Vibrio Parahaemolyticus Infection

Vibrio parahaemolyticus is a halophilic Gram-negative bacillus of warm coastal and estuarine waters, and a common cause of seafood associated gastroenteritis.

• Infection follows raw or undercooked shellfish, crustaceans and fish; it also causes wound infections after marine exposure.
• Illness peaks in warm months and in coastal regions; the Kenyan coast carries risk.
• Pathogenic strains carry thermostable direct haemolysin and related haemolysin genes.

Incubation 12 to 24 hours (range 4 to 96).

• Watery diarrhoea, abdominal cramps, nausea, vomiting, fever and chills, lasting about 3 days; occasional bloody stool.
• Wound infection: cellulitis, bullae, necrotising soft tissue infection in the immunosuppressed.
• Differential diagnosis: cholera, V vulnificus infection, Salmonella, Staphylococcus aureus or Bacillus cereus food poisoning, norovirus, ETEC, scombroid poisoning.
• Complications: dehydration, septicaemia (cirrhosis, haemochromatosis, diabetes, immunosuppression), necrotising fasciitis, limb loss and death.

Stool and wound culture on thiosulfate citrate bile salts sucrose agar (green colonies); alert the laboratory to seafood exposure.

• Blood cultures in febrile or immunocompromised patients.
• Full blood count, electrolytes, creatinine, liver profile, lactate; imaging for deep infection.

Supportive: oral rehydration with low osmolarity solution; intravenous Ringer lactate for severe dehydration; most illness is self limited within 3 days.

Pharmacological

• Moderate to severe gastroenteritis or immunosuppression: doxycycline 100 mg twice daily for 3 days, or ciprofloxacin 500 mg twice daily for 3 days, or azithromycin 500 mg once daily for 3 days.
• Wound infection and septicaemia: doxycycline 100 mg IV or oral twice daily plus ceftazidime 1 to 2 g IV every 8 hours (or ceftriaxone 2 g IV daily), for 7 to 14 days.
• Children: azithromycin 10 mg/kg once daily for 3 days; avoid doxycycline under 8 years unless the benefit is clear.

Procedures: early surgical debridement and fasciotomy for necrotising infection.

Special groups: cirrhosis and iron overload (high mortality, prompt antibiotics); pregnancy (azithromycin).

Red flags: septic shock, haemorrhagic bullae, rapidly spreading cellulitis, bloody diarrhoea with systemic toxicity.

Follow-up: wound review at 48 hours; advise cooking seafood thoroughly, refrigeration at 4 C or less, avoid raw shellfish with liver disease.