Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | International measures

Victorian statutory requirement

Salmonellosis (Group B disease) must be notified in writing within five days of diagnosis.

Laboratories are required to notify Salmonellae isolated from food or water.

School exclusion: exclude cases from child care and school until after the diarrhoea has ceased.

Infectious agent

Approximately 2000 known serotypes exist of Salmonella spp, a small number of which usually account for the majority of infections.

Identification

Clinical features
Salmonellosis commonly presents as an acute gastroenteritis with fever, vomiting, nausea, abdominal pain, headache and diarrhoea. Dehydration may occur, especially among infants and the elderly. Infection may also present as septicaemia and occasionally may be localised in other body tissues resulting in endocarditis, pneumonia, septic arthritis, cholecystitis and abscesses. Symptoms usually last three to five days.

Method of diagnosis
Infection is diagnosed by isolation of Salmonella spp. from faeces, blood or other clinical specimen.

Incubation period

The incubation period is usually 6–72 hours with an average of 12–36 hours.

Public health significance & occurrence

Salmonella infection occurs worldwide and only a small proportion of cases are detected and reported. The incidence of infection is highest in infants and young children. Mortality is low however it may be increased in the elderly and immunocompromised people.

almonellosis may incur significant social and economic costs due to lost productivity and the impact on industry and agriculture.

There are approximately 1000 cases of salmonellosis reported in Victoria each year. The most common serovar is S. typhimurium. The majority of cases are sporadic, but outbreaks in institutions and child care centres and those associated with retail food premises are not uncommon. The emergence of strains resistant to single or multiple antibiotics is of increasing concern worldwide.

Reservoir

Domestic and wild animals including poultry and reptiles act as reservoirs. Patients and convalescent carriers including mild and unrecognised cases can also act as reservoirs.

Mode of transmission

Transmission is via person to person or animal to person spread via the faecal-oral route.
Ingestion of the organisms via contaminated or improperly cooked foods also occurs. This occurs particularly with:

• raw and undercooked eggs and egg products
• raw milk and raw milk products
• poultry and poultry products
• raw red meats
• unwashed salads, fruits and vegetables, grains, seeds and nuts
• some shellfish and filter feeders such as oysters

Period of communicability

Salmonellosis is communicable through the course of infection, usually several days to several weeks. One per cent of infected adults and five per cent of children under the age of five years excrete the organism for more than one year. Antibiotics given in the acute illness can prolong the carrier state.

Susceptibility & resistance

Susceptibility may be increased by some medical conditions and treatments including immunosuppressant therapy, prior or concurrent broad-spectrum antibiotic therapy, gastrointestinal surgery, antacid use, achlorhydria and malnutrition.

Severity of the disease varies with:

• the serotype
• the numbers of organisms ingested
• the vehicle of transmission
• host factors.

Control measures

Preventive measures
Thoroughly cook all food derived from animals sources, particularly poultry, pork, egg products and meat dishes. Inadequate temperature control and incorrect storage of food during and after the cooking process facilitates bacterial multiplication and are important risk factors.

• Avoid recontamination from raw food within the kitchen or refrigerator, after cooking is completed.
• Emphasise the importance of refrigerating food and maintaining a sanitary kitchen.
• Avoid consuming raw or incompletely cooked eggs, or using dirty or cracked eggs.
• Pasteurise all milk and egg products.
• Educate food handlers on the importance of hand washing and separating raw and cooked foods.
• Inspect and supervise abattoirs, butcher shops, food-processing plants and egg-grading stations.

Control of case
Treatment is supportive and antibiotics are not indicated in uncomplicated gastroenteritis as they may prolong the carrier state and promote antibiotic resistance. The exceptions are patients at high risk of more severe disease including infants under two months of age, the elderly and immunocompromised (particularly those with HIV), and food handlers who are chronic carriers. For systemic disease, the choice of antibiotic should be based on the antibiograms of the relevant serovar and local antibiotic guidelines.

Use standard enteric precautions when handling faeces, contaminated clothing and bed linen from hospitalised patients.

Exclude symptomatic cases from food handling and direct care of children, the elderly and immunosuppressed patients until after the diarrhoea has ceased. Children are excluded from school and child care until diarrhoea has ceased.

Instruct asymptomatic individuals in strict personal hygiene. Stress proper hand washing.

Control of contacts
Consider the diagnosis in symptomatic contacts. Active case finding is not routinely undertaken in sporadic cases.

Control of environment
Sources of contamination such as use of uncooked products and inadequate cooking should be investigated. Attention should be paid to environmental cleaning, particularly in institutions, child care centres and food premises.

Outbreak measures

Two or more related cases of gastroenteritis are suggestive of an outbreak and should be reported to the Department of Human Services immediately. The aims of an outbreak investigation are to rapidly identify the source and prevent further cases. Epidemiological, environmental and laboratory investigations will be implemented immediately.

Stools should be collected from cases and attempts made to identify a common source by obtaining food histories and potentially relevant environmental exposures. Any implicated foods should be retained for analysis at the Microbiological Diagnostic Laboratory. Staff of the Communicable Diseases Section, the Department’s Food Safety Unit, and Local Government Environmental Health Units usually conduct environmental investigations.

Refer to the Department’s Guidelines for the investigation of gastrointestinal illness for specific details.

International measures

International outbreaks are increasingly being recognised, primarily due to the increased dissemination of food and agricultural products worldwide. Investigation of imported products should be coordinated through Food Standards Australia New Zealand.