On June 27, 2011, the Alaska Section of Epidemiology (SOE) released an Epidemiology Bulletin detailing an outbreak of campylobacteriosis associated with the consumption of raw milk from Farm A in the Mat-Su Valley.1 This follow-up Bulletin provides updated information about the investigation.
Active Case finding
On June 24, SOE distributed an Advisory through the Public Health Alert Network (PHAN) to alert health care providers of the outbreak and to recommend testing for Campylobacter in patients who present with acute gastrointestinal (GI) illness and a history of raw milk consumption. Through the PHAN, the June 27 Bulletin, and associated press releases, members of the public were also asked to contact SOE and report acute GI illness following consumption of raw milk. SOE received calls from five community members reporting current and previous GI illness among persons in their households with a preceding history of consuming Farm A raw milk or cream. Public health nurses facilitated collection of stool specimens from recently ill persons for enteric bacterial pathogen testing at the Alaska State Public Health Laboratory (ASPHL).
Stool specimens were collected from six persons with recent GI illness and consumption of Farm A raw dairy products. Three of the six samples tested positive for Campylobacter jejuni; all isolates were the same rare strain of C. jejuni found in the four other laboratory-confirmed cases in this outbreak (pulsed-field gel electrophoresis [PFGE] pattern AKDBRS16.0166/AKDBRK02.0093). These three persons shared raw dairy products obtained from Farm A during the first week of July. A total of 11 persons who reported acute GI illness with routine consumption of Farm A dairy products but were not-laboratory confirmed were considered to have suspected campylobacteriosis (Figure).
Farm A bulk tank milk samples collected on June 22 and 27 tested negative for C. jejuni, but positive for Listeria monocytogenes. None of the Farm A raw milk that was actually consumed by ill persons was available for testing.
The identical rare strain of C. jejuni has been identified in all laboratory-confirmed patients associated with this outbreak and Farm A cow manure specimens. These laboratory findings combined with the epidemiologic finding that Farm A raw dairy product consumption is the only exposure common to all seven laboratory-confirmed cases (and the 11 suspect cases) affirms the conclusion that this outbreak is due to consumption of Farm A raw dairy products. Contamination might have resulted from introduction of manure into the milk or cream at some point in time from milking to filling the containers, or a cow (or cows) with an infected udder may be intermittently shedding Campylobacter directly into the milk. Regardless of the exact mechanism of contamination, with confirmed cases reporting consumption of dairy products over an 8-week period from May to July, this outbreak poses an ongoing threat to Farm A raw dairy product consumers.
It is not surprising that C. jejuni was not detected in Farm A bulk tank samples because C. jejuni is notoriously difficult to culture from environmental specimens other than raw stool,2 and few campylobacteriosis outbreak investigations yield laboratory confirmation of an implicated food source such as raw milk or produce.3 Furthermore, none of the raw milk that was actually consumed by ill persons prior to their illness onset was available for testing. Numerous C. jejuni strains were detected on Farm A, which was anticipated given that many farm animals are known reservoirs for the bacteria. Finding only a single or predominant strain shared by the human cases is not unusual, and might relate to factors associated with seasonality or adaptation of the strain to humans.4 Finally, as was the case in May, the Farm A raw milk samples collected in June tested positive for L. monocytogenes, which can cause life-threatening meningitis in children and persons with compromised immune systems.
Environmental and Milk Testing Results
Eleven composite cow manure samples, one composite chicken manure sample, and one swab from the milking parlor drain were collected on June 22. ASPHL cultured the samples with guidance from the Centers for Disease Control and Prevention (CDC) Campylobacter Laboratory. Any culture suspicious for Campylobacter growth had up to six colonies chosen and plated for identification. From the 13 samples collected at the farm and submitted for culture, 18 separate colonies were identified as C. jejuni and underwent PFGE analysis; seven different PFGE patterns were identified. PFGE pattern AKDBRS16.0166/AKDBRK02.0093 was isolated in manure samples from the grazing field and the calf barn; this pattern was identical to the pattern of the C. jejuni isolated from the seven laboratory-confirmed patients.