Multi-State Vibrio Parahaemolyticus Outbreak Associated with Consumption of Raw Oysters Harvested from Oyster Bay Harbor

BACKGROUND:  

Vibrio parahaemolyticus (Vp) causes an estimated 35,000 domestically acquired foodborne illnesses annually. Consumption of raw oysters has been implicated in several large Vp outbreaks, last in 2006.

METHODS:

In June 2012, the first of three Vp clusters was reported to CDC; all patients reported consumption of oysters from Oyster Bay Harbor (OBH), New York. Subsequent reports of two Vp clusters with indistinguishable pulsed-field gel electrophoresis (PFGE) subtypes in two other states prompted additional case finding using both the Cholera and Other Vibrio Illness Surveillance (COVIS) system and PulseNet, the national molecular subtyping database. The three clusters were determined to be part of a single outbreak. An outbreak-associated case was defined as Vp illness with onset between April 24 and August 3, 2012 in a person who reported consuming seafood in the 7 days before illness onset.  PFGE subtyping and molecular serotyping were performed on patient isolates. Cases were categorized as confirmed or probable based on available microbiological, food history, and seafood traceback data.

RESULTS:

Twelve confirmed and 16 probable outbreak-associated cases were reported. Illness onset dates ranged from May 27 to July 20, 2012.  The median age of patients was 49 years (range, 18-83 years), and 46% were female. Two patients (8%) were hospitalized; none died. Twenty-three (82%) patients reported consuming molluscan shellfish (57% oysters only, 22% clams only, and 4% oysters and clams). For the 20 (71%) cases associated with molluscan shellfish with known harvest information, traceback investigation determined that 65% of molluscan shellfish were definitely from OBH, and 20% were possibly from OBH. Harvest area was unknown for molluscan shellfish associated with 29% of cases.  PFGE pattern combination K16S12.0042/K16N11.0010 was predominant (96%).  Vp serotype O4:Kuk was identified in 77% of patient isolates and one oyster sample from OBH. Sampling of shellfish from OBH indicated that Vp counts were above historical levels. In response to the outbreak, OBH was temporarily closed to shellfish harvesters until weekly environmental sampling indicated Vp counts returned to normal.

CONCLUSIONS:

This is the first multistate outbreak of Vp illnesses reported in the United States almost a decade. Closure of OBH to shellfish harvesting while Vp levels were elevated appears to have controlled the outbreak. Integration of microbiological, food history, and seafood traceback information is necessary for successful investigation of vibriosis outbreaks. Collection and analysis of these data requires coordination among public health and regulatory officials across all jurisdictions.