Authors: Holly Abeels, UF/IFAS Florida Sea Grant Extension; Gabby Barbarite, Harbor Branch Oceanographic Institute, FL Atlantic University; Betty Staugler, UF/IFAS Florida Sea Grant Extension; L Scott Jackson, UF/IFAS Florida Sea Grant Extension
Recent news headlines report another emergence of the bacteria Vibrio vulnificus and Vibrio parahaemolyticus. Recently, the term “flesh-eating bacteria” has been used to refer to Vibrio. This description is misleading and causes unnecessary fear and panic. Vibrio should not keep Floridians and visitors from enjoying their favorite activities because Vibrio infections are rare and simple actions can be taken to reduce risk.
Under certain conditions, Vibrio is capable of causing wound infections and seafood sickness in people. People can encounter Vibrio if they expose an open wound to the water through activities like fishing and swimming or if they eat raw oysters and other raw seafood. Be aware of the hazards and follow a few simple safety guidelines to ensure that your time on the water is as safe and enjoyable as possible.
Where and when are they found?
Vibrio naturally occur in coastal waters worldwide. They can be present in waters in Florida and elsewhere across the United States. Species that infect humans are most common in brackish environments — areas in which freshwater and saltwater mix. Contrary to popular belief, Vibrio vulnificus and Vibrio parahaemolyticus are typically found in estuaries and bays, rather than the beach or ocean because they can’t tolerate high salt levels. Though present in Florida waters year-round, Vibrio are most abundant from April to November, when temperatures are the warmest. These natural peaks correspond with an increase in human infections, which are usually highest during the summer months.
Who is at risk for infection?
Healthy people are usually not at risk for serious infection from raw shellfish consumption, but can develop cellulitis, an infection of the skin and deep underlying tissues, due to open wound exposure. However, people with weakened immune systems can develop life-threatening infections. Some high-risk conditions that increase susceptibility include liver disease, alcoholism, diabetes, hepatitis, hemochromatosis (iron overload), stomach disorders, HIV/AIDS, cancer, long-term steroid use, and those taking acid reflux or heartburn medications. Severe illness almost exclusively occurs in people who have these risk conditions. Though these cases are rare, they can be very serious and progress rapidly. Seek medical treatment immediately if you suspect infection. Consult with your doctor if you have questions about your risk.
The term “flesh-eating bacteria” has been used to refer to Vibrio. This description is misleading. These bacteria do not decompose healthy, intact skin, even if contacted for long periods of time. Infections are acquired when Vibrio encounter broken skin and open wounds or are consumed in large quantities via raw or contaminated seafood. Only when the bacteria enter the body through these processes are they capable of causing disease in certain individuals. Activities that may result in contact with these bacteria include fishing, wading and swimming as well as cleaning and eating seafood, especially during summer months.
Who monitors cases of Vibrio?
State health departments report cases to the U.S. Centers for Disease Control and Prevention (CDC) through a surveillance system. However, because Vibrio bacteria are not easily identified with routine testing, many cases are not reported.
Looking locally: Florida cases
Sixty-seven percent of U.S. cases are reported from the Gulf and Atlantic coastal regions due to water parameters suitable for Vibrio as well as activities like seafood harvest and marine recreation. This is especially true for Florida, which has the highest national incidence of vibriosis, the name of this disease. Over the last decade (2008-2017), the state reported an average of 165 cases a year. In 2017, the vibriosis rate increased notably to 274 reports; of those, Vibrio vulnificus was responsible for 50 infections and 11 deaths, Vibrio parahaemolyticus caused 37 infections. Five Vibrio vulnificus cases were associated with Hurricane Irma in 2017, with each reporting wound exposure to either floodwaters or debris from the hurricane. So far this year (2019), there have been 10 confirmed cases of Vibrio vulnificus in Florida.
Between 2004 and 2017, 52.8% of Vibrio vulnificus cases were attributed to wound infections. Seafood exposures accounted for 22.3% of reported cases and the remaining 24.9% had undetermined exposures.
This may seem alarming at first, but infections are quite rare considering the millions of people that participate in water activities and consume local seafood each year. In fact, only a small percent of the population is classified as high risk for developing infection.
Vibrio bacterium can enter through a new wound or through an existing wound, like a tiny cut, scratch or even a mosquito bite. For most healthy individuals, any infection or irritation is minor and hardly noticed. However, for people who have weakened immune systems, risk of infection is much higher. Vibrio wound infections happen fast; symptoms may become evident in only 4 hours.
Hazards associated with Vibrio-related wound infections are greatest:
- In stagnant, inshore waters and during warm, rainy months due to high natural abundances
- When a wound is submerged for a long period of time or an injury goes untreated
- For individuals with weakened immune systems or underlying disease
Infections typically begin with swelling and redness of skin, followed by severe pain, blistering, and discharge at the site of the wound. As the infection progresses, tissue necrosis, fever, chills, low blood pressure, shock, and death may occur, especially if it spreads to the bloodstream. Symptoms may arise within 1 to 3 days, but usually occur a few hours after exposure. Disease can progress rapidly and recovery is greatest when diagnosed early. Infections can not heal on their own and require medical treatment.
Recommendations for avoiding wound infections
It is important to understand your personal risk for developing infection, which may be different from others around you. Be prepared and ensure that you have access to a first aid kit when spending a day on the water. If you are out on the water and cut yourself, use appropriate first aid and wound care. Remember, the best way to avoid infection is to prevent exposure in the first place!
First aid and wound care
- Wash the wound thoroughly with soapy water and remove any foreign material
- Follow with rubbing alcohol or peroxide, antibiotic ointment, and cover with a bandage
- Avoid further contact with the environment and keep the area clean until it has healed
While most people are not susceptible to infection by Vibrio, individuals who have certain illnesses or health conditions (described already) should only eat seafood that is cooked and abstain from eating it raw or partially cooked.
- During the summer months, especially in coastal areas due to high natural abundances
- When consuming raw, undercooked, or contaminated cooked seafood – especially shellfish and specifically raw oysters
- For Individuals with weakened immune systems or underlying disease
Symptoms and disease
Anyone who eats raw or improperly cooked seafood is susceptible to infection by Vibrio. The severity of disease depends on the amount of pathogenic bacteria consumed as well as the individual’s health. Symptoms include watery and/or bloody diarrhea, nausea, vomiting, abdominal cramps, headache, fever, and chills. Symptoms can occur anywhere from 4 to 36 hours after consumption but generally start after about 15 hours. Illnesses typically last for 2 to 6 days; some are self-limiting and heal on their own over time, while those that are more severe can be treated with antibiotics. Most healthy people are not at risk of serious infection and will generally have mild symptoms. In individuals with weakened immune systems disease can be severe or fatal if the infection spreads to the blood (causing septicemia or sepsis). Seek medical attention immediately if you have consumed raw shellfish and have any of these symptoms, especially if you are in a high-risk group.
Recommendations for avoiding infections
Infections can be prevented by cooking seafood properly, avoiding cross contamination of raw seafood with cookware, utensils, or other food, and by consuming cooked seafood. Food should be heated to at least 145°F (internal temperature) for at least 15 seconds. Keep raw foods from coming into contact with cooked foods and surfaces that are used for eating. Thoroughly wash utensils, dishes, surfaces, hands, etc. that contact raw food with hot water and soap before they are used again. Keep food refrigerated at or below 40°F and quickly refrigerate cooked food if it’ll be stored for later.
Tips for fishing, shellfish harvesting, or handling traps
- When fishing, harvesting shellfish, or handling traps, use caution and wear gloves where practical to prevent wounds. Treat new wounds quickly using first-aid and wound care described previously.
- Wear protective coverings on your feet and, in general, use caution when in and around coastal waters.
- Fish (including live bait), crabs and shellfish can carry Vibrio. Use caution when hooking or handling, paying attention to areas that can inflict injuries like spines, shells, and claws, barbs, and teeth.
- Always wash your hands thoroughly after participating in these activities, especially before handling food.
- Be sure to clean your gear after each use, taking special care with sharp objects like hooks and knives.
- Bait buckets, live wells, and holding boxes can be reservoirs for Vibrio because they accumulate bacteria from the waste produced by animals inside. Use care to avoid exposing wounds.
Impacts from climate change
There are some scientific studies that indicate as global temperatures rise, the season for potential infections is being extended. This means more cases are being reported outside of the typical warm-weather months. This is particularly important in areas where shellfish are harvested since in many places harvesting occurs in the fall, winter, and spring when temperatures aren’t favorable for Vibrio to grow. Also, Vibrio species are being seen geographically in areas where they were previously rarely or not reported. As sea levels rise, the saltwater will penetrate further upstream into freshwater creating conditions that are more favorable to Vibrio in the future.
Some final thoughts and advice
- Remember that most healthy individuals will not have any problems.
- If you are recovering from illness, know your limits and use the above resources to make informed decisions to protect your health.
- If you have any question about your risk, consult with your doctor.
- Plan your day on the water or at the beach for safety. Then confidently relax and enjoy the experience.
Helpful resources and links:
Frequently Asked Questions About Vibrio in Florida Factsheets:
Florida Health Department:
Centers for Disease Control:
Georgia Sea Grant: Safe Oysters:
Vibrio Research and Practical Information:
Florida Department of Agriculture and Consumer Services – Eating Oysters: A Health Advisory FAQ: