Molecular confirmation of oysters as the vector for hepatitis A in a 2005 multistate outbreak

Numerous hepatitis A outbreaks were linked to the consumption of raw molluscan shellfish in the United States between 1960 and 1989. However, there had been no major molluscan shellfish-associated hepatitis A outbreaks reported in the United States for more than a decade (1989 to 2004). Beginning in late August 2005, at least 10 clusters of hepatitis A illnesses, totaling 39 persons, occurred in four states among restaurant patrons who ate oysters. Epidemiologic data indicated that oysters were the source of the outbreak. Traceback information showed that the implicated oysters were harvested from specific Gulf Coast areas. A voluntary recall of oysters was initiated in September. Hepatitis A virus (HAV) was detected in multiple 25-g portions in one of two recalled samples, indicating that as many as 1 of every 15 oysters from this source was contaminated. Comparing 315 nucleotides within the HAV VPl-2B region, 100% homology was found among four amplicons recovered from a total of six independent experiments of the implicated oysters, and an identical HAV sequence was detected in sera from all 28 patient serum specimens tested. Ten percent heterogeneity over 315 nucleotides (31 variants) was observed between the outbreak strain (subgenotype 1A) and an HM-175 strain (subgenotype 1B) used in the laboratory where the oysters were processed. To our knowledge, this investigation is the first in the United States to identify an HAV-identical strain in persons with hepatitis A as well as in the food that was implicated as the source of their infections.

Effects of a commercial heat-shock process on Vibrio vulnificus in the American oyster, Crassostrea virginica, harvested from the Gulf Coast

Oysters (Crassostrea virginica) harvested from the Gulf Coast, containing 10(2) to 10(4) most probable number (MPN) per gram of Vibrio vulnificus, were subjected to a commercial heat-shock process. After 1 to 4 min at internal oyster meat temperatures exceeding 50 degrees C, shellstock oysters were shucked, chilled, washed, and packed. V. vulnificus and total bacterial levels in Gulf Coast oysters were significantly reduced from 1 to 4 logs in the finished product. Similar reductions were not observed in shellstock oysters that were subject to conventional processing. Under the National Shellfish Sanitation Program, heat shocking is an acceptable process to use to assist in the shucking of shellstock. This research revealed that the heat-shock process may also serve to significantly reduce V. vulnificus in summer Gulf Coast oysters.

Influence of water temperature and salinity on Vibrio vulnificus in Northern Gulf and Atlantic Coast oysters (Crassostrea virginica)

This study investigated the temperature and salinity parameters associated with waters and oysters linked to food-borne Vibrio vulnificus infections. V. vulnificus was enumerated in oysters collected at three northern Gulf Coast sites and two Atlantic Coast sites from July 1994 through September 1995. Two of these sites, Black Bay, La., and Apalachicola Bay, Fla., are the source of the majority of the oysters implicated in V. vulnificus cases. Oysters in all Gulf Coast sites exhibited a similar seasonal distribution of V. vulnificus: a consistently large number (median concentration, 2,300 organisms [most probable number] per g of oyster meat) from May through October followed by a gradual reduction during November and December to < or = 10 per g, where it remained from January through mid-March, and a sharp increase in late March and April to summer levels. V. vulnificus was undetectable (< 3 per g) in oysters from the North and South Carolina sites for most of the year. An exception occurred when a late-summer flood caused a drop in salinity in the North Carolina estuary, apparently causing V. vulnificus numbers to increase briefly to Gulf Coast levels. At Gulf Coast sites, V. vulnificus numbers increased with water temperatures up to 26 degrees C and were constant at higher temperatures. High V. vulnificus levels (> 10(3) per g) were typically found in oysters from intermediate salinities (5 to 25 ppt). Smaller V. vulnificus numbers (< 10(2) per g) were found at salinities above 28 ppt, typical of Atlantic Coast sites. On 11 occasions oysters were sampled at times and locations near the source of oysters implicated in 13 V. vulnificus cases; the V. vulnificus levels and environmental parameters associated with these samples were consistent with those of other study samples collected from the Gulf Coast from April through November. These findings suggest that the hazard of V. vulnificus infection is not limited to brief periods of unusual abundance of V. vulnificus in Gulf Coast oysters or to environmental conditions that are unusual to Gulf Coast estuaries.

Phages infecting Vibrio vulnificus are abundant and diverse in oysters (Crassostrea virginica) collected from the Gulf of Mexico

Phages infecting Vibrio vulnificus were abundant (> 10(4) phages g of oyster tissue-1) throughout the year in oysters (Crassostrea virginica) collected from estuaries adjacent to the Gulf of Mexico (Apalachicola Bay, Fla.; Mobile Bay, Ala.; and Black Bay, La.). Estimates of abundance ranged from 10(1) to 10(5) phages g of oyster tissue-1 and were dependent on the bacterial strain used to assay the sample. V. vulnificus was near or below detection limits (< 0.3 cell g-1) from January through March and was most abundant (10(3) to 10(4) cells g-1) during the summer and fall, when phage abundances also tended to be greatest. The phages isolated were specific to strains of V. vulnificus, except for one isolate that caused lysis in a few strains of V. parahaemolyticus. Based on morphological evidence obtained by transmission electron microscopy, the isolates belonged to the Podoviridae, Styloviridae, and Myoviridae, three families of double-stranded DNA phages. One newly described morphotype belonging to the Podoviridae appears to be ubiquitous in Gulf Coast oysters. Isolates of this morphotype have an elongated capsid (mean, 258 nm; standard deviation, 4 nm; n = 35), with some isolates having a relatively broad host range among strains of V. vulnificus. Results from this study indicate that a morphologically diverse group of phages which infect V. vulnificus is abundant and widely distributed in oysters from estuaries bordering the northeastern Gulf of Mexico.

Offshore suspension relaying to reduce levels of Vibrio vulnificus in oysters (Crassostrea virginica)

Oysters naturally contaminated with 10(3) to 10(4) most probable numbers (MPN) of Vibrio vulnificus per g were relayed to offshore waters (salinity, 30 to 34 ppt), where they were suspended in racks at a depth of 7.6 m. V. vulnificus counts in oysters were reduced to < 10 MPN/g within 7 to 17 days in five of the six studies. At the end of the studies (17 to 49 days), V. vulnificus levels were reduced further and ranged from a mean of 0.23 to 2.6 MPN/g. Oyster mortalities during relaying were < 6%. The reduction of V. vulnificus in relayed oysters is associated with exposure to high-salinity environments essentially devoid of V. vulnificus. Offshore suspension relaying may be a method that industry can employ to reduce V. vulnificus levels in raw Gulf Coast oysters.

Comparison of APHA and elevated temperature enrichment methods for recovery of Vibrio cholerae from oysters: collaborative study

Two methods (the American Public Health Association (APHA) method and the elevated temperature method) for recovery of Vibrio cholerae from oysters were compared in a collaborative study. Oysters were inoculated with high (about 150 cells/g) and low (about 20 cells/g) levels of V. cholerae. The elevated temperature method gave a significantly higher (P less than 0.05) recovery rate and showed greater specificity (P less than 0.01), as determined by the confirmation rate of suspect colonies. The elevated temperature method required only 25% of the labor and materials necessary for the APHA method. The elevated temperature method has been adopted official first action.

Distribution of Vibrio cholerae in the Apalachicola (Florida) Bay Estuary

Vibrio cholerae non-O1 was found throughout the Apalachicola, FL, estuary. V. cholerae O1 was isolated primarily at the City of Apalachicola sewage treatment plant, Scipio Creek and the north shore of St. George Island. Highest concentrations of both serogroups occurred in August and November. Concentrations were lowest in February and increased substantially in May. A cholera toxin-like toxin was not detected in any of the V. cholerae cultures by the Y-1 mouse adrenal cell assay or the enzyme-linked immunosorbent assay (ELISA). However, 35% of the V. cholerae O1 and 22% of the V. cholerae non-O1 cultures selected for testing caused diarrhea in infant rabbits. The proportion of V. cholerae O1 and non-O1 isolates pathogenic to infant rabbits increased as water temperature decreased. Fecal coliforms appeared to be more useful than total coliforms as indicators of the numbers of V. cholerae in water, but neither of those National Shellfish Sanitation Program indicator groups ensured against the presence of pathogenic V. cholerae in shellfish-growing areas.

Non-O1 Vibrio cholerae in Shellfish, Sediment and Waters of the U.S. Gulf Coast

In a study conducted throughout U.S. Gulf Coastal waters, Vibrio cholerae non-O1 was isolated more frequently from water samples than from shellfish or sediment samples. Frequency of V. cholerae recovery was directly related to water temperature and inversely related to salinity. The presence of V. cholerae was not adequately indicated by the fecal coliform standards for shellfish-growing waters and market shellfish as established by the National Shellfish Sanitation Program. Although all cultures tested by the Y-1 mouse adrenal cell assay or by radioimmunoassay for production of a cholera toxin-like toxin were negative, 4 of 13 isolates caused diarrhea in the infant rabbit.

Isolation of Vibrio cholerae serotype Ogawa from a Florida estuary

Vibrio cholerae serotype Ogawa was recently isolated from the estuarine waters of Apalachicola Bay, Fla., in areas that are subject to consistent fecal contamination and in areas that are remote from any apparent source of contamination. The significance of these organisms in the environment has not been determined.