Lessons Learned Again: Cyclosporiasis and Raspberries

• Coccidiosis
• Fruit
• Raspberries
• Disease outbreaks
• Guatemala

It has been almost 2 years since I was asked to write an editorial to accompany an article by Herwaldt and colleagues entitled “An Outbreak in 1996 of Cyclosporiasis Associated with Imported Raspberries” (1). My editorial detailed important lessons learned in that original investigation and suggested what efforts might be needed to prevent such outbreaks in the future (2). The occurrence of a second and similar outbreak, described by Herwaldt and colleagues (3) in this issue, prompts another look at foodborne illness and what must be done to prevent it.

Herwaldt and colleagues are to be congratulated for this comprehensive and careful outbreak investigation, which confirmed Guatemalan raspberries as the vehicle for Cyclospora cayetanensis(3). Many of their findings are similar to those reported in the 1996 outbreak investigation. One notable finding is that case exposures generally consisted of only a few raspberries, but the median attack rate among persons who ate raspberries was 91.7%. This suggests a very low infectious dose for C. cayetanensis and relatively uniform contamination of the implicated raspberry lots. It is unlikely that such contamination of raspberries would result from contact by an infected worker; rather, it seems more likely that an environmental reservoir is responsible. Contaminated water used for irrigation or pesticide spraying continues to be an important consideration. Contamination of raspberries through exposure to bird or insect droppings also remains a possibility.

It is clear that the control measures instituted after the 1996 outbreak were inadequate to address the actual source of contamination. Even after the 1997 outbreak described in this issue, cyclosporiasis from imported berries continues to recur. The U.S. Food and Drug Administration (FDA) did not permit the importation of fresh Guatemalan raspberries into the United States in the spring of 1998; importation into Canada continued, however, and outbreaks linked to these raspberries occurred in Ontario in May 1998 (4).

Herwaldt and colleagues concluded that the 1997 outbreak investigation highlights the need for improved surveillance for foodborne illness (3). Although this conclusion may seem obvious, it is only a small piece of the public health effort needed to reduce the incidence of foodborne illness through a rapid outbreak response. An outbreak of cyclosporiasis associated with the importation of Guatemalan raspberries was anticipated in the spring of 1997, and many state and local department surveillance systems were primed for the identification and the epidemiologic investigation of such cases. Even though case clusters were reported in association with the events as early as 1 April 1997, it took the FDA until 28 May 1997 to stop shipments of Guatemalan raspberries into the United States. Given this response time from recognition to control, improved surveillance will not make a substantial difference on the eventual case numbers without faster tracebacks of product to a specific location and timely regulatory action.

As I concluded in my previous editorial, the most crucial lesson to be learned from the story of cyclosporiasis associated with imported raspberries is that irradiation should be used to achieve ionizing pasteurization of food. Herwaldt and colleagues (3) conclude that it is unclear whether Cyclospora species are susceptible to the doses of γ irradiation permissible for use on food in the United States; two parasitic agents previously studied for that purpose ranged from susceptible to resistant to such treatments (5, 6). However, to date, only one study has suggested that Eimeria species may be resistant to irradiation at levels of 1 kilogray or lower (the current level permissible by the FDA for treatment of produce). In contrast, at least 18 different studies in the medical literature report that Eimeria species are inactivated by irradiation at levels less than 1 kilogray, and an additional 7 studies support that conclusion for Toxoplasma species. Irradiation at levels less than 1 kilogray will be limited in the ability to inactivate common foodborne bacteria. However, the overwhelming body of available data suggest that irradiation at the approved level is appropriate to control Cyclospora and contamination of raspberries by other parasites. To maximize the public health benefit of irradiation, urgent additional research must be conducted and the necessary petitions submitted to the FDA for approval for higher levels of irradiation to be used on produce.

When I ask the wholesale and retail food service industry why they do not actively pursue the use of irradiation, the most frequently cited reason is lack of leadership at the federal government level to promote this as an important public health technique. The food service industry fears the well-known techniques of commercial terrorism that activist groups use to wrongly proclaim that irradiation is unsafe or seriously compromises the quality of food products. The tactics of these groups will not be addressed until a strong voice and detailed blueprint for irradiation come from our federal food safety agencies. Such leadership, however, is currently missing. Until then, as much as we talk about the need for increased safety of our food supply, we will continue to see our rhetoric, actions, and outcomes in disarray.

• Copyright ©2004 by the American College of Physicians