Veterinary Epidemiology and Zoonosis

STAPHYLOCOCCAL FOOD POISONING

Synonyms

• Staphylococcal gastroenteritis, Staphylococcal toxicosis

Type of zoonosis

• Direct anthropozoonosis, Food-borne zoonosis

Definition

• Staphylococcal food poisoning is a gastrointestinal illness and vomiting, caused by eating foods contaminated with toxins produced by Staphylococcus aureus.

Etiology

• It is caused by enterotoxigenic Staphylococcus aureus.
• Staphylococcus spp. are Gram positive coccus (grape-like clusters / bunch of grapes) and facultative anaerobes.
• Enterotoxins are produced by coagulase-positive strains and very few coagulase-negative stains of Staphylococcus aureus.
• The contaminated food contains preformed toxins.
• Six types of enterotoxins have been identified till date, are A, B, C, D, E and F.
• Outbreaks are very common with enterotoxin A.
• Toxic shock syndrome (TSS) is due to enterotoxin F.
• The toxins are heat-resistant and can withstand a temperature of 100°C for 30 minutes.
• Staphylococcus spp. are salt tolerant and can grow in salty foods like ham. Examples of foods that have caused staphylococcal food poisoning are sliced meat, puddings, some pastries and sandwiches.
• Staphylococcal enterotoxin B is a bio-weapon.

Reservoir and incidence

• Staphylococcal food poisoning is common though out the world.
• The principle reservoir is the human carrier.
• Most of the healthy humans have staphylococci in the nasopharynx, thus contaminate the food materials while handling through sneezing and coughing.
• Infected cows, fowls and dogs may be a source of staphylococcal food poisoning in man.
• Human strains of Staphylococcus spp. are responsible for most of the outbreaks.
• Staphylococcus spp. vey well survive and multiply in meat, ham, milk, cheese, cream and ice cream.
• Milk pasteurization offers no guarantee of safety if toxins were produced before heat treatment, as the toxins are heat-resistant.
• Powdered milk replacement in the market serve as the good source for human infection.
• Staphylococcal enterotoxin B could be used as a biological weapon either by contamination of food/water or by aerosolization. The low inhaled dose chacterized by fever, cough, difficulty breathing, headache and some vomiting and nausea.

Transmission

• Ingestion of foods of animal origin is the chief way of transmission.
• Ingestion of milk and milk products from infected cows.
• Ingestion of contaminated eggs.

Disease in animals

• Mastitis in cattle.
• Pyoderma, impetigo, folliculitis and furunculosis in dogs.
• Salpingitis and arthritis in poultry.

Disease in humans

• The incubation period is short (~3 hours) and the course of the disease is usually benign and the patient recovers without medication in 24 to 72 hours.
• The start of clinical signs and severity of infection is depending on the quantity of pre-formed toxin in the food ingested.
• The major symptoms are pyrexia (38ºC), nausea, vomiting, abdominal pains and diarrhoea.
• More serious cases manifest prostration, cephalalgia, abnormal temperature and lowered blood pressure, as well as blood and mucus in the stool and vomit.
• Toxic shock syndrome: Symptoms consist of vomiting, diarrhoea, high fever, renal insufficiency and toxic shock. This syndrome had been very often noticed in women who become ill during their menstrual period.

Diagnosis

• Culture (Baird Parker medium) and identification from blood, vomitus, faeces and suspected food materials.

Treatment

• Symptomatic treatment consists of replacement of fluids and electrolytes.
• Antibiotic (Ciprofloxacin - 500 mg every 12 hours for 5 days) can be given if necessary.

Prevention and control

• Public health awareness to food handlers about food hygiene.
• Prevention of contamination of food with Staphylococcus spp. before the toxin is produced.
• Thorough washing of hands and under fingernails vigorously with soap and water before handling and preparing food.
• Do not prepare food if you have a nose or eye infection.
• Do not prepare or serve food for others if you have wounds or skin infections on your hands or wrists.
• Keep kitchens and food-serving areas clean and sanitized.
• If food is to be stored longer than two hours, keep hot foods hot (over 50°C) and cold foods cold (-2°C or under).
• Staphylococcal toxins are resistant to heat and cannot be destroyed by cooking.