Vibrio parahaemolyticus Infection

Etiology

First discovered in the 1950s in Japan, V. parahaemolyticus is a gram-negative bacterium found in marine and estuarine environments. It is associated with the consumption of raw seafood, especially shellfish such as mussels. V. parahaemolyticus thrive in warmer water and areas of less salinity.[3]

Epidemiology

Although a major cause of gastroenteritis in Japan, V. parahaemolyticus gastroenteritis is less common in the United States with the Center for Disease Control reporting a 2016 incidence of 0.45 cases per 100,000. The incidence in the United States has been steadily increasing. There are typically more cases during the warmer months (May through October), and cases commonly occur as part of an outbreak. Even though V. parahaemolyticus grows best in warmer waters, outbreaks have been reported in colder areas such as Alaska. Despite being found freely in saltwater, it can be found in higher concentrations in shellfish such as mussels, since they filter the water concentrating the bacteria.[4]

Pathophysiology

V. parahaemolyticus can infect the host through different routes. Infected seafood can be consumed, causing direct contact with the gastrointestinal system. The bacteria can also make their way into an open wound during exposure to saltwater. In severe cases and those with comorbidities, once inside the host the bacteria can further spread into the blood. V. parahaemolyticus has several virulence factors common to other bacteria. However, the major virulence factor of V. parahaemolyticus is thermostable direct hemolysin (TDH). TDH is present in the majority of clinical specimens (88% to 96%) but only in approximately 1% of natural populations of V. parahaemolyticus. Despite this fact, TDH has been identified as a major virulence factor, the specific mechanism by which TDH causes gastroenteritis is not completely understood. TDH is a pore-forming toxin, and researchers postulate that this could be related to its ability to cause gastrointestinal symptoms. In addition to the TDH virulence factor, V. parahaemolyticus also uses a type 3 secretion system, similar to other gram-negative bacteria. Despite its virulence factors, the majority of V. parahaemolyticus infections only result in self-limiting enteritis.

History and Physical

A detailed history is vital to a timely and successful diagnosis of a V. parahaemolyticus infection. Patients will typically present with gastroenteritis-type symptoms such as abdominal cramping, nausea, vomiting, and fever. Because these are general symptoms common to many other illnesses, the line of questioning should include any recent travel to or near the ocean or any consumption of shellfish or seafood, especially raw oysters. This condition is more common in coastal cities, but there are several cases of V. parahaemolyticus in areas distant from the sea. This is a result of patients developing symptoms after returning home from recent travel. The average time from consumption of contaminated food to the onset of symptoms is 17 hours.

In addition to asking about specific V. parahaemolyticus risk factors, information regarding relevant comorbidities should be elicited. Patients who develop an infection with concomitant liver disease, diabetes, or alcoholism have a poorer prognosis and are more likely to develop septicemia.

Physical findings are also generalized. On exam, patients may present with signs of dehydration, non-specific abdominal pain, and occasional bloody stool (approximately 7%). Be alert for signs of cellulitis, especially on body areas exposed to the water such as feet and lower legs. The examination should include a careful review of vital signs for assessment of sepsis. Due to its non-specific findings, the diagnosis is difficult to make on physical exam alone. A detailed and thorough history is essential to raising suspicion and ultimately making a diagnosis of V. parahaemolyticus.

Evaluation

For a patient with a suspected V. parahaemolyticus infection, the diagnostic method of choice is obtaining a stool culture. It is best to choose a selective medium for culture. V. parahaemolyticus grows particularly well on Thiosulfate Citrate Bile-salts Sucrose (TCBS). The bacteria can also demonstrate hemolysis as well as urease positivity. The provider should contact the laboratory and discuss suspicion for V. parahaemolyticus as this can help the lab utilize specialized techniques that can enhance the chance for successful growth. If there is suspicion of septicemia or wound infection, blood and wound cultures can also be obtained.[5]

Treatment / Management

Treatment for the majority of cases is supportive, the same as for most other causes of gastroenteritis. Appropriate initial steps include intravenous fluid rehydration and correction of electrolyte abnormalities. The typical course of infection is self-limited and in most cases does not require additional treatment. There are no recommendations for using antimotility agents to treat diarrhea. In more severe cases such as wound infections and sepsis, antibiotic treatment is indicated. There have been no large studies involving antibiotic treatment specifically for V. parahaemolyticus infection. The recommendations are based on guidelines from studies examining treatment for other Vibrio species. If the patient has a particularly severe case of gastroenteritis, doxycycline is the antibiotic of choice. For uncomplicated wound infections, treat with minocycline or doxycycline. Consider adding a third-generation cephalosporin if the wound infection is severe or if the patient is at significant risk for sepsis (has underlying liver disease, alcohol use disorder, or has diabetes mellitus). For severe cases, the patient should be admitted to the hospital for further intravenous fluid replacement and infectious disease consultation. Mild cases, with a hemodynamically stable patient, can be treated and observed in the emergency department. If the patient remains stable and does not have any signs of sepsis, they may be discharged.[6]

Prevention of V. parahaemolyticus infection is similar to other food-borne illnesses. Seafood should be stored properly and appropriately cooked before consumption. The Center for Disease Control and Prevention recommends against consuming raw oysters or other shellfish, especially in at-risk populations. Additionally, people with open wounds should avoid exposure to brackish or saltwater.

Differential Diagnosis

• Bacterial gastroenteritis
• Cholera
• Toxic shock syndrome
• Necrotizing fasciitis

Complications

• Compartment syndrome
• Reactive arthritis
• Shock
• DIC
• Multiorgan failure