Volume 28-01
1 January 2002

[Table of Contents]

ESCHERICHIA COLI O157 OUTBREAK ASSOCIATED WITH THE INGESTION OF UNPASTEURIZED GOAT'S MILK IN BRITISH COLUMBIA, 2001

Public health inspectors from the Central Vancouver Island Health Region (CVIHR) investigated an outbreak of Escherichia coli O157:H7 in August 2001. The source of the implicated goat's milk in this outbreak was from a co-operative farm south of Nanaimo, on Vancouver Island, British Columbia (B.C.). Nubian goats were co-owned by 18 families at the time of the outbreak. The product label on the distributed milk read as follows: "milked under the strictest sanitary conditions. If pasteurization is desired, heat at 72.8E C for 30 seconds then refrigerate". Unpasteurized milk from this facility had been distributed to participating families for approximately 10 years.

E. coli O157:H7 was first isolated from a 1 year old child in a stool specimen submitted to the Nanaimo Hospital on 14 August, 2001. Follow-up by public health inspectors implicated either a visit to a petting farm 5 August, 2001 or the consumption of unpasteurized goat's milk. No other food source seemed to be implicated. Two other children from the same family (ages 2 and 7) also became ill with bloody diarrhea within 2 to 4 days of the first child falling ill.

The family with the three ill children had joined the co-operative 3 months earlier. Two children from another family, visiting the co-operative farm, also became infected. Two of these five infected children were hospitalized and developed hemolytic-uremic syndrome.

Two 1 litre glass bottles of milk from a batch of seven bottles purchased by the first family on 5 August, 2001 were sent to the Food Poisoning section, British Columbia Centre for Disease Control Society (BCCDCS) Laboratory Services on 17 August, 2001. Milk was enriched in Doyle's broth overnight at 44.5EC and the following morning one bottle was found presumptively positive by VIP^® (BioControl Systems, Inc.), a visual immunoprecipitate assay that detects enterohemorraghic E. coli. Subsequent isolation of typical colorless colonies on sorbitol MacConkey agar (E. coli O157:H7 does not ferment sorbitol) were identified as verotoxin gene positive E. coli O157:H7 in the Enterics section, BCCDCS Laboratory Services. All three stools samples received from infected individuals matched the fingerprinting by pulsed field gel electrophoresis (PFGE) subtyping pattern found in the goat's milk (Figure 1). Of interest, fifteen typical colonies picked from direct plates (before enrichment) were not found to be E. coli O157:H7 biochemically. This observation, and failure to isolate E. coli from the second bottle of milk indicates the pathogenic E. coli O157:H7 was present in low numbers in the milk.

On 23 August, 2001 an advisory for raw milk suspected in this E. coli O157:H7 outbreak was issued by the Acting Medical Health Officer in the CVIHR. No further cases were identified. Commercial pasteurization of milk was first introduced in 1895 after Louis Pasteur discovered the process inactivated spoilage organisms in wine. Today milk is pasteurized both to destroy pathogenic bacteria that may be present, and to improve the shelf life⁽¹⁾. Pasteurization of milk is required by law in B.C.

Although the link between consumption of raw milk and disease is well established for several organisms (E. coli, Campylobacter,  Listeria, Salmonella, Staphylococcus, Yersinia)⁽²⁾, there are still uninformed individuals who persist in the belief that raw dairy products are healthier, and that pasteurized products are less beneficial, and even harmful.

References

1. Wang G, Zhao T, Doyle MP. Survival and growth of Escherichia coli O157:H7 in unpasteurized and pasteurized milk. J Food Protection 1997;60:610-13.

2. Vasavada PC. Pathogenic bacteria in milk - a review. J Dairy Science 1987;71:2809-16.

Source: L McIntyre, BSc, Supervisor, Food Poisoning, Laboratory Services; J Fung, BSc, MSc, Supervisor, Environmental Microbiology,; A Paccagnella, BSc, RT, Supervisor, Enterics; J Isaac-Renton, MD, FRCP(C), Director, Laboratory Services, British Columbia Centre for Disease Control Society, Vancouver; F Rockwell, MD, FRCP(C), Ministry of Health; B Emerson, MD, FRCP(C), Acting Medical Health Officer; T Preston, CPHI(C), Deputy Chief Environmental Health Officer, Central Vancouver Island Health Region, Nanaimo, British Columbia.

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