BACKGROUND: Raw seaweed is popular in Hawaiian and Asian cuisines; aquaculture farming of seaweed has not previously been implicated as a source for foodborne illness. In October 2016, the Hawaii Department of Health (HDOH) State Laboratories Division (SLD) identified a cluster of Salmonella enterica, serovar Weltevreden cases with a rare XbaI pulsed-field gel electrophoresis (PFGE) pattern. We present our investigation linking a salmonellosis outbreak to a single aquaculture farm on Oahu.
METHODS: A case was defined as a S. Weltevreden infection with isolate XbaI pattern JQPX01.0061 and illness onset in October 2016 or later. Cases were interviewed using a standardized questionnaire on possible exposures and foods consumed before infection. Product traceback was performed for suspect foods. Environmental and product samples, collected from an implicated producer, were screened for Salmonella using an enzyme-linked fluorescent assay. Organisms were then isolated, identified, serotyped, and analyzed by PFGE.
RESULTS: Fifteen cases were identified with onset dates ranging from October 15–31, 2016. Median case age was 37 years (range 8–88 years). Nine (60%) were female; four (27%) were hospitalized. Thirteen (87%) cases reported consuming limu poke—a dish comprising raw fish and seaweed—in the week before onset. The seaweed was traced back to one aquaculture farm on Oahu. One (8%) of 12 seaweed samples and 10/36 (28%) water samples collected from the farm were positive for Salmonella (9 S. Weltevreden, 2 S. Oslo); PFGE patterns from environmental S. Weltevreden isolates were closely related, but distinct from the clinical isolate pattern. Site assessment for potential risk factors for bacterial contamination revealed a neighboring wildlife refuge, lack of bathroom and handwashing facilities, and the harvesting of seaweed from uncontrolled streams. A cease and desist order was issued, and a product recall initiated. The farm was allowed to resume operations after remediation was complete and subsequent environmental screening was negative for Salmonella.
CONCLUSIONS: This outbreak demonstrates aquaculture products such as seaweed are potential vehicles for Salmonella; although the outbreak strain was distinct from environmental isolates, detection of multiple serotypes and clonal variants throughout the farm suggested conditions permitting Salmonella contamination and subsequent dissemination. Seaweed should be considered a potential foodborne risk because of its tendency to be consumed raw, and because aquaculture may be susceptible to environmental or human contamination, particularly when conditions are not well-controlled.