By: Heather Williams

The recent uptick in Cyclospora infections has the Center for Disease Control and Prevention (CDC), federal, state, and local public health partners scratching their heads.  Investigations are ongoing, but a specific source has yet to be identified.  Meanwhile, uncharacteristic domestic case count keeps increasing, both in number and in affected states.  As of October 4, 2017, the CDC has information about 1,065 laboratory confirmed cases reported spanning 40 states.  At this time over half of those afflicted have no international travel history within the infectious time period.  That’s what makes this particular outbreak significant.

Cyclospora: An Unusual Domestic Concern

Cyclospora is a single-celled coccidian parasite that is known for causing diarrheal illness in humans.  Cyclospora is not known for being endemic to the United States but better known to occur in other countries.

The first American known cases were reported in the late 1970s.  These cases came from expatriates and travelers in regions of the world where Cyclospora is endemic.  As a result, cyclosporiasis, the illness resulting from infections with the Cyclospora cayetanensis parasite, was originally considered the cause of traveler’s diarrhea.  The true identity of the parasite was not fully characterized until the early 1990s, but did not get much attention until 1995 when a Cyclospora outbreak hit the United States and Canada.

The parasite is known to be endemic in Haiti, Guatemala, Peru, and Nepal, but can be found in other international areas.  If you are traveling internationally, you can check out the CDC’s travel advisory page for additional higher risk areas when traveling at

Cases in the United States, while rare, do occur.  Exposure to exotic and the less common tropical diseases seems to be increasing in tandem with the availability of faster transportation of foods from affected countries such as fresh fruit, produce, and other foods from developing countries.  With this increase is cost-effective transportation, the domestic palate is expanding to include more foods not previously accessible to the United States. This globalization of the food supply as well as changes in eating habits such as consumption of raw or undercooked foods or foods not typically in the domestic diet has contributed to introduction of domestic cases of cyclosporiasis.  Additionally, increased ease of international travel has made travel to areas that may have endemic Cyclospora more frequent than in the past.

To combat the food impact of domestic Cyclospora infection, international food trade is being monitored more now than ever before.  In fact, the Hazard Analysis and Critical Control Points (HACCP) has played an increased role in the control of food-borne illness resulting from the global food supply chain.

Cyclospora Case Update

While cases in the United States tend to increase during the summer months, this year’s Cyclospora case count is much higher than previous years.  The numbers continue to climb without a source identified.  At this time 1,025 laboratory confirmed cases have been identified.  Of that staggering number, an even more startling statistic has identified 597 of those confirmed cases have not traveled internationally during the incubation and infectious period and presented symptoms on or after May 1, 2017.  These people were likely infected in the United States and have originated from 36 states including: Arizona, California, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Washington, West Virginia, and Wisconsin.

Without a known source, the investigation continues.  Previous outbreaks of cyclosporiasis in the United States have been linked to basil, cilantro, mesclun lettuce, raspberries, and snow peas.  At this time, the CDC is not indicating avoiding any particular food, but urging consumers and retailers to continue to follow safe produce handling and cleaning recommendations.

 2017 Case History

What started as an announcement by the CDC on August 11, 2017, indicating that 570 confirmed cases had been reported across 35 states.  At this time 44% of the cases had not reported international travel.  The CDC had begun investigating this uptick in cases, as this was well beyond what is typically seen domestically.

The CDC continued to monitor laboratory confirmed cases, tracking those who had recent international travel.  By the end of August, the case count had risen to 930 confirmed cases across 40 states with 55% not attributed to international travel.

By the end of September, the CDC had reported 1,054 laboratory confirmed cases across 40 states.  At this point, a large portion of 56% were still not attributed to international travel.

This brings us to the current statistics of 1,065 confirmed cases that have been reported across 40 states and the current 56% of cases not attributed to international travel.  There is still no source identified, but the CDC, federal, state, and local health agencies are continuing to monitor and investigate this outbreak.

Significant Case Count

To begin with, this high of a case count with an illness not common in the United States is enough to raise some eyebrows.  But when you compare the historical numbers of this illness to previous years, the level of concern is serious.

Let’s talk numbers.  Between May 1, 2017 to date the United States has had 1,065 cases.  That is significant when you consider historical data.  In a study from the years 2000 to 2015 there were 1,652 cases.  In just 5 months case count has almost reached a 16-year historical total.  Most of the cases in the study occurred in 2005, with 582 of the 692 total cases that year being attributed to Basil imported from Peru.  Beyond 2005, the year of 2013 had 207 reported cases stemming from 3 separate outbreaks.  One outbreak came from bagged salad mix from Mexico, another was from imported cilantro from Mexico, and a berry salad was suspected in the third outbreak that year. The third highest year for Cyclospora occurred in 2004 with 203 cases reported.  Excluding those uncharacteristic years, there is an average of 42 cases per year.  Even with those larger outbreaks the average number of cases per year is still only 103.

Investigations are ongoing to identify the source.  UnsafeFoods will continue to monitor the situation and provide updates as they become available.