On Sept. 18, 2006, the California Department of Public Health (CDPH) was notified of two children hospitalized with hemo-lytic uremic syndrome (HUS). One of the patients had culture-confirmed Escherichia coli O157:H7 infection, and both patients had consumed raw (unpasteurized) cow milk in the week before illness onset. Four additional cases of E. coli O157:H7 infection in children who had consumed raw cow’s milk or raw cow’s colostrum produced by the same dairy were identified during the following three weeks. In California, intrastate sale of raw milk and raw colostrum is legal and regulated.
As a result of this and other outbreaks, California enacted legislation (AB 1735), which took effect Jan. 1, 2008, setting a limit of 10 coliforms/mL for raw milk sold to consumers. Raw milk in several forms, including colostrum, remains a vehicle of serious enteric infections, even if the sale of raw milk is regulated.
In mid-September 2006, the parent of one of the two children hospitalized with HUS notified California Department of Food and Agriculture (CDFA) that both children had consumed raw skim milk from dairy A in the days before illness onset. Dairy A, a licensed raw milk dairy, sells raw milk, raw cream, raw butter, raw cheese, raw colostrum, and kefir throughout California at retail stores and nationwide via Internet sales, all under a single brand (brand A).
On September 21, 2006, CDFA issued a recall and quarantine order for all raw milk, raw cream, and raw colostrum produced by dairy A. The order was extended on Sept. 22 to include all raw products from dairy A, except for cheeses aged at least 60 days according to California and Food and Drug Administration (FDA) standards (the 60-day curing process has historically been considered sufficient to eliminate or reduce pathogens that were in the milk; however, its efficacy has been questioned, and FDA is reviewing the safety of raw milk cheeses). Dairy A also was placed under a separate restriction by CDFA during Sept. 21–29 that prevented it from bottling fluid milk and cream because of persistent high standard plate counts.
The 61 health jurisdictions in California were notified on Sept. 20, 2006, to be alert for cases of E. coli O157:H7 and other Shiga toxin-producing E. coli associated with consumption of raw milk. Six cases were identified; four persons had culture-confirmed infections, one had a culture-confirmed infection and HUS, and one had HUS only. The median age of patients was 8 years. The six cases were geographically dispersed throughout California. All six patients reported bloody diarrhea; three were hospitalized. Illness onset occurred during Sept. 6–24, 2006.
Five patients reported they had consumed brand A raw dairy products in the week before their illness onset; the sixth patient denied drinking brand A raw milk, although his family routinely purchased it. Two of the patients consumed raw whole milk, two consumed raw skim milk, and one consumed raw chocolate-flavored colo-strum. Four of the five patients routinely drank raw milk from dairy A. One patient was exposed to brand A dairy product only once; he was served raw chocolate colostrum as a snack when visiting a friend. No other food item was commonly consumed by all six patients. No other illness was reported among household members who consumed brand A dairy products.
Investigators determined that the patients consumed raw milk from lots produced at dairy A during Sept. 3–13, 2006. Milk samples from these production dates were not available for testing. Fifty-six product samples from several lots with code dates of Sept. 17, 2006, or later were retrieved from retails stores and dairy A and were tested for aerobic microflora, total coliform, fecal coliform, and E. coli O157:H7. The outbreak strain of E. coli O157:H7 was not found in any product samples. However, standard aerobic plate counts and coliform counts of collected samples with code dates of Sept. 17 through Oct. 9, 2006, were indicative of contamination. Colostrum samples had high standard plate counts and total coliform counts, and fecal coliform counts of 210–46,000 MPN/g. California standards limit standard plate counts for raw and pasteurized milk to 15,000 CFU/mL and total coliform counts for pasteurized milk to 10 coliform bacteria/mL. At the time of this outbreak, California did not have a coliform standard for milk sold raw to consumers. California also classifies colostrum as a dietary supplement, for which it has no microbiologic standards, rather than a milk product.
CDFA and CDPH conducted an initial inspection and environmental investigation of the milk plant and dairy on Sept. 26. E. coli O157:H7 was not isolated from any of four environmental samples. Samples from three heifers yielded E. coli O157:H7, but the isolates differed from the outbreak pattern.
Morbidity and Mortality Weekly Report editorial note: Raw cow milk and raw milk products have been implicated in the transmission of multiple bacterial pathogens, including Campylobacter spp., Brucella, Listeria monocytogenes, Salmonella spp., and E. coli. In a recent review of E. coli O157 infections, raw milk products accounted for 4% of outbreaks during a 20-year period. E. coli O157:H7 is responsible for an estimated 73,000 cases of illness annually, and serious sequelae, including HUS and death. Children, older adults, and persons with low levels of gastric acid are particularly vulnerable.
Raw milk products tested from dairy A were not produced during the same time as the products consumed by the patients in this outbreak. Although the outbreak strain of E. coli O157 was not isolated from dairy A products, the tested products did have high standard plate counts, many exceeding California standards for raw milk, and total coliform counts that exceeded California standards for pasteurized milk. Non-outbreak strains of E. coli O157 also were isolated from samples from dairy A cows, indicating shedding of this pathogen in the herd. Raw milk from dairy A was the likely vehicle of transmission, but the exact mode of milk contamination in this outbreak was not determined. Asymptomatic cows can harbor pathogens and cause human illness by shedding pathogens in untreated milk or milk products. These findings suggest that if raw milk had been subject to the same coliform standard as pasteurized milk in California, milk from dairy A might have been excluded from sale and this outbreak might have been averted.
FDA mandates that all milk and milk products for direct human consumption be pasteurized in final package form if they are to be shipped for interstate sale. Currently, 21 states require pasteurization of all milk products for sale. However, 25 states, including California, allow raw milk to be sold in some form to the public. Those states that permit the sale and consumption of raw milk report more outbreaks of foodborne disease attributed to raw milk than those states that have stricter regulations. During 1973–1992, raw milk was implicated in 46 reported outbreaks. Nearly 90% of these outbreaks (40 out of 46) occurred in states that allow the sale of raw milk, suggesting that even the regulated sale of raw milk might not be adequate to prevent associated illnesses.
This is the first outbreak reported to CDC in which colostrum has been implicated as a form of raw milk consumed by any patients in a raw milk-associated outbreak. Colostrum is purported to have increased concentrations of nutrients/antibodies and is marketed as a dietary supplement in California and is regulated by the CDPH Food and Drug Branch. The colostrum products tested in this investigation were nearly as contaminated as other forms of raw milk tested; therefore, in this outbreak, the risk for human illness from consuming either product was probably similar. Exemption of colostrum from state dairy regulations is not supported by the findings in this outbreak investigation.
From 1998 to 2005, raw milk or raw milk products have been implicated in 45 foodborne illness outbreaks in the United States, accounting for more than 1,000 cases of illness. Additional efforts are needed to educate consumers and dairy farmers about illnesses associated with raw milk and raw colostrum. To reduce the risk for E. coli O157 and other infections, consumers should not drink raw milk or raw milk products.
This information excerpted from the Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report, July 13, 2008. For the full report and references, visit www.cdc.gov/mmwr.