Six people were sickened and two were hospitalised, said the Morbidity and Mortality Weekly Report (MMWR) at the Centers for Disease Control and Prevention (CDC).
A Vermont Department of Health (VDH) investigation found that the patients had been exposed to raw or lightly cooked chicken livers produced at the same poultry factory (establishment A) and livers collected yielded the outbreak strain of C. jejuni.
In October 2012 the VDH identified three cases of laboratory-confirmed Campylobacter jejuni infection in Vermont residents; the isolates had indistinguishable pulsed-field gel electrophoresis (PFGE) patterns.
PulseNet, the molecular subtyping network for foodborne disease surveillance, led to one additional case from New Hampshire, New York, and Vermont reported in the preceding six months.
Farm worker exposed
One of the people was exposed to the pathogen while working on the farm, the other four cases became ill after eating the livers, which were deliberately undercooked to maintain their texture.
USDA-FSIS found that establishment A, which stopped selling chicken livers, used antimicrobial cleaners to the livers, these efforts only affect the external surfaces and because Campylobacter contamination can be internal, the safety of undercooked chicken livers was not assured.
A food safety assessment conducted by the US Department of Agriculture's Food Safety and Inspection Service (USDA-FSIS) found no major violations.
The Food and Drug Administration (FDA) says that poultry must reach an internal temperature of 165oF (73.9oC) for at least 15 seconds.
Studies have shown that 77% of retail chicken livers are contaminated with Campylobacter and contamination is usually in internal tissues as well as on the surface.
The six patients ranged in age from 19 to 87 years; three were female. Two were hospitalized, but all six had recovered by the time of their interviews.
Frozen chicken livers collected from restaurant A were sent to the VDH laboratory, minced into 13 25-gram subsamples and enriched as normal for the Campylobacter immunoassay.
Two of the 13 subsamples screened for Campylobacter gave positive results, but the pathogen could not be recovered in culture.
VDH collected fresh chicken livers from establishment A and delivered them to the VDH laboratory, where they were processed.
C. jejuni was recovered from these chicken livers, and one isolate had PFGE patterns indistinguishable from the outbreak strain.
Additional characterization of the six human isolates and one chicken liver isolate by antimicrobial susceptibility testing identified the strain as susceptible to eight of nine antimicrobials tested on the CDC National Antimicrobial Resistance Monitoring System panel, but resistant to tetracycline.
Poultry-associated campylobacteriosis is the pathogen-food pair estimated to be responsible for the greatest burden of foodborne disease in the US.
However, outbreaks of Campylobacter are rare, with only 1.9% of foodborne outbreaks reported to the CDC attributed to this pathogen.