During the second week of June 1985, the Scientific Laboratory Division of the New Mexico Health and Environment Department identified three isolates of an unusual serotype of Salmonella, S. cerro (group K), from residents of three counties in northern New Mexico. Only one previous human isolate of S. cerro had been reported in the state in 1985. Over the subsequent 6 weeks, 26 additional isolates were identified, all from a six-county region in north-central New Mexico. Twenty-seven (93%) of the 29 patients reported diarrheal illness. Onset of symptoms occurred between May 8 and July 2. Patients ranged in age from 0 to 58 years (median 26 years), and 17 (59%) were male. Seven of the patients were hospitalized; there were no fatalities.

A case-control study was conducted June 28 and June 29. A case was defined as a person with culture-confirmed S. cerro. Patients were excluded if another household member had reported a diarrheal illness with onset before that patient. Using a standardized questionnaire, the 10 persons meeting the case definition were interviewed for risk factors that included carne seca (beef jerky) as part of a food list. Thirty controls matched for age, sex, ethnicity, and neighborhood were also interviewed. Eight (80%) cases and nine (30%) controls reported eating carne seca during the week before onset of symptoms (p = 0.008). Two persons identified a specific brand of carne seca as the only brand eaten during the week before their illnesses. S. cerro was isolated from samples of this brand purchased from retail merchants in three cities. Salmonella was not isolated from any of the other brands tested.

The plant producing the contaminated product was inspected July

1. Preparation of the carne seca involved slicing partially thawed beef and then drying the beef in a passive solar drying room for 2-3 days. Before drying, some of the beef was marinated with a red or green chile marinade for 24 hours. The dried meat was then trimmed, weighed, and packaged on the premises. Gloves were used in processing the raw meat but not in trimming or packaging. No lot numbers were recorded on the packages. The manufacturer delivered the finished product directly to retailers. The average shelf time, based on sales records, was estimated at 1-2 weeks. Cultures of environmental surfaces were obtained at the time of the plant inspection. Thirty-four (40%) of 86 cultures were positive for S. cerro, including unprocessed, unwrapped beef, the red chile marinade, meat slicers, drying trays and racks, and packaging equipment.

Nine employees worked at the plant during the outbreak. Most usually ate the carne seca for lunch. Six of eight tested had stool cultures positive for S. cerro. In addition, stool cultures from the wife and two children of the plant owner were positive for S. cerro. All employees denied any recent diarrheal illness.

The manufacturer issued a voluntary recall of the carne seca on July 1. Fifteen of the 29 culture-confirmed cases were identified after the recall was initiated. Reported by LJ Nims, MS, PA Gutierrez, MS, LW Hughes, PhD, Scientific Laboratory Div, JM Sheyka, MS, DD Fort, Environmental Improvement Div, MV Tanuz, Health Svcs Div, SP Castle, MPH, OJ Rollag, DVM, Office of Epidemiology, HF Hull, MD, State Epidemiologist, New Mexico Health and Environment Dept; Div of Field Svcs, Epidemiology Program Office, Enteric Diseases Br, Div Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: S. cerro is a rare but widely distributed serotype in the United States, and represented less than 1% of the 35,862 human isolates reported to CDC in 1984. From 1968 to 1984, only four human isolates were reported in New Mexico.

Carne seca is a popular snack food prepared from sliced raw meat or fish that has been salted, seasoned, and dried. This is the third outbreak in New Mexico in which contaminated carne seca was identified as the vehicle for foodborne illness. In December 1966, 41 persons were infected with S. thompson related to contaminated, locally produced carne seca (1). In July 1982, four persons became ill with staphylococcal food poisoning after eating another locally produced carne seca (2).

Carne seca is generally considered a shelf-stable food because desiccation decreases the available water content limiting microbial growth (3). However, data evaluating the safety of carne seca preparation are limited (4-6). In this outbreak, the passive solar system used by the manufacturer to dry the carne seca was uncontrolled and investigation showed that it failed to maintain temperatures high enough to inhibit the growth of Salmonella. Successive batches of carne seca probably became contaminated through contact with contaminated equipment, red chile marinade, and drying racks. Salmonella was probably introduced into the plant about the first week of May, but its origin is unknown. Further replication was unlikely to have occurred after the drying process was complete.

This outbreak was recognized primarily because it involved an unusual serotype of Salmonella. Because there were no other obvious common links between affected individuals, an outbreak caused by a more common serotype could have gone unrecognized. In 1983, 66 isolates of S. cerro from nonhuman sources were reported to CDC and the U.S. Department of Agriculture. The two most common sources were bovine sources (21%) and animal feeds and protein supplements (20%) (7). Carne seca-associated outbreaks may be more common than formerly appreciated. Further efforts are necessary to establish guidelines for its safe production.

References

1. New Mexico Department of Public Health. Unpublished data, 1966.

2. Lapham SC. New Mexico Health and Environment Department. Unpublished data, 1982.

3. Banwart GJ. Basic food microbiology. Westport, Connecticut: AVI Publishing Co. Inc, 1979:125, 160.

4. Holley RA. Beef jerky: viability of food-poisoning microorganisms on jerky during its manufacture and storage. Journal of Food Protection 1985;48:100-6.

5. Delong D. How to dry foods. Tuscon, Arizona: HP Books, Inc., 1979:79-82, 150-5.

6. Holley RA. Beef jerky: fate of Staphylococcus aureus in marinated and corned beef during jerky manufacture and 2.5O C storage. Journal of Food Protection 1985;48:107-11.

7. CDC. Salmonella surveillance report, 1984.

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