In November 1987, the toxic dinoflagellate Gymnodinium breve bloomed in North Carolina nearshore waters. This occur rence was the first record of G. breve north of Florida, a range extension of >800 km. We propose the (Gulf of Mexico) Loop Current‐Florida Current‐Gulf Stream system as the transport mechanism for G. breve cells from a late summer bloom off the southwest coast of Florida (Charlotte Harbor‐Sarasota). The estimated transit time for cells around the peninsula and northward to the continental shelf off North Carolina is 22–54 d. About 30 d after the Charlotte Harbor‐Sarasota bloom, satellite images of sea‐surface temperature substantiated the shoreward movement of a filament of Gulf Stream water onto the narrow continental shelf between Cape Hatteras and Cape Lookout. This filament, the likely source of G. breve cells, remained in nearshore waters and was identifiable in satellite images for >19 d. Once the bloom was inshore, both windspeed and direction were important in determining its distribution.

Filter feeding shellfish can concentrate pathogenic bacteria, including Vibrio vulnificus and Vibrio parahaemolyticus, as much as 100-fold from the overlying water. These shellfish, especially clams and oysters, are often consumed raw, providing a route of entry for concentrated doses of pathogenic bacteria into the human body. The numbers of foodborne infections with these microbes are increasing, and a better understanding of the conditions that might trigger elevated concentrations of these bacteria in seafood is needed. In addition, if bacterial concentrations in water are correlated with those in shellfish, then sampling regimens could be simplified, as water samples can be more rapidly and easily obtained. After sampling of oysters and clams, either simultaneously or separately, for over 2 years, it was concluded that while Vibrio concentrations in oysters and water were related, this was not the case for levels in clams and water. When clams and oysters were collected simultaneously from the same site, the clams were found to have lower Vibrio levels than the oysters. Furthermore, the environmental parameters that were correlated with levels of Vibrio spp. in oysters and water were found to be quite different from those that were correlated with levels of Vibrio spp. in clams.IMPORTANCE This study shows that clams are a potential source of infection in North Carolina, especially for V. parahaemolyticus. These findings also highlight the need for clam-specific environmental research to develop accurate Vibrio abundance models and to broaden the ecological understanding of clam-Vibrio interactions. This is especially relevant as foodborne Vibrio infections from clams are being reported.KEYWORDS clams, ecology, food, oysters, shellfish, Vibrio A n estimated 84,000 people contract foodborne Vibrio infections each year in the United States, resulting in 500 hospitalizations and 100 deaths (1, 2). Unlike most other major foodborne bacterial pathogens, the number of cases caused by Vibrio spp. is increasing and currently is the highest since national reporting began (2, 3). While at least 12 Vibrio spp. are potentially pathogenic to humans, the two foodborne Vibrio spp. that cause the most infections and the most deaths in the United States are Vibrio parahaemolyticus and Vibrio vulnificus, respectively (2, 4).V. vulnificus is the single most fatal foodborne pathogen in the United States, and perhaps the world (4), accounting for 95% of all U.S. seafood-related deaths, with a fatality rate approaching 50% (5). Infections resulting from ingestion typically produce symptoms such as fever, chills, nausea, abdominal pain, hypotension, and the development of secondary lesions on the extremities (5, 6). V. parahaemolyticus infections are

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Monitoring of Vibrio vulnificus and V. parahaemolyticus abundance is pertinent due to the ability of these species to cause disease in humans through aquatic vectors. Previously, we performed a multiyear investigation tracking Vibrio spp. levels in five sites along the southeastern North Carolina coast. From February 2013 to October 2015, total V. vulnificus and V. parahaemolyticus abundance was measured in water, oysters and clams. In the current study, pathogenic subpopulations were identified in these isolates using molecular markers, revealing that 5.3% of V. vulnificus isolates possessed the virulence-correlated gene (vcgC), and 1.9% of V. parahaemolyticus isolates harbored one or both of the virulence-associated hemolysin genes (tdh and trh). Total V. parahaemolyticus abundance was not sufficient to predict the abundance of pathogenic subpopulations. Specifically, pathogenic V. parahaemolyticus isolates were more often isolated in cooler waters and were sometimes isolated when no other V. parahaemolyticus strains were detectable. Vibrio vulnificus clinical (C-) genotypes correlated with total V. vulnificus; however, salinity, water depth and total suspended solids influenced C- and E-genotypes differently. Lastly, we documented individual oysters harboring significantly higher V. vulnificus levels for which there was no ecological explanation, a phenomenon that deserves closer attention due to the potentially elevated health hazard associated with these 'hot' shellfish.

The United States has federal regulations in place to reduce the risk of seafood-related infection caused by the estuarine bacteria Vibrio vulnificus and Vibrio parahaemolyticus. However, data to support the development of regulations have been generated in a very few specific regions of the nation. More regionally specific data are needed to further understand the dynamics of human infection relating to shellfish-harvesting conditions in other areas. In this study, oysters and water were collected from four oyster harvest sites in North Carolina over an 11-month period. Samples were analyzed for the abundances of total Vibrio spp., V. vulnificus, and V. parahaemolyticus; environmental parameters, including salinity, water temperature, wind velocity, and precipitation, were also measured simultaneously. By utilizing these data, preliminary predictive management tools for estimating the abundance of V. vulnificus bacteria in shellfish were developed. This work highlights the need for further research to elucidate the full suite of factors that drive V. parahaemolyticus abundance. In the United States, it is estimated that as many as 84,000 people annually contract food-borne infections caused by Vibrio bacteria (1). These aquatic bacteria are found in coastal or estuarine environments as part of the natural flora but can become highly concentrated in filter-feeding sea life, including shellfish such as oysters (2, 3). Because oysters are often consumed raw or undercooked, vibrios concentrated within the oysters remain viable and infectious. Reported infections from food-borne Vibrio spp. are on the rise and are currently at the highest level since tracking began (4). While no fewer than 12 species of Vibrio are capable of infection, the 2 most common in the United States are Vibrio parahaemolyticus and Vibrio vulnificus, which cause the most infections and the most deaths, respectively (5-7). Symptoms associated with infections caused by these two species range from gastroenteritis to grievous wound infections or primary septicemia, with case fatality rates as high as 50% (2, 7-11).Both of these important bacterial species have been reported to exhibit seasonality, with warmer water temperatures resulting in increased Vibrio occurrence and concentrations in oysters (12-15). As a consequence, more than 75% of the infections caused by Vibrio spp. in the United States are observed between May and October (14). While no maximum environmental temperature has been reported, the minimum water temperature needed for the isolation of culturable V. vulnificus from oysters differs among studies but is most often reported in the range of 12 to 17°C; however, lower temperatures have also been documented in individual studies (3,12,13,(15)(16)(17)(18)(19)(20). Similarly, V. parahaemolyticus can grow in culture at a minimum temperature of approximately 10°C (21). The typical minimum water temperatures associated with oyster-related human disease reported for V. vulnificus and V. parahaemolyticus are ca. 20°C and 15°C, respectiv...