A common-source outbreak of trichinosis from consumption of bear meat. (Features).

Introduction

Trichinosis is a parasitic disease caused by a nematode of the genus Trichinella, an intestinal roundworm. In addition to T. spiralis, most commonly associated with domestic pork, four other species of Trichinella are now recognized, including T. nativa in arctic bears (Centers for Disease Control and Prevention [CDC], 2001a). Illness occurs after ingestion of meat that contains ericysted larvae (trichinae). Stomach acids dissolve the protein cysts, releasing the larvae. The larvae pass to the small intestine, mature into adult worms, and reproduce. The trichinae then migrate to and eventually become encapsulated in the muscles. Systemic signs and symptoms usually appear eight to 15 days after ingestion of infected meat, but the time varies between five and 45 days, depending on the number of trichinae ingested. Sudden appearance of muscle soreness and pain, together with edema of the upper eyelids, is a characteristic sign. Thirst, profuse sweating, chills, weakness, prostration, and rapidly increasing eosin ophilia may follow shortly after the ocular signs. Gastrointestinal symptoms, such as diarrhea, due to intraintestinal activity of the adult worms, may precede the ocular manifestations. Remittent fever is usual, sometimes as high as 104[degrees]F; the fever terminates after one to six weeks (Chin, 2000).

On September 12, 1998, a 61-year-old male ate two bear burgers that had been cooked rare in a microwave oven. This individual had a history of eating wild game. On September 26, he became ill, experiencing cramps, diarrhea, nausea, headache, body aches, chills, sweating, fever (105[degrees]F), muscle aches and weakness, and swelling of the eyelids. He sought treatment from his family physician. Blood tests indicated leukocytosis and eosinophilia (20 percent). A muscle biopsy demonstrated trichinae cysts.

The meat came from two bears hunted in Ontario, Canada, in June 1998. Both bears had been field-dressed, quartered, and divided between two hunters and placed in coolers for refrigeration and transport back to the United States.

Cuts of meats from the bears were commingled by the hunters when the meat was placed in the coolers. The meat was then processed into ground meat and roasts by a local meat processor in Montgomery County, Ohio, in July 1998, taken home by the hunters, and stored in home freezers.

On October 13, 1998, 22 male members of a local church attended a supper, where 15 of them consumed bear meat served as patties. The patties were hand-formed and prepared from bulk ground meat by two of the church members and cooked to order on a grill. This meat was from the hunt described above, which was the same source of meat consumed by the person who had the index case.

Methods

The health district first received reports of illness on November 9 from a local physician who examined a number of patients on November 7 and 8 in the emergency room at a local hospital. All had attended the church supper on October 13. As of November 8, four were symptomatic. In addition, four asymptomatic attendees of the church supper sought treatment because of their consumption of the bear meat. Three more symptomatic patients sought treatment during the following week. Blood tests revealed elevated levels of eosinophils in five of the seven cases (71 percent). Eosinophilia levels among these cases were 17 to 42 percent, a range consistent with parasitic infection. Blood tests also were ordered for the asymptomatic group, with eosinophil levels falling within the normal range (1 to 3 percent).

Initial interviews were conducted with several of the patients. A list of attendees of the church supper and a list of food items served were obtained. During these initial interviews, it was discovered that the bear meat had been freely distributed to several households. Both ground meat and bear roasts had been given out. From these households, 13 more people had eaten the bear meat.

One recipient of the meat operated a daycare center out of her home in Hamilton (Butler County), Ohio. She had prepared a spaghetti sauce using the ground bear meat as an ingredient and had served the spaghetti to the daycare children. It appeared that the sauce had simmered at length and probably reached cooking temperatures sufficient to destroy any organism as there were no reports of illness in this group.

The recipients of the bear meat in the second household reported that they had cooked meat patties well-done on a grill. The recipient in the third household reported that he had cooked a bear roast well-done as well. Neither household reported illness.

A sample of the bear meat was obtained for laboratory examination and sent to CDC on November 12. CDC identified Trichinella (25 larvae per 10 grams) in the sample. Larval specimens were sent to the Trichinellosis Reference Centre in Rome, Italy, for positive identification, where the larvae were determined to be Trichinella T6. Trichina infection was therefore established both from muscle biopsy in the index case and through direct examination of the bear meat by CDC. It was estimated that 260 pounds of bear meat was processed from the two bears and divided between the two hunters. Therefore, a top priority was to determine the distribution and disposition of the remaining bear meat to prevent further human exposure and to prevent the introduction of the trichinae into wildlife populations.

Distribution of Bear Meat

Hunter No. I (100 Pounds of Meat)

About 25 pounds of meat had been given to a friend, who was subsequently instructed not to eat the meat. Attempts to recover this meat for proper disposal were unsuccessful.

About 25 pounds had been given to an employee of the hunter, who, when contacted, stated that all the meat had been consumed by household members. There were no reports of illness among this group, according to the employee.

The health district was able to collect the remainder of the meat, which was incinerated at the animal shelter.

Hunter No. 2 (160 Pounds of Meat)

About 25 pounds of meat had been given to a friend. The health district contacted the friend, who said that he had had the bear meat disposed of in a sanitary landfill after learning of the associated illnesses. Hunter No. 2 said that he had consumed some of the meat and that the remainder had been consumed at the church supper.

A questionnaire was developed by the Ohio Department of Health for interviewing the attendees of the church dinner and any others who may have consumed bear meat. Interviews were conducted by health district staff. Information was gathered on symptoms, duration of illness, thoroughness of cooking, quantity consumed, and food consumption histories, with special attention given to any pork or wild game consumption. This information was entered into an Epi Info Version 6.04 (Dean, Dean, Burton, & Dicker, 1997) database and analyzed.

Results

Completed questionnaires were obtained from the person with the index case, 22 attendees from the church supper, 10 people associated with the daycare center, and three people from two other households who had received the bear meat--that is, from a total of 36 individuals.

A confirmed case of trichinosis is defined as an illness clinically compatible with trichinosis combined either with demonstration of Trichinella larvae in a muscle biopsy or with a positive serologic test for Trichinella. After one person is found to have a confirmed case, all associated cases are considered confirmed if the people involved shared an epidemiologically implicated meat product and have a clinically compatible illness (CDC, 1997).

Twenty-two people attended the church supper. Of the 15 attendees who ate the bear meat, seven became ill (attack rate = 46.7 percent) (Table 2). Having eaten bear meat at the church supper was associated with increased risk of illness (p = .05). The remaining seven people who also attended the supper did not eat the bear meat and did not become ill. The 13 other people who did not attend the supper but who ate the bear meat reported no illness. A total of eight people, including the person with the index case, had illnesses that met the case definition for trichinosis.

The median incubation period from time of the meal was 21 days, with a range from 11 to 30 days. All cases occurred in males; the median age was 37 years, with a range of 26 to 55 years.

Of the seven symptomatic attendees of the church supper, all had eaten the epidemiologically implicated bear meat at the church supper. One attendee had a positive serologic test for trichinosis. All seven reported nausea, sweating, and body aches, and all had at least five of the following additional symptoms: diarrhea (six), muscle aches (six), muscle weakness (six), chills (six), fever (five), cramps (five), headache (five), abdominal pain (five), rash (five), and swelling of the eyelids or around the eye (five) (Table 1). Blood tests revealed elevated levels of eosinophils in five of the seven cases (71 percent). The range of eosinophilia among these cases was 17-42 percent. All seven attendees therefore had illnesses that met the CDC case definition for trichinosis (CDC, 1997).

As part of the interview, an attempt was made to identify how thoroughly the bear meat had been cooked, because adequate cooking destroys the organism. Questions describing the cooked bear meat as having been served rare, medium, or well-done were asked of the people who had eaten the bear meat. Well-done was defined as no pink inside and no visible blood; medium as pink inside with slight blood; and rare as pink to red inside with considerable blood. Only the person with the index case stated that the meat was cooked rare. Of the church dinner attendees, seven became ill after eating meat they described as medium or well-done. The other eight people who ate bear burgers at the church dinner and did not become ill described the meat as well-done. Ill people who believed they had eaten medium or well-done burgers most likely ate meat cooked at internal temperatures insufficient to destroy the trichinae. Thirteen others who had eaten the bear meat did not become ill. Two had eaten the meat as well-done burgers , one had eaten it as a well-done roast, and 10 had eaten it in spaghetti sauce.

An attempt also was made to quantify the amount of bear meat consumed, because development of illness and severity of illness are dose-dependent. An association between development or severity of illness and the amount of bear burger consumed could not, however, be determined. Four of the eight people with cases of trichinosis consumed two burgers each (including the person with the index case), while the remaining four ate one burger each.

Discussion and Conclusions

Trichinella species are found in virtually all warm-blooded animals. Since 1947, when trichinosis was designated a reportable disease, the number of cases reported annually has declined from an average of 400 cases per year in the late 1940s (CDC, 1991) to fewer than 50 cases per year since 1993 (CDC, 2001b). Cases of trichinosis have continued to decline, with 13 cases of trichinosis reported in the United States for 1997, 19 cases reported for 1998, and 12 cases reported for 1999 (CDC, 2001b).

The proportion of cases associated with eating contaminated commercial pork has been declining since 1975 (CDC, 1991). As commercial pork has become a less frequent source of infection, the percentage of annual cases due to eating wild animal meat has increased (Bailey & Schantz, 1988). In 1985, Trichinella-infected meat was obtained through hunting in 20 of the 41 cases (49 percent) reported for which the meat source could be identified (Bailey & Schantz, 1987). Of these 20, the most common game animal was bear (15 cases). In 1986, wild game was implicated in 74.4 percent of cases for which a source was reported (Bailey, & Schantz, 1988).

Consumption of meat from any carnivorous animal that has fed on trichina-infected flesh poses a risk, and all wild animal meat must be assumed to be infected with trichinae (Bailey & Schantz, 1988). Hunters should be educated to consider the possibility of infection as they prepare and consume game. To ensure that Trichinella are destroyed, meat should be thoroughly cooked to an internal temperature of 170[degrees]F throughout. Cooking in a microwave oven can result in variability of internal temperatures in the meat, and proper inactivation of the disease-producing organism may not occur (Zimmerman, 1984). In the outbreak discussed here, the person with the index case had knowingly eaten bear meat that was undercooked in a microwave oven. The people with the remaining cases ate bear burger that was apparently not sufficiently cooked to kill trichinae.

It is also important for hunters to know that freezing is not a reliable method of inactivating trichinae. Trichinella spiralis, the classic agent of trichinosis, is inactivated by freezing cuts of meat up to 6 inches (15 cm) thick at 5[degrees]F (-15[degrees] C) for 30 days or at -13[degrees]F (-25[degrees]C) for 10 days; it is inactivated in cuts of meat greater than 6 inches thick at -13[degrees]F (-25[degrees]C) for 20 days (Chin, 2000). The cold-resistant arctic strains Trichinella T6 and Trichinella nativa, however, are not killed at these times and temperatures (CDC, 1996; Chin, 2000). According to information obtained in this investigation, the bear meat associated with the Montgomery County, Ohio, outbreak had been frozen for at least 60 days. The home freezer temperatures were unknown, however, so it was not possible to compare those temperatures to the temperatures established for T. spirails.

Physicians should be aware of the continued presence of Trichinella sp. in commercial pork and wild game and should consider a trichinosis diagnosis for any patient who has a compatible illness and dietary preferences that pose a risk for infection (CDC, 1996). In the outbreak reported here, an alert physician diagnosed trichinosis, established the common source of infection, and promptly reported the case to the health district.

TABLE 1

Symptoms Among Attendees of Church Supper Who Became III (N = 7)

Symptom                 Number  Percentage

Nausea                    7       100.0
Sweating                  7       100.0
Body aches                7       100.0
Diarrhea                  6        85.7
Muscle aches              6        85.7
Muscle weakness           6        85.7
Chills                    6        85.7
Cramps                    5        71.4
Headache                  5        71.4
Abdominal pain            5        71.4
Rash                      5        71.4
Swelling of eyelids or    5        71.4
area around the eye
Fever                     5        71.4
Muscle swelling           3        42.9
Vomiting                  2        28.6

TABLE 2

Food-Specific Attack Rates for Those Who Ate at Church Dinner (N = 15)

                              Ate Food                  Did Not Eat Food

Food            Cases     Total     Attack Rate(%)  Cases     Total

Bear meat         7        15             47          0         7
Beef hamburger    0         2              0          7        17
Potato salad      3        12             25          3         8
Baked beans       3        13             23          2         7
Dessert           5        15             33          0         4

                Did Not Eat Food

Food            Attack Rate(%)  p Value (a)

Bear meat              0           0.05
Beef hamburger        41             NS (b)
Potato salad          38             NS
Baked beans           29             NS
Dessert                0             NS

(a)Fisher's exact test, two-tailed.

(b)Not significant.

Acknowledgements: The authors wish to recognize the following individuals for their assistance in this investigation: Monte Gardner, R.S., J. Michael Phillips, M.S.E.H., R.S., Phillip Lutton, S.I.T., Jenny Dillon, R.N., Molly Cassino, R.N., Glenda Hubbard, M.P.H., and Marilyn Sitaker, M.P.H. of the Combined Health District of Montgomery County; Ellen Salehi, M.S., and Kathleen Smith, D.V.M., MPH., of the Bureau of Infectious Disease Control, Ohio Department of Health; and Peter M. Schantz, V.M.D., Ph.D., and Vance Dietz, M.D., M.P.H. & T.M., of the Division of Parasitic Diseases, CDC.

REFERENCES

Bailey, TM., & Schantz, P.M. (1987). Trichinosis surveillance, 1985. CDC surveillance summaries. Morbidity and Mortality Weekly Report, 36(SS-2), 1-5.

Bailey, T.M., & Schantz, P.M. (1988). Trichinosis surveillance, United States, 1986. Morbidity and Mortality Weekly Report, 37(SS-5), 1-8.

Centers for Disease Control and Prevention. (1991). Trichinella spirails infection--United States, 1990. Morbidity and Mortality Weekly Report, 40(4), 57-60.

Centers for Disease Control and Prevention. (1996). Outbreak of trichinellosis associated with eating cougar jerky-Idaho, 1995. Morbidity and Mortality Weekly Report, 45(10), 205-206.

Centers for Disease Control and Prevention. (1997). Case definitions for infectious conditions under public health surveillance. Morbidity and Mortality Weekly Report, 46(RR-10), 40.

Centers for Disease Control and Prevention. (2001a). Trichinellosis. http://www.dpd.cdc.gov/dpdx/HTML/Frames/S-zrrichinellosis/body_Trichi nellosis_pagel.htm (18 Sept. 2001).

Centers for Disease Control and Prevention. (2001b). Summary of notifiable diseases, United States 1999. Morbidity and Mortality Weekly Report, 48(53), 75, 85.

Chin, J. (Ed.). (2000). Trichinellosis (Trichiniasis, Trichinosis), In Control of communicable diseases manual (17th ed., pp. 508-511). Washington, DC: American Public Health Association.

Dean, A.G., Dean, A.J., Burton, A.H., & Dicker, R.C. (1997). Epi info 6 version 6.04b. A word processing, database and statistics program for public health. Stone Mountain, GA: USD, Inc.

Zimmerman, W.J. (1984). Power and cooking time relationships for devitalization of trichinae in pork roasts cooked in microwave ovens. Journal of Food Science, 49, 824-826

RELATED ARTICLE: Did you know

The groups most vulnerable to foodborne illnesses--the very young, the elderly and pregnant women--constitute 2025% of the overall population and are the most rapidly expanding segments of the US population.

Source: The Food Safety Professional

Corresponding Author: Morton Nelson, M.D., MPH., Medical Director, Combined Health District of Montgomery County, Ohio, and Professor of Community Health, Wright State University School of Medicine, Reibold Bldg., 117 S. Main St., Dayton, OH 45422-1280. E-mail: [e-mail].