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Epidemiologic Notes and Reports Trichinosis -- Texas

On April 3, 1984, a private physician reported four cases of trichinosis among Laotians living in Amarillo, Texas, to the Bureau of Epidemiology, Texas Department of Health. The four patients were members of three households and had onset of illness between February 21 and March 12. Because of the large Laotian population resettled in this area and its previously noted practice of inadequately cooking pork (1), an investigation was begun to determine the extent of the outbreak. A survey, seeking a history of symptoms commonly seen with trichinosis (fever, muscle pain, periorbital edema, and malaise), was undertaken in households of known patients and their Laotian neighbors. If symptoms of trichinosis were present, serum was obtained for serodiagnosis.

During the investigation, five additional cases of trichinosis were found. Three persons with possible trichinosis were also identified but had moved to California to an unknown address and could not be contacted. All nine patients were Laotian, living in four unrelated households. All reported consuming pork purchased at a small local pig farm. Incubation periods for six patients ranged from 4 days to 2 weeks; for three who frequently consumed pork from the implicated farm, they were indeterminable. All patients were asymptomatic when interviewed but reported having the following symptoms: fever (all nine persons (100%)), muscle pain (six (67%)), malaise (six (67%)), periorbital edema (five (56%)), vomiting (two (22%)), and diarrhea (two (22%)). One person was pregnant. Laboratory studies of those seen by a physician during acute illness revealed eosinophilia and elevated creatine kinase. Five of the six patients tested for antibody to Trichinella sp. with the bentonite flocculation test had titers of 1:10 or greater, compatible with recent infection, and the remaining patient had a titer of 1:5. No patients had previous serologic testing to demonstrate seroconversion. A muscle biopsy performed on one patient was negative for Trichinella sp. but had areas of slight basophilic degenerative changes with focal eosinophilic infiltration. Of the five patients treated during acute disease, three received prednisone and thiabendazole; one, prednisone only; and one, thiabendazole only. The patient treated with thiabendazole developed pruritis after 2 days of therapy, but it disappeared when the drug was discontinued.

Investigation by the Texas Department of Health revealed that the pigs on the farm were occasionally fed untreated restaurant refuse; in addition, the animals wandered freely, allowing potential contact with rodent and other animal carcasses. The Texas Animal Health Commission inspected the farm but saw no evidence that garbage was being fed to the pigs at the time. The farm had previously been implicated as the source of a Trichinella sp. infection in 1981.

No further cases have been reported. None of the patients developed complications; the outcome of the pregnancy is unknown. Serum from pigs at the implicated farm is being sent to the U.S. Department of Agriculture to test for trichinosis antibody. In an effort to educate the Laotian population, the Texas Department of Health is developing a pamphlet on trichinosis and its prevention written in Laotian. Reported by C Reed, MPH, J Norred, H Moritz, MD, Public Health Region 1, CE Alexander, MD, State Epidemiologist, Texas Dept of Health; Div of Parasitic Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Trichinella spiralis, first noted to be pathogenic for humans in 1859 (2), remains a public health problem in the United States. Infection occurs when raw or inadequately cooked meat, most commonly pork, is ingested. Of cases reported during 1975-1981, where an infected meat item was identified, pork was implicated in 79.1%; wild meat, in 13.9%; and ground beef, in 7.0%. The incriminated ground beef was believed to have been adulterated by pork products (3).

Commercially or privately slaughtered pigs are not inspected for trichinae in the United States (4). Nevertheless, the reported incidence of trichinosis has declined in the United States from 300 to 400 cases annually in the late 1940s to about 100-150 cases per year (3). This can be attributed, in part, to: (1) state and federal laws that prohibit feeding untreated garbage to swine (5); (2) consumer awareness of the need to cook pork products adequately; and (3) the widespread practice of freezing pork, which kills trichinae (6). An estimated one million garbage-fed swine reach the market annually (4); law enforcement concerning feeding untreated garbage to swine varies from state to state. Moreover, it has been shown that swine readily feed on barnyard rodents that may harbor Trichinella sp. and may thus become infected (6). Consequently, trichinosis control depends almost entirely on the way consumers store and prepare pork.

Groups whose food preferences include raw or inadequately cooked pork have a higher risk of trichinosis (3). This is reflected in the ethnic-related prevalance of trichinosis. In an autopsy survey, the prevalence of infection among German and Italian immigrants in the United States was nearly twice the national rate (28.3%, 29.7%, and 16.1%, respectively) (7). Recent reports of trichinosis outbreaks (2) involve groups, especially such recent immigrants as Southeast Asian refugees, who do not treat, freeze, or thoroughly cook American pork. To help prevent future outbreaks, special health-education programs may be necessary for these new consumers.


  1. CDC. Common-source outbreaks of trichinosis--New York City, Rhode Island. MMWR 1982;31:161-4.

  2. Campbell WC. Historical introduction. In: Campbell WC, ed. Trichinella and trichinosis. New York: Plenum Press, 1983:1-30.

  3. Schantz PM. Trichinosis in the United States--1947-1981. Food Technology 1983;March:83-6.

  4. Leighty JC. Public-health aspects (with special reference to the United States). In: Campbell WC, ed. Trichinella and trichinosis. New York: Plenum Press, 1983:501-13.

  5. Juranek DD, Schultz MG. Trichinellosis in humans in the United States: epidemiologic trends. In: Kim CW, Pawlowski ZS. Trichinellosis. Hanover, New Hampshire: University Press of New England, 1978:523-8.

  6. Murrell KD, Gamble HR, Schad GA. Experimental transmission of Trichinella spiralis to swine by infected fats. Proc. Helminthol. Soc. Wash. 1984;51:66-8.

  7. Wright WH, Jacobs L, Walton AC. Studies on trichinosis. XVI. Epidemiological considerations based on the examination for trichinae of 5,313 diaphragms from 189 hospitals in 37 states and the District of Columbia. Public Health Rep 1944;59:669-81.

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