An outbreak of Campylobacter illness involving two cases and implicating consumption of raw oysters, was first reported to the Maine Center for Disease Control and Prevention (ME CDC) in early July 2024. The ME CDC, Maine Department of Marine Resources (ME DMR) and the Maine Department of Health and Human Services Health Inspection Program initiated an investigation that eventually linked six confirmed cases to the consumption of raw oysters from two aquaculture lease sites in the same harvest area in Freeport, ME. The ME CDC Health and Environmental Testing Laboratory identified the causative agent as Campylobacter coli in two clinical isolates from the first and third reported illnesses. Whole genome sequencing was utilized to compare the two clinical isolates revealing a 0 single nucleotide polymorphism (SNP) difference and definitively linking the cases.
The illness investigation included six case interviews by field epidemiologists, facility inspections at a dozen retail locations and shellfish dealers, four in-field inspections of aquaculture operations and one in-field inspection of an open water wet storage site. After a review of the known pollution sources and water quality data for the shellfish growing area, it was hypothesized that the likely source of contamination was wild birds which regularly perched on the floating surface bags used to grow oysters at both implicated aquaculture lease sites. A recall of oysters from the two implicated aquaculture lease sites was initiated on July 17th for product harvested between June 19th and July 16th.
ME DMR instructed the aquaculture lease holders to modify their operation plans and incorporate submergence of their product for 14 days prior to harvest. To support reopening the lease sites, the DMR public health laboratory collected oyster samples from the floating surface bags and from the submerged cages and tested them for fecal coliform, an indicator species routinely used in the National Shellfish Sanitation Program. Results indicated that levels of fecal coliform in oyster meats collected from the floating surface bags were sporadically high (2400 MPN/100g) and also showed that submerging the oysters for 14 days consistently decreased fecal coliform levels. The investigation was concluded and both aquaculture lease sites were reopened almost a month after the first illnesses were reported. No additional cases were linked to this outbreak.