Group C Streptococcal Infections Associated with Eating Homemade Cheese -- New Mexico

Between July 25 and September 9, 1983, 16 cases of invasive group C streptococcal infection were identified in northern New Mexico. The group C streptococcus was isolated from the blood of 15 patients and the pericardial fluid of one patient. The organism isolated from 14 of the patients has been identified as a group C B-hemolytic streptococcus--species Streptococcus zooepidemicus; the species of the remaining two isolates have not yet been determined. Ages of the 16 patients ranged from 19 to 89 years (median 74); 10 were male. All patients were Hispanic.

In general, the clinical syndrome was characterized by fever, of the patients has been identified as a group C B-hemolytic streptococcus--species Streptococcus zooepidemicus; the species of the remaining two isolates have not yet been determined. Ages of the 16 patients ranged from 19 to 89 years (median 74); 10 were male. All patients were Hispanic.

In general, the clinical syndrome was characterized by fever, chills, and vague constitutional symptoms. However, five patients had localized signs of infection, including pneumonia, endocarditis and meningitis, pericarditis, and abdominal pain that led to a cholecystectomy for one patient and an appendectomy for another patient. Two patients with multiple underlying medical problems died.

A case-control study was undertaken to identify possible risk factors for contracting group C streptococcal infections. Patients and controls were matched for age, sex, ethnicity, and neighborhood of residence. Some of the possible risk factors investigated included underlying illnesses, immunosuppressive medications, animal exposure, group activities, restaurants visited, and food items consumed. Initial questionnaires identified eating "queso blanco," a homemade white cheese, as the only risk factor associated with illness (10 of 15 case patients versus 7 of 45 controls, p 0.001). During subsequent discussions, four of the five patients who did not report in the case-control study that they had eaten the homemade cheese later remembered that they had consumed the cheese before the onset of illness. Thus, only one patient did not recall having eaten the cheese before becoming ill.

The sole source of the homemade cheese consumed by the patients was an ungraded, small (seven cows), family dairy farm in northern New Mexico. At the farm, the cheese was made from raw cows' milk and was not subsequently aged. It was distributed to several stores in northern New Mexico within 24-48 hours after preparation in the family kitchen. Milk samples from the cows and cheese samples from the stores were obtained for microbiologic analysis. Group C B-hemolytic streptococci, species S. zooepidemicus, have been isolated from multiple samples of each.

Public health control measures included closing the dairy operation, removing the cheese from the stores, and advising the public to dispose of any "queso blanco" purchased from the stores that sold the implicated product. No new cases of group C streptococcal infections have been identified since these interventions were implemented. Reported by FH Espinosa, MD, WM Ryan, MD, PL Vigil, MD, Espanola Hospital, Espanola, DF Gregory, MD, RB Hilley, MD, DA Romig, MD, RB Stamm, MD, ED Suhre, MD, PS Taulbee, MD, LH Zucal, MD, St. Vincent Hospital, Santa Fe, RW Honsinger Jr, MD, PJ Lindberg, MD, Los Alamos Medical Center, Los Alamos, M Barcheck, JA Miller, R Mitzelfelt, JM Montes, LJ Nims, OJ Rollag, DVM, State Public Health Veterinarian, N Weber, JM Mann, MD, State Epidemiologist, New Mexico Health & Environment Dept; Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Group C streptococci are a common cause of infection in several animal species but are generally considered to be a rare cause of infection in humans (1). Of the four species of group C streptococci, S. equisimilis has been reported to cause most human illnesses, including bacteremia, endocarditis, meningitis, pneumonia, epiglottitis, puerperal sepsis, and wound infections. However, S. zooepidemicus has been associated with two outbreaks of pharyngitis and nephritis in Europe (2,3). While pharyngitis was not a part of the clinical syndrome in the outbreak reported here, it is too early to tell if poststreptococcal glomerulonephritis will develop.

In both of the European outbreaks, unpasteurized milk was suspected as the source of infection. The outbreak reported here is the first epidemic of group C streptococcal infections in the United States and is the first such reported outbreak in which the vehicle--cheese made from unpasteurized cows' milk--has been epidemiologically implicated. Although S. zooepidemicus and S. equisimilis are rarely reported causes of mastitis in cows, the cause of this outbreak was contaminated milk from cows with mammary infections due to S. zooepidemicus.

Because few laboratories routinely determine the species of group C streptococci, the number of human infections due to S. zooepidemicus is not known. Furthermore, group C streptococci may be mistakenly identified as group A strains if only bacitracin susceptibility testing is done to differentiate group A streptococci from other B-hemolytic streptococci. It is impractical for clinical laboratories to routinely determine the serogroup and species of all B-hemolytic streptococci isolated from all sites. However, serogroups of B-hemolytic streptococci and species of group C strains isolated from blood and other normally sterile sites should be identified if further information is to be gained about the epidemiology of such infections.

References

1. Ghoneim AT, Cooke EM. Serious infection caused by group C streptococci. J Clin Pathol 1980;33:188-90.

2. Duca E, Teodorovici G, Radu C, et al. A new nephritogenic streptococcus. J Hyg, Camb. 1969;67:691-8.

3. Barnham M, Thornton TJ, Lange K. Nephritis caused by Streptococcus zooepidemicus (Lancefield group C). Lancet 1983; 8331:945-8.

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