Beef Jerky Gastroenteritis Outbreaks.

Abstract

In New Mexico between 1966 and 1995, eight gastroenteritis outbreaks due to ingestion of contaminated meat jerky were reported, with 250 illnesses. Primarily implicated was a locally produced jerky, came seca, made by soaking beef strips in a spicy marinade and then dehydrating them. The process uses no other preservation methods, such as salt curing or the addition of chemical preservatives. Organisms isolated from samples included Staphylococcus aureus and several types of Salmonella (thompson, cerro, montevideo, kentucky, typhimurium, and newport). The primary risk factor may be failure during processing to reach a temperature sufficient to kill these organisms (145[degrees] F for three hours). New Mexico has established guidelines that address this issue, and regulatory agencies and jerky processors need to ensure that processing brings every piece of jerky to the appropriate internal temperature.

Introduction

Dried meat, now commonly called jerky, has been a popular food for thousands of years, and was an important protein source before other methods of food storage such as refrigeration became available. For reasons of convenience and taste, jerky is still widely consumed. In New Mexico, a popular form of jerky called carne seca, is made by soaking beef strips in a spicy marinade and then dehydrating them. The process uses no other preservation methods, such as salt curing or the addition of chemical preservatives. The industry is popular and "home-grown," with products prepared in small local manufacturing operations from family recipes and marketed door to door or through local vendors. Although New Mexico has nearly 40 jerky processors, no local or state trade groups represent these in-state manufacturers.

The potential for bacterial contamination in meat and in slaughterhouses (abattoirs) is tremendous. In a study of 32 slaughterhouses, Salmonella bacteria were isolated from 21 percent of swabs taken from drains [1]. Another study found Salmonella bacteria in 40.5 percent of abattoir drains [2]. With respect to meat taken from the slaughter-houses, one of these studies found Salmonella bacteria in two percent of specimens, and yet another study found the bacteria in 12 to 18 percent of veal samples [1,3]. Among small groups of calves, Salmonella carrier rates of 50 percent are occasionally found [1].

Bacterially contaminated meat has been repeatedly linked to gastroenteritis. In the United Kingdom, 139 incidents of human infection were documented to be related to organisms found in slaughterhouses in the period of a single year [1]. In the United States, many gastroenteritis outbreaks have been linked to contamination of meat with a particularly deadly bacterium, Escherichia coli 0157:H7 [4].

Because some risk of bacterial contamination is inherent in meat, appropriate processing that reduces organism numbers is critical in preventing illness. Many processing factors are important, including handwashing, refrigeration, and prevention of cross-contamination. For 75 U.S. disease outbreaks related to food processing, however, inadequate heat processing was the factor most frequently cited--in 26.7 percent of the outbreaks [5].

Few gastroenteritis outbreaks have been linked to dried-meat products [6]. That circumstance probably can be attributed to dehydration, which is one way of destroying bacteria and safely preserving meat. Beef jerky production usually involves both desiccation and heat, and with proper controls, it achieves temperatures sufficient to kill bacteria. Dried meats and fish have, however, been implicated in botulism outbreaks and deaths [7]. Disease outbreaks also have been linked to ready-to-eat meat products such as salami and sausage [8,9].

Because of the large number of gastroenteritis cases and outbreaks related to jerky in New Mexico, the illnesses were investigated and reviewed for risk factors, and regulations were developed to curtail the problem.

Methods

By statute, cases of gastrointestinal illness must be reported to the New Mexico Department of Health (NMDOH). The New Mexico Environment Department (NMED) files written reports of all complaints. Reports of illness from two or more unrelated people possibly related to a food product receive further investigation. Depending on resources, reports from one person also receive follow-up.

Follow-up consists of inspection of the food processing or preparation premises by NMED; a search by NMDOH for more cases (case ascertainment) through contacts with medical facilities, laboratories, and those reported ill or exposed; laboratory testing provided free of charge to those with illnesses (arranged by NMDOH); laboratory testing of environmental samples such as food, water, and preparation surfaces (arranged by NMED); and possible development and administration of a questionnaire to determine risk factors (jointly developed and administered by NMDOH and NMED). Written reports of inspection, laboratory, and epidemiologic results are prepared, including an analysis of steps to prevent future problems. These reports are provided to the implicated food establishment and to other interested parties.

Results

Table 1 summarizes the jerky outbreaks reported to NMDOH and NMED. Between 1966 and 1995, eight different outbreaks of enteric illness related to consumption of jerky were identified in New Mexico, with 250 illnesses laboratory-confirmed or epidemiologically linked to contaminated jerky consumption. Seven outbreaks were traced to small New Mexico jerky processors that served areas only in the immediate vicinity of their processing plants. One outbreak was caused by antelope jerky prepared in a home for private consumption. None of the jerky was distributed to other states. The outbreaks are described in more detail below

Salmonella thompson, 1966-1967

An outbreak of confirmed Salmonella thompson infection in 97 individuals from four New Mexico counties took place between October 30, 1966, and January 20, 1967. The peak occurred during the week ending January 7, 1967 [10]. An epidemiologic investigation implicated beef jerky processed at one local company as the source of illness for 39 of the cases. Samples of the implicated beef jerky were also culture positive for S. thompson.

Staphylococcus aureus, 1982

In July 1982, 15 people became ill with S. aureus, and epidemiologic investigation found that the only food they had all eaten was beef jerky from a single processing plant. The organism was isolated from jerky samples. Investigation by NMED staff discovered that the drying temperature for the trays of meat, reported to be 100[degrees]-110[degrees] F, was insufficient to prevent bacterial growth. After the investigation, the processor stopped making beef jerky.

Salmonella cerro, 1985

In June 1985, infection with Salmonella cerro was identified in 44 people with illness onset between May 8 and July 2. All had eaten beef jerky from a single plant [11]. The organism also was isolated from jerky samples. (Six plant owners or employees and three of their children also tested positive for 5. cerro, although none of these people reported symptoms of salmonellosis.) One patient was a pregnant woman who developed amnionitis and septic shock and had to undergo an emergency cesarean section. The infant survived but was also infected with S. cerro. Six people were hospitalized because of infection.

A case control study was performed with 10 initial cases and 30 controls. Questions were asked about multiple potential sources of exposure to gastrointestinal illness, including 19 meat and dairy products, drinking water outdoor activities, eating in restaurants, and exposure to household members with diarrhea. The respondents infected with S. cerro were 9.3 times more likely to have eaten beef jerky before their illness than were the controls (95 percent confidence interval: 1.36-57.8).

Environmental inspection found that raw sliced beef was being marinated for 24 hours in a refrigerator at 38[degrees] F, a temperature insufficient to destroy bacteria. Cross-contamination may have occurred, because cleansing of the marinating vats was infrequent, and the marinade was not prechilled before being added to the sliced beef. The drying process consisted of two days in solar rooms, which at maximum efficiency reached temperatures of only 90[degrees] to 120[degrees] F. In the evenings and on days without sunshine, the jerky was held at room temperature. The program for sanitizing equipment also was ineffective.

Salmonella montevideo, 1986

On December 31, 1986, NMED received a report of five people with gastrointestinal symptoms following a family gathering the day after Christmas. Salmonella montevideo was subsequently isolated from stool samples and from beef jerky eaten by the family. The investigation identified the following problems at the processing plant: A thermometer was not routinely used to monitor temperatures, temperatures were not recorded, the radiator-type heater had no thermostat, the door to the drying room was left open, the plastic drying racks were difficult to clean and were not cleaned after every batch, and there was no sanitizer in the container that held the cleaning cloths. The maximum ambient air temperature recorded after inspection was 140[degrees] F. As the result of bad publicity from the outbreak, the processor stopped selling beef jerky.

Salmonella newport, 1987

Shortly after investigation of the previous outbreak, an additional four to seven people experienced gastrointestinal illness. Their cases appeared to be linked to Salmonella newport (Group [C.sub.2]) in jerky being sold door to door by a processor. The operation, which was illegal, was shut down, and no further investigation was conducted.

Salmonella newport, 1988

An outbreak identified in October 1988 comprised 23 laboratory-confirmed cases and 22 clinical cases of salmonellosis due to infection with S. newport. Epidemiologic investigation implicated two beef jerky processors, both of whom obtained their meat from the same packaging company. The organism was isolated from stool samples of the patients who were clinically ill, as well as in jerky samples from both processors.

All but one of the dehydrators used by the processors were manufactured for home, not commercial, use. Lids were off some dehydrators, and temperature fluctuations within each dehydrator were excessive. None of the units could heat the beef to 145[degrees] F fast enough to prevent the product from being in the danger zone for unacceptable periods of time. For instance, meat in some dehydrators remained at 80[degrees] to 90[degrees] F for up to five hours, a temperature range conducive to the growth of most enteric pathogenic bacteria.

All processors using the problematic dehydrators were required to stop production with those units until the identified deficiencies were corrected.

Salmonella sp., 1995

Between January 22 and February 11, 1995, 93 persons experienced nausea, vomiting, abdominal cramps, or diarrhea--or had a stool that tested positive for Salmonella -- after eating beef jerky from a local processor [12]. Forty of these cases were laboratory-confirmed. NMDOH's Scientific Laboratory Division isolated identical serotypes of S. montevideo, S. kentucky, and S. typhimurium from jerky and stools.

Symptoms included diarrhea (93 percent), bloody diarrhea (13 percent), abdominal cramps (87 percent), headache (74 percent), fever (61 percent), vomiting (43 percent), and chills (40 percent). People with laboratory-confirmed cases were statistically significantly more likely to experience bloody diarrhea, fever, and chills than were people with non-laboratory-confirmed cases (p [less than] .05). The duration of illness ranged from one to 40 days, with a median of seven days. Five people were hospitalized, and 40 sought medical attention.

Incubation periods ranged from zero to 14 days; the median was one day. The patients ranged in age from two to 65 years; the median was 22 years. Cases were identified in an infant and two other people who had not eaten beef jerky but had been in contact with household members or classmates who had eaten the product.

The processor reported the following preparation steps for the jerky: Frozen meat was thawed in a refrigerator and then sliced while still partially frozen. The meat was seasoned and placed on racks in a drying room. The temperature of the drying room was brought to 140[degrees] F for three hours and then held at 115[degrees] F for an additional 21 hours. Actual procedures or temperatures could not be verified. After the outbreak, Salmonella was not isolated from raw meat, flavorings, or environmental surfaces.

Staphylococcus aureus, 1995

On August 19, 1995, NMDOH received a report that a woman, her daughter, and her granddaughter had experienced severe nausea and vomiting several hours after eating homemade antelope jerky. They had had no other food in common in the previous 24 hours. A private individual who had prepared the jerky became ill after eating it, as did his mother. Thus, five people became ill after eating the antelope jerky, and there was unconfirmed information about several others. Clinical signs included nausea (100 percent), vomiting (100 percent), abdominal cramps (60 percent), nonbloody diarrhea (40 percent), fever (20 percent), and chills (40 percent). Two people saw a physician because of their symptoms and were hospitalized overnight. The duration of illness was less than one day for four of the cases; one person experienced nausea, vomiting and diarrhea for four days. The jerky was eaten on August 18 and 19, and in each case symptoms occurred the same day. One individual ate the jerky twice and became ill with vomitin g both times. The incubation period ranged from 2.5 to 13.0 hours; the median was 5.0 hours.

The jerky had been made from frozen antelope meat. A gram stain of a jerky sample showed only gram-positive cocci and low levels of Staphylococcus aureus (4,000 organisms per gram). Because insufficient sample was available, investigators could not test for the presence of Staphylococcus enterotoxin.

Regulatory Actions

In response to the outbreaks discussed above, a number of regulatory actions were taken. In 1985, the New Mexico Livestock Board developed a policy memorandum requiring that "all methods of dehydrating will have a controlled temperature of at least 140 degrees Fahrenheit." The memorandum also implemented requirements for facility, equipment, and employee hygiene and sanitation. In 1986, the New Mexico Health and Environment Department (then combined) developed an official guidance to supplement this memorandum. The guidance called for a temperature of 145[degrees] F in accordance with recommendations of the U.S. Food and Drug Administration and the Centers for Disease Control. Metal, stem-type, numerically scaled indicating thermometers, accurate to within 3[degrees] F, were required. The guidance elaborated cold-storage requirements as well as drying and sanitation requirements.

Despite enactment of these policies and guidances, however, jerky-related outbreaks continued to occur, as indicated by reports of outbreaks through 1995. Thus, in 1995, a committee of NMDOH and NMED staff was formed to evaluate the issues. This committee concluded that to ensure proper drying temperatures, an operational plan must be developed for each processing facility and for each heating unit [13].

Currently, jerky plants are inspected and permitted annually by the regional NMED environmentalist. In addition, one of four NMED food specialists inspects each plant annually to verify time, temperatures, process, and operational procedures. Record keeping and batch code information also is reviewed. Jerky plant operators are required to notify NMED of any changes they plan to make in equipment, process, recipe, species of meat, and so forth. Critical control points include ensuring that all pieces of jerky reach an internal temperature of at least 145[degrees] F within three hours so as to kill pathogenic bacteria, and then ensuring that the jerky is protected from recontamination and dried to a water activity (Aw) below 0.85. Samples are taken to the state laboratory to be tested for water activity and pH before the processors are allowed to sell.

No additional outbreaks have been documented since institution of these revised guidelines.

Discussion

Gastroenteritis from ingestion of contaminated jerky is an underreported illness. Because jerky is purchased by individuals rather than served to large gatherings, most illnesses related to its consumption probably occur sporadically and the cause probably goes unrecognized. The authors believe that the eight reported outbreaks and 250 illnesses are just the tip of the iceberg with respect to this source of food contamination.

In general, local food processors who do not sell across state lines are subject to fewer regulatory burdens than are interstate processors. The U.S. Department of Agriculture (USDA) inspects interstate processing plants for sanitation problems, although it does not have specific requirements for monitoring temperature and water activity. The New Mexico Livestock Board of the state Agriculture Department enforces USDA regulations and guidelines in other plants that sell their products wholesale. NMED thoroughly inspects jerky-manufacturing facilities before providing a permit; this inspection includes verification of the food temperature requirements. Even with regulations, however, it can be difficult to maintain periodic inspections of small geographically dispersed processors. In addition, the authors' investigations indicate that the equipment used in such operations has trouble achieving and maintaining temperatures that will control organisms. Monitoring the internal temperature of jerky pieces also is difficult.

The organisms implicated in the eight outbreaks discussed here were S. aureus and various other types of Salmonella. Because Salmonella is one of the most heat resistant of the vegetative foodborne pathogens, time and temperature guidelines developed to kill this organism should be sufficient to address most other microbiologic risks [14]. A number of other studies have documented the results of heat treatment, at various temperatures, on the viability of pathogenic organisms in meat products and eggs. In one study, no viable pathogenic organisms survived in dried sausage heated to an internal product temperature of 129[degrees] to 131[degrees] F for 3.5 hours--in contrast to product heated only to 123[degrees] to 126[degrees] F [15]. In sausage batter heated to 126[degrees] F for one hour, Salmonella typhimurium was reduced 99.99 percent, but some viable organisms remained [16].

One of the critical issues identified in these outbreaks was the difficulty of achieving the appropriate temperature, as well as of verifying that it has been reached and maintained. One pair of studies investigated the success of various thermostat settings for a meat dehydrator [17,18]. Even when the thermostat was set at 155[degrees] F air temperature in the dehydrator reached only 127[degrees] F, and viable organisms of S. aureus, Salmonella sp., Clostridium perfringens, and Bacillus subtilis remained. The internal meat temperature was not measured.

Conclusion

This investigation of the jerky-related gastroenteritis outbreaks in New Mexico indicates that the product is an underrecognized source of illness and food-related risk. Using commercial dehydrators and monitoring equipment, as well as other preservative methods, such as chemicals or salt curing, would reduce microbiological problems, but New Mexico came seca processors and customers believe that these methods would increase costs, change the nature of the product, and ruin its taste and appeal. Because of these product demands and constraints, it can be costly and time consuming for government regulators to ensure food safety Nevertheless, since 1995, the extensive beef jerky regulations developed by NMED, when vigorously enforced, have proven effective in stopping gastrointestinal outbreaks related to beef jerky products.

Acknowledgments: The authors thank the following people for their assistance in investigating the outbreaks and developing control programs for jerky processing in New Mexico: S. Castle, H. Eitzen, and M. Tanuz of the Epidemiology Office; L. Nims, P. Gutierrez, J. Miller, staff of the Scientific Laboratory Division; NMDOH field office staff; and T. Smith, J. Ajuziem, N. Weber, J. Thompson, A. Roy, K. Oldenburg, J. Sheyka, B. Briscoe, T Madrid, B. Garcia, R. Mitzelfelt, and other NMED staff

Corresponding Author: C. Mack Sewell, Dr.P.H., M.S., State Epidemiologist, New Mexico Dept. of Health.

REFERENCES

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      Jerky-Related Gastrointestinal Disease Outbreaks in New Mexico
                                                         Number Ill
   Date    Product        Organism                       (250 Total)
10/66-1/67 beef jerky     Salmonella thompson                39
   7/82    beef jerky     Staphylococcus aureus              15
5/85-7/85  beef jerky     Salmonella cerro                   44
  12/86    beef jerky     Salmonella montevideo               5
   1/87    beef jerky     Salmonella newport                  4
  10/88    beef jerky     Salmonella newport                 45
   2/95    beef jerky     Salmonella, multiple serotypes     93
   8/95    antelope jerky Staphylococcus aureus               5