Information for Health Professionals & Laboratorians

Clinical features
Wound Infections
Vibrio vulnificus should be considered for infected wounds that were exposed to coastal waters. To improve survival, antibiotic treatment should be initiated immediately and aggressive attention should be given to the wound site.

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Vibriosis is typically characterized by watery diarrhea, usually with abdominal cramping, nausea, vomiting, and fever. Vibrio bacteria can also cause wound or soft tissue infections. In persons with underlying medical conditions, especially liver disease, Vibrio bacteria can cause bloodstream infections characterized by fever, chills, dangerously low blood pressure, blistering skin lesions, and sometimes death.

Etiologic agent

Vibrio bacteria are gram-negative bacteria that grow well in salty environments, such as seawater.  They are naturally and commonly found in warm marine and estuarine environments.

About a dozen Vibrio species can cause human illness. Illnesses caused by Vibrio cholerae O1 and O139 strains that produce cholera toxin are defined by the World Health Organization as cholera; illnesses caused by other Vibrio strains are called vibriosis.

Incidence

An estimated 80,000 cases of vibriosis, 500 hospitalizations, and 100 deaths occur in the United States each year, with most not confirmed by culture.

Sequelae

Most people with mild illness typically recover after about 3 days and suffer no long-term consequences. V. vulnificus infections are fatal about 20% of the time and can cause bloodstream infections in people with liver disease.

Transmission

People can develop vibriosis from eating raw or undercooked shellfish, particularly oysters. Wound infections may occur when wounds or soft tissues are exposed to salt water or brackish water.

Risk groups

Anyone can get vibriosis. People with underlying conditions, such as alcoholism and liver disease, are at increased risk of infection and serious complications.

Surveillance

Surveillance for infections began in the Gulf Coast states of Alabama, Florida, Louisiana, and Texas in 1989, and expanded to include FoodNet sites in 1996. In January 2007, infections caused by V. parahaemolyticus and other Vibrio species became nationally notifiable.

Trends

Infections occur throughout the year; approximately 80% occur from May through October when water temperatures are warmer. Large U.S. outbreaks linked to the consumption of raw oysters occurred in 1997, 1998, 2006, and 2012. Environmental factors, such as temperature and salinity, can influence growth of Vibrio bacteria.

Challenges

Many people like to eat oysters and other shellfish raw. Large outbreaks have occurred even when counts of V. parahaemolyticus in oysters from implicated harvest sites were very low. Therefore, monitoring and responding to elevated counts of V. parahaemolyticus in the harvesting waters and in shellfish does not completely protect the public’s health.

Opportunities

Implementing quick cooling of shellfish after harvesting and refrigeration and maintaining refrigeration until consumption can reduce growth of Vibrio bacteria. Standards used for closing and re-opening of oyster beds are being revised to account for environmental factors that affect vibriosis risk. Education can focus on the risks associated with consumption of raw and undercooked shellfish, especially in warm months. Other locations can follow California’s lead in restricting the sale of raw oysters harvested from the Gulf Coast during the seven warmest months to only oysters that have been treated with postharvest processing.

LABORATORY GUIDANCE

Diagnosis of Vibrio infection is confirmed by isolation of the bacteria. CDC recommends the use of selective media, such as thiosulfate citrate bile-salts (TCBS) agar, for examining stool specimens.

Reporting a Foodborne Illness