Epidemiology

Patterns of Infection
Recent Outbreaks
Public Health and Prevention

Patterns of Infection

Cyclospora has now been described and associated with diarrheal illness in North, Central and South America, the Caribbean, Africa, Bangladesh, Southeast Asia, Australia, England, Spain, and eastern Europe. Areas endemic with cyclosporiasis are mainly in Central and South America and Asia. Infections can occur sporadically or in clusters. Most infections occur in these endemic areas or in travelers returning from these regions. Much of the information about Cyclospora comes from study groups in Nepal, Haiti and Peru. However, infections and outbreaks indigenous to other areas, including recent outbreaks in the United States, have been reported. The prevalence of Cyclospora in North America and the United Kingdom is estimated at levels lower than .5%.

Cyclospora infection appears to be very seasonal, although it has different patterns in different parts of the world. Certain ranges of temperature, humidity and other environmental factors appear to allow for survival of oocysts and sporulation. In Nepal and Kathmandu it coincides with the rainy season from May through September. In Haiti infection is more common in the drier and cooler months of the first quarter of the year. In coastal Peru, infections occur mainly from December through May and sometimes into June or July. In Guatemala, research shows a peak in June but a heightened incidence from May through August. In Indonesia the peak season for the parasite is during the wet season of October through May.

In many cases the method of transmission and the source of water or food contamination is unknown so it is difficult to gain a full understanding of the connections between the parasite, the environment and the human host. In controlled studies in endemic areas it has been shown that many factors including the area of the world, specific community, sanitary conditions, season, and personal attributes like age, socioeconomic status, and immune competence can influence the chance of a symptomatic infection and the severity of the disease. Immunity has been shown to develop with repeated exposure to the parasite and natives to an endemic region have been shown to have greater incidence of asymptomatic or mild infections.

There has been a major increase in the number of reported cases of cyclosporiasis since 1995. The recent foodborne outbreaks in the United States have drawn more attention to this newly discovered parasite. The connections with imported fresh produce, especially Guatemalan raspberries, have highlighted the fact that the supply of fresh produce in the United States is becoming increasingly international.

Recent Outbreaks

The first documented cases of cyclosporiasis occurred in three patients in Papua New Guinea in 1977 and 1978 and were reported in 1979 by Ashford.

In the 1990’s there have been at least 11 documented foodborne outbreaks of cyclosporiasis in North America affecting at least 3600 people. The actual number of infections and outbreaks is probably significantly larger because this disease has only recently been described and underrecognition and underreporting are likely to be prominent.

The first documented US cases were noted in four travellers returning from Haiti and Mexico in 1986. The first outbreak in the United States was recorded in at Cook County Hospital in Chicago. This outbreak was apparently caused by contamination of a water storage tank by an unknown means.

A major outbreak occurred in the United States and Canada in the spring and summer of 1996. Cases of cyclosporiasis were reported in 20 States, Washington D.C and 2 Canadian provinces and the estimated total of infected persons was 1465. This number was greater than the total number of cyclosporiasis cases that had been reported worldwide thus far. Half of the cases were cluster related and most could be traced to specific social events that occurred from May 3 through June 14, 1996.

After much epidemiological investigation, the source of the outbreaks was found to be raspberries from Guatemala. Although contaminated raspberries were never directly discovered, epidemiological trace-back methods found raspberries to be the most likely source of infection. The patterns of distribution suggest that the raspberries were contaminated in Guatemala before being imported by the United States. The seasonality of the outbreak also corresponded with the peak infection times in Guatemala. The ultimate source of contamination of the raspberries is uncertain although possibilities such as fecal contamination of water used for spraying fungicides have been suggested. Because of the long period and favorable conditions required for sporulation, the raspberries were probably contaminated in Guatemala with oocysts that were sporulated or close to sporulating.

There were no documented cases of cyclosporiasis associated with Guatemalan raspberries in the winter months of 1996-97. In preparation for the next spring export season, the Guatemalan Berry Commission began a program to improve hygiene, sanitation, and the quality of water used on berry farms. Only farms that met this commission’s approval were allowed to export raspberries to the United States. Despite these control measures, another multi-state outbreak of cyclosporiasis occurred in in 1997. Import of raspberries from Guatemala was then stopped for the remainder of the spring season. In the following spring under guidance of the FDA, the United States blocked all raspberry imports from Guatemala and there were no more cases.

The raspberry-associated outbreaks of 1996 and 1997 highlight the increasing international aspect of US fruit and vegetable imports, especially the marked increase of raspberries from Guatemala in the mid 1990’s. It also demonstrated that consumption of very few raspberries could result in infection, as some patients became infected after eating only a few berries used as a dessert garnish.

In April and March of 1997 there were other outbreaks in the United States associated with consumption of fresh mesclun. The source of this mesclun was traced to Peru. The timing of these outbreaks correlated to the peak season of human infection in Peru.

Two sets of outbreaks, in 1997 and in 1999, were later traced to fresh basil. The first cluster centered around the North Virginia/Washington DC/Baltimore area and the second in Missouri. This outbreaks occurred later in the year than those associated with raspberries. Unlike the case with the earlier raspberry-linked outbreaks, the first basil outbreak could potentially have been contaminated within the United States. All infections were traced to a particular chain of gourmet food stores, although many other places received basil from the same supplier. The first of two emerging explanations for this discrepancy is that the basil was contaminated in the United States by food preparation workers and allowed to sit out long enough for the oocysts to sporulate and become infectious. The second explanation is that all of the supplier’s basil was contaminated but only this chain of stores allowed the basil to sit out or be stored in subuptimal refrigeration for long enough before being served for sporulation to occur.

The basil-associated outbreak in Missouri was probably contaminated in the farm of origin, either in the United States or in Mexico. This outbreak was associated with the first positive identification of Cyclospora parasites in an epidemiologically linked food item. Cyclospora was detected in leftovers from one of the parties that resulted in a cluster of cyclosporiasis cases.

Public Health and Prevention Strategies

There is no vaccine available for Cyclospora infection. Proper hygeine, sanitation, treatment and filtration of water and hygienic preparation of food could prevent many cases of Cyclospora in endemic areas. Foodborne outbreaks could be limited by washing fruits and vegetables before serving, although laboratory tests with lettuce show that washing might not eliminate all of the parasites. Cyclospora cases are on the list of infections that should be reported to the CDC. A better understanding of the properties and epidemiology of this parasite could lead to better methods of control and prevention strategies.

*pictures courtesy of the CDC, www.landmarks.org/ ten_most_2_copy.htm and www.studyabroad.com/content/portals/ maps/guatemala_map.html.