Notification requirement for salmonellosis
Salmonellosis (Group B disease) must be notified in writing within 5 days of diagnosis. This excludes typhoid and paratyphoid, which are Group A diseases.
Laboratories are required to notify Salmonella spp. isolated from food or detected in drinking water.
These are Victorian statutory requirements.
School exclusion for salmonellosis
Exclude cases from childcare and school until there has not been a loose bowel motion for 24 hours.
Infectious agent of salmonellosis
Approximately 2,000 known serotypes exist of Salmonella spp., a small number of which usually account for the majority of infections.
Identification of salmonellosis
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 3–5 days.
Infection is diagnosed by isolation of Salmonella spp. from faeces, blood or other clinical specimens.
Incubation period of Salmonella
The incubation period is usually 6–72 hours, with an average of 12–36 hours.
Public health significance and occurrence of salmonellosis
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, but may be greater in the elderly and immunocompromised people.
Salmonellosis may incur significant social and economic costs as a result of lost productivity, and impacts on industry and agriculture.
Approximately 2,000 cases of salmonellosis are reported in Victoria each year. The most common serovar is S. typhimurium. The majority of cases are sporadic, but outbreaks in institutions and childcare centres, and associated with retail food premises are not uncommon. The emergence of strains resistant to single or multiple antibiotics is of increasing concern worldwide.
Reservoir of Salmonella
Domestic and wild animals, including poultry and reptiles, act as reservoirs. Cases and convalescent carriers, including mild and unrecognised cases, can also act as reservoirs.
Mode of transmission of Salmonella
Transmission is usually person-to-person or animal-to-person via the faecal–oral route, through ingestion of the organisms via contaminated or improperly cooked foods. Foodborne transmission 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 of salmonellosis
Salmonellosis is communicable through the course of infection, usually several days to several weeks. One per cent of infected adults and 5 per cent of children under the age of 5 years excrete the organism for more than one year. Antibiotics given in the acute illness can prolong the carrier state.
Susceptibility and resistance to salmonellosis
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 for salmonellosis
Thoroughly cook all food derived from animals sources, particularly poultry, pork, eggs and egg products, and other meat dishes. Inadequate temperature control, and incorrect storage of food during and after the cooking process facilitate 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 handwashing, and separating raw and cooked foods.
Control of case
Treatment is supportive, and antibiotics are not indicated in uncomplicated gastroenteritis because they may prolong the carrier state and promote antibiotic resistance. The exceptions are patients at high risk of more severe disease, including infants under 2 months of age, the elderly, immunocompromised people (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 contact 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 childcare until there has not been a loose bowel motion for 24 hours.
Instruct asymptomatic individuals in strict personal hygiene, especially proper handwashing.
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, childcare centres and food premises.
Outbreak measures for salmonellosis
Two or more related cases of gastroenteritis are suggestive of an outbreak and should be reported to the department 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 at the Peter Doherty Institute. Staff of the department conduct environmental investigations, usually in conjunction with local councils.
Refer to the department’s Guidelines for the investigation of gastrointestinal illness for specific details.
International outbreaks are increasingly being recognised, primarily due to the increased dissemination of food and agricultural products worldwide. Investigation of imported products is coordinated through Food Standards Australia New Zealand.