Frequently Asked Questions about Vibrio
What are Vibrio?
Vibrio are bacteria that naturally occur in coastal waters and are more abundant during the summer as the water warms. While many Vibrio species are harmless to humans, there are multiple Vibrio species that can cause human illness. Most notably, Vibrio parahaemolyticus is the leading cause of seafood-associated gastroenteritis in the U.S. and world, and Vibrio vulnificus can cause severe wound infections from contact with brackish and seawater.
Are Vibrio new to Connecticut?
No. Vibrio bacteria are not new to our waters and have historically resulted in sporadic wound infections (Vibrio vulnificus) and gastrointestinal illnesses (Vibrio parahaemolyticus).
What is the difference between Vibrio parahaemolyticus and Vibrio vulnificus?
Scientists classify organisms by their similarities and differences. Vibrio is a genus with over 100 species. These Vibrio species are similar but have distinct characteristics. These differences impact the species' ability to cause human illnesses and type of illness. Vibrio parahaemolyticus is most commonly associated with self-limiting gastrointestinal illness, but can rarely cause wound infections. Vibrio vulnificus is most commonly associated with wound infections that are not associated with seafood, but can rarely cause seafood-associated illness.
Are Vibrio found in shellfish?
Vibrio are not "shellfish bacteria." Shellfish can accumulate contaminants, including bacteria and viruses, that are present in the water, which is why they are a highly regulated food commodity. The Department of Agriculture, Bureau of Aquaculture (DoAg) is responsible for ensuring all CT shellfish growing waters meet national standards and that CT shellfish in interstate commerce are free of pathogens. The DoAg controls for bacteria, viruses, and contaminants through the state's shellfish sanitation program.
Should I be concerned about Vibrio parahaemolyticus and Vibrio vulnificus in Connecticut?
Connecticut shellfish have never been associated with Vibrio vulnificus infections. In 2013, 104 cases of a specific Pacific coast Vibrio parahaemolyticus strain were associated with an unprecedented outbreak across 13 states, of which 7 were New England states including Connecticut. Since the implementation of statewide Vibrio parahaemolyticus controls in 2014, Connecticut shellfish have not been implicated in an illness outbreak. All Connecticut harvesters continue to annually implement the controls to protect public health. Additional information about Connecticut's control plans can be found here.
Vibrio vulnificus can cause severe infections when open cuts and wounds, including recent surgeries, piercings, and tattooed skin, are exposed to water containing the bacteria. In severe cases, Vibrio vulnificus wound infections can result in limb amputation, sepsis (blood infection), necrotizing fasciitis (tissue death), and death. To minimize the risk of Vibrio vulnificus wound infections, the Connecticut Department of Public Health (DPH) recommends staying out of salt and brackish water when wounds are present, or cover wounds with a waterproof bandage if avoidance is not possible.
I heard about Vibrio in the news in 2023. What were the circumstances?
The CT DPH reported three Vibrio vulnificus infections in 2023. Two of the three were wound infections not associated with seafood. The third infection was a CT resident that consumed raw oysters not harvested from Long Island Sound at an out-of-state establishment. Connecticut shellfish have never been associated with Vibrio vulnificus infections. Two of these individuals, unfortunately, died. Additionally, an individual in Suffolk County, New York, died from a Vibrio vulnificus wound infection.
How can I protect myself while recreational shellfishing in the summer?
In addition to the guidelines above regarding wound infections, protective gloves can be worn when crabbing, fishing, and shellfishing. If a wound is sustained, wash the area thoroughly with soap and water. The DoAg has prepared a Guidance Document for Recreational Shellfish Harvesting and Vibrio, and maintains a webpage on shellfish safety and handling. All shellfish must be immediately placed on ice in a cooler to prevent temperature abuse.
Prior to harvesting, always ensure you have the appropriate permits, know the areas that are certified for recreational shellfishing using maps, and call the hotline daily to hear the status (open/closed) of the areas before harvesting. Additional information about town recreational areas, maps, and hotlines is available on the DoAg website.
What else should I know about Connecticut's shellfish program and Vibrio?
From June-September, the DoAG tests Vibrio levels in commercial shellfish from statewide locations each month as part of the routine monitoring program. This routine testing is not required by the National Shellfish Sanitation Program, but is conducted by DoAg to protect public health. The DoAG laboratory uses an FDA-approved DNA-detection method to monitor for two Vibrio species, Vibrio parahaemolyticus and Vibrio vulnificus (learn more about the Bureau of Aquaculture Laboratory Services). The DoAG lab has been analyzing samples for Vibrio parahaemolyticus since 2013, and Vibrio vulnificus since 2022. The Vibrio vulnificus testing was added to the DoAG lab’s platform in 2022, partly in response to the five Vibrio vulnificus wound infections that occurred in 2020.
The routine Vibrio parahaemolyticus monitoring, annual Vibrio control plans, and illness investigations conducted nation-wide have demonstrated that CT has not had a Vibrio outbreak since the control plans were established in 2014. In collaboration with other state agencies, the DoAg routinely conducts illness investigations for all cases where Connecticut shellfish was on-hand when illnesses occurred. The national illness investigation program helps to protect public health by identifying illness outbreaks, identifying the source(s) of the illnesses, and removing implicated shellfish from the market.
While some states cultivate shellfish on intertidal mud flats that are exposed to extreme temperatures in the summer, all of the shellfish in CT is cultivated in deeper, offshore waters. This, combined with the Vibrio parahaemolyticus control plan requirements, prevents shellfish from being exposed to the sun and high temperatures while being harvested on commercial boats.
What are some common misconceptions about Vibrio in Connecticut?
One of the most common misconceptions about Vibrio is that it is an introduced pathogen due to contamination or new to the region due to warming water temperatures. Vibrio are not introduced, and have been present in Long Island Sound at least for decades. With the effective statewide controls in Connecticut, the number of Vibrio illnesses from shellfish consumption has not increased. An additional misconception is that Connecticut shellfish have been implicated in Vibrio vulnificus illnesses due to consumption. Connecticut shellfish have never been associated with Vibrio vulnificus infections.
Are there individuals who are more at risk of illness?
Because shellfish are consumed raw, certain individuals should always consult their physicians before consuming oysters or clams as they are more susceptible to food borne illnesses, including Vibrio. It is important to note that when shellfish are cooked, they are typically not cooked at a high enough temperature for long enough time to eliminate these risks. Individuals at a higher risk for foodborne illness when consuming shellfish include:
Pregnant individuals
Young children and older adults
Persons with compromised immune systems
Persons who are taking protein pump inhibitors and/or antacids
Who are the state agencies responsible for Vibrio?
Questions regarding Vibrio in shellfish should be directed to the CT DoAg (Agri.Aquaculture@ct.gov). Questions regarding Vibrio vulnificus wound infections should be directed to the CT Department of Public Health. Questions regarding bathing beaches should be directed to CT DEEP Beach Monitoring.