Epidemiologic Notes and Reports Streptococcal Foodborne Outbreaks -- Puerto Rico, Missouri
Two large outbreaks of foodborne group A streptococcal pharyngitis have been reported to CDC during 1984 in Puerto Rico and Missouri.
Puerto Rico: On August 3, 1984, an outbreak occurred among guests attending a party in a private home in San Juan, Puerto Rico. During that weekend, numerous party attendees became ill with sore throat, myalgia, cervical adenopathy, and fever. Many were seen by physicians and had exudative pharyngitis. One was hospitalized.
The Puerto Rico Department of Health was notified of the outbreak on August 8. Because of the high attack rate and the clustering of cases, the outbreak was presumed to be foodborne. Self-administrated questionnaires were received from 45 (96%) of the 47 party attendees, and 25 questionnaires were received from their household contacts. Throat cultures were obtained from 44 (94%) of party attendees.
Four persons were excluded from the questionnaire analysis--three because of onset of pharyngitis before the party, and one, because of an incomplete questionnaire. Of the 41 remaining persons, 23 (56%) had illness meeting the case definition. The attack rate for persons who ate carrucho, a conch salad, was 70%, compared with 29% for persons who did not eat carrucho (p = 0.013). No other food showed significantly different attack rates. No dose-response effect for persons eating carrucho was demonstrated, nor was a difference in attack rates observed between persons who ate early in the evening and those who ate later in the evening. That carrucho was the vehicle for transmission was further supported by the fact that two of four persons who did not attend the party but who ate carrucho that had been brought home to them became ill with pharyngitis. The secondary attack rate for household contacts who did not eat carrucho was 4%. The incubation period was 12-60 hours (median 24 hours).
Throat cultures from 11 party attendees grew group A streptococci, as did a small sample of carrucho remaining from the party. All cultures were of the same serotype (M nontypable, T12, SOR+).
The carrucho was prepared in a small beachside restaurant outside San Juan. The conch used to make the carrucho came in a torn, unlabeled plastic bag and was allegedly imported from Santo Domingo. None of the uncooked conch remained for testing, but the method of salad preparation, which reportably included boiling the conch for 2 1/2 hours, should have been adequate to kill any streptococci. Seventy pounds of carrucho was made the afternoon of the party. The 25 pounds purchased by the party's host was left in an automobile at ambient temperature for 3 hours before delivery to the party.
Approximately 2,000 persons who ate in the restaurant that weekend were potentially exposed to the 45 pounds of remaining carrucho. Because there was no way to identify individuals who might have eaten there that weekend, four clinical microbiology laboratories serving the San Juan area were surveyed in an attempt to determine if the number of positive throat cultures in August was higher than the number during the same time the previous year; no increase was observed.
All foodhandlers at the restaurant were interviewed and examined for skin lesions, and cultures (pharyngeal, nasal, and hand) were obtained. No cultures were positive, and no histories were obtained of recent pharyngitis or skin lesions. Food prepared at the restaurant, including carrucho, during the week after the party was cultured; all was negative for group A streptococci.
Because party attendees were potentially exposed to streptococci, the Puerto Rico Department of Health recommended that all attendees who developed symptoms of pharyngitis, regardless of culture results, receive antibiotic therapy effective against group A streptococci.
Missouri: Another outbreak occurred among participants from seven states at a meeting held at a Kansas City, Missouri, hotel from May 31, to June 1, 1984. On June 6, the Kansas City Health Department was notified of three cases of group A beta-hemolytic streptococcal pharyngitis occurring in three technicians from one blood bank who had attended the meeting. Other cases were subsequently reported among persons who attended the meeting. Clustering of cases and a high attack rate suggested a foodborne source.
A questionnaire was administered by telephone or mail to 136 (98%) of the 139 persons identified as having attended the conference. Cases were defined as persons with acute onset of sore throat between May 31 and June 5, who had had no antecedent contact to household members with pharyngitis. Severity of illness ranged from minor discomfort to symptoms resulting in several days' absence from work. Positive cultures for group A streptococci were reported for 13 (93%) of 14 individuals from whom throat cultures were obtained. However, none of the cultures were still available for typing or confirmation by the time of investigation. The survey implicated a luncheon held May 31. Sixty (57%) cases among the 106 persons who attended it were identified, compared with no cases among 30 conference attendees who did not attend the luncheon (p 0.0001). Food-specific attack rates suggested macaroni salad or mousse as possible vehicles of transmission. The attack rate for persons who ate macaroni salad was 88%, compared with 47% for those who did not (p 0.0001), but only one-third of persons who were ill gave histories of having eaten macaroni salad. The attack rate for persons who ate mousse was 63%, compared with 39% for persons who did not (p = 0.053), and, since 82% of ill persons reported having eaten the mousse, it was considered more likely if only one vehicle were involved. The incubation period of the illness was 24-36 hours (median 36 hours).
All the food for the luncheon was prepared by five hotel employees. The foodhandlers were interviewed and examined, and cultures were obtained. All were negative for group A streptococci, and no visible skin lesions were found on any worker. One worker claimed to have had a sore throat the day of the luncheon but did not seek medical attention.
The pastry chef had prepared two types of mousse the morning of the luncheon. Although it was refrigerated for 30 minutes during one phase of preparation, the final product was kept at room temperature for 1-2 hours before the luncheon. Reported by JG Rigau, MD, Commonwealth Epidemiologist, Puerto Rico Dept of Health; T Martin, V Gibson, D Giedinghagen, GL Hoff, PhD, Div of Communicable Disease Control, Div of Environmental Health, Kansas City Health Dept, HD Donnell, Jr, MD, State Epidemiologist, Missouri Dept of Social Svcs; Respiratory and Special Pathogens Epidemiology Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.
Editorial Note: Before the advent of pasteurization of milk and availability of adequate refrigeration, foodborne streptococcal outbreaks were very common. Outbreaks resulting in epidemics of scarlet fever, rheumatic fever, and suppurative complications were reported. Improvements in sanitation have resulted in foodborne streptococcal outbreaks becoming relatively uncommon (1-3).
These outbreaks show the difficulties involved in recognizing foodborne illness. Foodborne transmission of streptococci, rather than person-to-person transmission, is suggested by a large clustering of cases, a shorter incubation period, and a higher attack rate. Unless disease occurs in a setting where people who are ill are likely to notice the epidemic themselves, it is difficult for public health officials to detect the increased incidence of streptococcal pharyngitis in the community, especially since only a small percentage of persons with sore throats seek medical attention and ultimately receive treatment for the illness. The Puerto Rico outbreak was recognized only because a number of ill people worked in the same office. Initially, the party attendees felt the illness resulted from close person-to-person contact; only when persons who were not at the party ate party food and became ill did the office manager notify the health department. The second outbreak almost escaped detection, since the illness peaked after the conference had ended, and the participants had returned to their homes in seven states.
It is unknown how many cases of endemic streptococcal pharyngitis are caused by foodborne transmission. It is important to recognize that rheumatic fever and glomerulonephritis may result from outbreaks of these infections.
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