Reference no: EM133243645

Case study - Outbreaks in Other States

Despite recommendations by health departments in Texas and Ontario to wash strawberries carefully before eating them, cases of cyclosporiasis continued to occur nationwide. By the end of June, over 800 laboratory-confirmed Cyclospora infections were reported to the CDC from 20 states, the District of Columbia, and two Canadian provinces (FIGURE I-6).

Discrepancies began to appear in the link between California strawberries and the Cyclospora infections. Investigations undertaken by the New York City Health Department and the South Carolina Department of Health and Environmental Control pointed toward raspberries as the source of the cyclosporiasis outbreaks in their jurisdictions. In late June, the New Jersey Department of Health and Senior Services (NJDHSS) initiated an epidemiologic investigation to identify the source of infection among cyclosporiasis cases in New Jersey residents. The cases to be included in the New Jersey study were not linked together by a common event and did not occur in a well-defined group of people. To assess possible risk factors for infection among the cases of cyclosporiasis in New Jersey, NJDHSS conducted a case-control study. In contrast to the Texas investigation, a case of cyclosporiasis for this study was defined as a patient with laboratory-­confirmed Cyclosporainfection and a history of diarrhea. For the New Jersey case-control study, cases were identified by reviewing laboratory records from all clinical laboratories in the state. Forty-two cases were identified. Two controls were identified for each case through telephone calls to randomly selected households in the community. To be eligible for the study, controls could not have had loose stools during the previous 30 days. Investigators interviewed 30 case patients and 60 controls by telephone using a standardized questionnaire that asked about possible exposures (including consumption of 17 fruits and 15 vegetables, water and soil exposures, and animal contact) during the period of interest.

Case patients and controls were similar with respect to age, sex, and level of education. Twenty-one (70%) of 30 case patients and four (7%) of 60 controls had eaten raspberries (see TABLE I-4). The odds ratio for eating raspberries was 32.7 (p value < 0.0001). No other exposures (including strawberries) were associated with illness.

Studies from other states and Canada supported the results from New Jersey, New York City, and South Carolina. A total of 725 cases of cyclosporiasis associated with 55 different events (e.g., wedding receptions, parties, buffets) were investigated. The only exposure consistently associated with cyclosporiasis was the consumption of raspberries. Raspberries were served at 54 of the 55 events and were the only berries served at 11 events. (Reexamination of the events associated with the initial outbreaks in Texas and Ontario indicated that raspberries were included among the implicated berry items served at those events.) The median attack rate for cyclosporiasis among persons who ate items that contained raspberries at the different events was 93%. Furthermore, for 27 of the 41 events for which adequate data were available, the associations between the consumption of raspberries and cyclosporiasis were statistically significant (p value < 0.05). The origin (i.e., producer) and mode of contamination of the raspberries served at the events were unknown. Because of the large number of raspberry producers at the time of the outbreaks (both domestic and international), public health officials could not recall the implicated raspberries or remove them from the marketplace. Traceback investigations were planned

Question 1: Based on the knowledge learned in this chapter (study designs), would you undertake a case-control or a cohort study to investigate the source of the cyclosporiasis cases in New Jersey? Why?

Question 2: How might you identify cases of cyclosporiasis for the case-control study? Who would you use as controls?

Question 3: interpret the results of the New Jersey case-control study.

Question 4: Would you alert the public of this possible public health threat? Justify your response.