Public Health Impact of Vibrio vulnificus Infections
Vibrio vulnificus infections normally occur as sporadic cases, not as outbreaks, which are defined as two or more cases. In the last seven years, an average of 89 U.S. V. vulnificus infections per year was reported to the Centers for Disease Control and Prevention.
U.S. V. vulnificus Cases by Year 1998 - 2004
Of the total V. vulnificus cases in the bar graph above, approximately 60% were wound infections and roughly 40% were linked to eating raw or undercooked molluscan shellfish (oysters, clams, mussels). In an analysis of 326 U.S. shellfish cases reported from 1993 to 2003, 94% of cases were associated with raw oysters, 4% with undercooked oysters, and 2% with clams or other shellfish 1.
Seasonality and Geographic Distribution of Shellfish Consumption Cases
Because V. vulnificus bacteria flourish in Gulf of Mexico seawater during warm weather months, infections show a seasonal trend with shellfish cases rising significantly in April, peaking in August, and decreasing in November (refer to bar graph below)
U.S. V. vulnificus Shellfish Cases by Month 1995-2004
Since warm Gulf of Mexico seawater provides optimum conditions for V. vulnificus growth, states bordering the Gulf or adjacent states usually report the most wound and shellfish consumption V. vulnificus cases. During the seven year period ending in 2004, Florida reported 69 shellfish consumption cases, Texas reported 40, Georgia, 25 cases, Louisiana, 19, and Alabama, 8.
Shellfish-Related V. vulnificus Cases by Reporting States 1998-2004
Even though California does not border any Gulf coast states, raw Gulf oysters are popular with Hispanic consumers. Consequently, California reported 29 shellfish consumption V. vulnificus cases between 1998 and 2004. In an effort to reduce V. vulnificus cases, beginning in April 2003 California banned the sale of raw Gulf oysters from April through October, unless they are processed to reduce the level of V. vulnificus bacteria to non-detectable (post-harvest processed oysters). Some experts believe that numbers of V. vulnificus illnesses, as well as all food-borne illnesses, are underreported.
Physician Reporting Requirements
It is important to report cases of V. vulnificus infection to local and state health authorities so that incidence of illness can be tracked by the U.S. Food and Drug Administration and Centers for Disease Control and Prevention and possible prevention strategies can be developed and/or evaluated. Many, but not all U.S. states require doctors, hospitals, and/or labs to report confirmed cases of V. vulnificus and other Vibrio infection to their state health agencies. View individual state reporting requirements by accessing the Council of State and Territorial Epidemiologists's webpage (select Vibrio vulnificus as the disease/condition, and search by state, district, or territory).
Susceptibility and Mortality
Healthy people without chronic high-risk conditions are not at risk for consumption-related, serious V. vulnificus infection. If healthy people are infected from eating raw molluscan shellfish, their symptoms are usually mild and temporary (gastroenteritis); they rarely require hospitalization (2). However, healthy people are at risk for developing cellulitis from V. vulnificus infected wounds.
People with chronic high-risk conditions are susceptible to severe infection from physical contact with salt and brackish water and seafood and consumption of raw molluscan shellfish (oysters, clams, mussels) and are usually brought to hospital emergency rooms. Statistical analysis of 326 shellfish consumption cases in the United States from 1993 to 2003 (1) shows an average 53% mortality rate. However, when shellfish cases are grouped according to pre-existing conditions, higher mortality rates are revealed for alcoholics (67%) and people with liver disease (61%). Liver disease is a pre-existing condition in 53% of the shellfish consumption cases.
Demographics of Shellfish Consumption Cases
Statistical analysis of 326 U.S. shellfish consumption V. vulnificus cases from 1993 to 20031 showed that 87% of patients were males. The mean age for males and females was 53 and 55 years, respectively. Sixty-four percent of V. vulnificus patients were white, 17% Hispanic, 6% black, 4% Asian, and 9% were of unknown ethnic group. However, in California, 88% of patients were Hispanic, and in Texas, 21% were Hispanic. In Louisiana, 13% were Asians.
The typical U.S. shellfish-consumption V. vulnificus case profile is a middle-aged, white man who is a heavy drinker and either is unaware of or ignores dietary risks. He consumes three to twelve raw oysters and develops septicemia3.
- Bashin, M. 2004. Vibrio vulnificus Case Analysis 1993 - 2003 (unpublished report). Interstate Shellfish Sanitation Conference.
- Interstate Shellfish Sanitation Conference. 2003.Vibrio vulnificusFact Sheet for Health Care Providers*
- Tamplin, M., R. Hammond, P. Gulig, R. Baker. 2001. Vibrio vulnificus, a hidden risk in raw oysters (video). A clinician's guide to V. vulnificus infection and treatment. (Request via Interstate Shellfish Sanitation Conference order form.)*