists to link outbreaks into clusters, including outbreaks that were not previously linked to any known cluster.