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Epidemiologic Notes and Reports Common Source Outbreaks of Trichinosis -- New York City, Rhode Island

Forty-six cases of trichinosis including 1 death were diagnosed in the period November-December 1981 in 3 common-source outbreaks reported from New York City and Rhode Island. All 3 outbreaks were associated with eating pork from hogs purchased directly from farms and prepared in ethnic dishes calling for raw or partially cooked pork.

New York City: Eight cases of trichinosis were reported to the New York City Department of Health from 2 Brooklyn hospitals on November 16, 1981. The patients were members of 3 related families of Italian heritage. A ninth case was subsequently diagnosed in the course of the investigation. One patient died. The outbreak appeared to be associated with eating dried, homemade pork sausage.

The index patient was a 55-year-old woman who had onset of symptoms on November 4, 1981, 10 days after eating some of the pork sausage. Her initial symptoms included nausea, vomiting, diarrhea, myalgia, and abdominal pain. When she became febrile, she was hospitalized. By the nineteenth day of hospitalization, the patient had developed bronchopneumonia, pulmonary edema, paralytic ileus, and motor paralysis; she died the same day. Autopsy findings revealed bronchopneumonia, pulmonary artery thrombosis, pulmonary edema, mild cardiomegaly and chronic myocarditis, hepatomegaly, and renal vein thrombosis. No Trichinella larvae were identified in the brain, although fresh thromboses were noted in blood vessels. Multiple muscle samples were positive for Trichinella.

The other 8 patients had eaten dried, uncooked, or lightly fried sausage on 2 occasions, November 4 and 11. Onset of symptoms ranged from 2 to 13 days after eating the initial serving of sausage. Of the symptoms commonly associated with clinical trichinosis, all patients had fever (temperatures ranging from 37.9 C to 39.1 C (100.2 F to 102.4 F)), periorbital edema and muscle pain. Six of 8 patients had abdominal pain; 5 of 8 had diarrhea. Two patients reported headache, and 2 had subconjunctival hemorrhages. Most patients received oral or intravenous steroid therapy; at least 2 also received thiabendazole. Laboratory studies revealed that all of the 8 patients whose blood was examined had eosinophilia (range 4%-57%). Six of 7 patients whose specimens were tested for antibody to Trichinella with the bentonite flocculation (BF) test had titers compatible with recent infection ( greater than or equal to 10), and 3 patients from whom additional specimens were tested approximately 7 weeks after onset of symptoms had a greater than or equal to 4-fold rise in titer to Trichinella.

Interviews with family members revealed that the sausage had been prepared from a pig purchased and slaughtered at a farm in Green County, New York. Two other pigs kept at the farm over the past year had been slaughtered for consumption by the farm owner. The carcass of the pig that had been purchased was brought to New York City, where it was hung and dried indoors for 2 days; the carcass was then butchered, and sausages were prepared and hung to dry for another 10 days. The sausages were then eaten raw by 8 patients. The ninth patient fried the sausage lightly before eating it. Samples of sausage were examined by the hospital pathologist, who identified multiple encysted larvae of T. spiralis.

Sausage prepared by the farmer with meat from the other 2 pigs was examined at the Animal Parasitology Institute, United States Department of Agriculture (USDA), and found to contain Trichinella. The farmer insisted that the pigs had been fed only grains. However, the farmer went hunting frequently and fed portions of killed game to pet dogs. It was not known whether the pigs had also eaten portions of such meat.

Rhode Island: On November 23, 1981, the Rhode Island Department of Health was notified by the Indochinese Unit of the State Department of Social and Rehabilitative Services of an outbreak in that state. A group of Kampuchean refugees were experiencing swollen eyes, myalgia, and fever; several had been hospitalized. The symptoms plus eosinophilia and elevated creatine phosphokinase (CPK) levels suggested trichinosis; this diagnosis was confirmed on the basis of findings from a muscle biopsy performed on 1 hospitalized patient. An investigation begun November 24 showed that on October 15, 11 Kampuchean families had shared a meal in the home of 1 family. The main dish was spiced, boiled meat and viscera of a pig that had been purchased the same day from a local farm. Forty-nine family members reported eating the pork either at that meal or subsequently at their homes. Between November 11 and 28, 26 persons became ill with signs and symptoms that included fever and either myalgia or periorbital edema.Trichinosis was confirmed for 24 of the 26 ill persons on the basis of positive BF titers (ranging from 5 to 640) measured in serum specimens obtained between 48 and 75 days after the shared meal. The other 23 asymptomatic family members were negative for trichinal antibodies. Five of the most severely ill persons were hospitalized; serum CPK values for these patients ranged from 544 to 7,360 International Units (IU). Of the 24 trichinosis patients, who ranged in age from 2 to 66 years, 15 were male. All symptomatic individuals recovered without specific therapy. Staff of the Animal Parasitology Institute, USDA, investigated the farm from which the implicated pig had been obtained. The farmer stated that he only kept a few pigs at a time and that they were not fed garbage. A land-fill dump was located approximately 2 miles from the farm. Four hogs purchased from the farmer were killed, and the tissues were examined by direct microscopy and digestion of tissues. Blood samples were taken from 5 other pigs for serologic tests. All tissues and serum specimens were negative for Trichinella in these tests. Thirty-two rats trapped and killed on the farm were negative for Trichinella larva.

A second outbreak occurred in Rhode Island in early December 1981. The Rhode Island Department of Health was notified by staff at a hospital emergency room of a group of Laotian refugees with trichinosis-like illness. Investigation revealed that on November 24, 30 members of 4 extended families had shared a meal that included raw pork from a pig purchased at the same farm involved in the first Rhode Island outbreak discussed above. Between December 10 and 29, 13 of these 31 persons became ill with signs and symptoms including fever, periorbital edema, myalgia, eosinophilia ( greater than or equal to 10%), and elevated serum CPK levels ( 250 IU). Four patients were hospitalized, and T. spiralis larvae were identified in material from muscle biopsies performed on 2 women ages 22 and 33 years. The patients ranged in age from 7 to 66 years, and 8 of the 13 were male. All recovered. Single or paired serum specimens obtained from 4 patients and from 4 exposed but asymptomatic persons were sent to CDC for BF testing. All 4 patients and 3 of the 4 asymptomatic persons had single titers of greater than or equal to 40 and/or a 4-fold rise in titer between acute- and convalescent-phase specimens. A sample of pork from the implicated meal was examined at CDC in an artificial digestion procedure that revealed a low concentration of T. spiralis larvae.

Intensive efforts were made to educate Indochinese families in Rhode Island about the need to cook pork adequately. All state health-care providers and social service agencies were requested to emphasize this recommendation to their refugee populations. Reported by R Rotolo, MD, R Garcia, A Habib, MD, S Florio, MD, Wyckoff Heights Hospital, M Bonventre, MD, L Hair, Brooklyn Hospital, S Friedman, MD, V Skeete, MS, D Somerset, E Galaid, MPH, New York City Dept of Health, I London, MD, DL Morse, MD, R Rothenberg, MD, State Epidemiologist, New York State Dept of Health; D Lowe, MD, St. Joseph Hospital, Providence, A Werhan, A Parillo, DVM, GA Faich, MD, State Epidemiologist, Rhode Island State Dept of Health; KD Murrell, PhD, Agricultural Research Service, Animal Parasitology Research Institute, US Dept of Agriculture; Field Svcs Div, Epidemiology Program Office, Parasitic Diseases Div, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Trichinosis remains a public health problem in the United States primarily because the infection is enzootic among domestic swine. Surveillance indicates that in 75% of cases for which a probable source is identified, a pork product is incriminated as the source of infection and that ground beef--probably adulterated with pork--accounts for some of the other 25% (1-3). Since 1947, when the Public Health Service began collecting data on cases reported from all the states, the annual incidence of reported human cases has declined from 300-400 cases/year to 150. Since 1966, the annual number of reported cases appears to have stabilized at 100-150, with an average of 1 death/year (1). Factors that accounted for the decline in the number of humans infected include: 1) state laws that (although directed at preventing other diseases by prohibiting the feeding of raw garbage to swine) have reduced trichinosis in swine; 2) widespread commercial and home freezing of pork, which kills trichinae; 3)

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