Chapter reviewed and updated in December 2017. A description of changes can be found at Updates to the Communicable Disease Control Manual.
New Zealand Epidemiology
Note: There are separate chapters for typhoid and paratyphoid fevers.
Common routes of infection in New Zealand for salmonellosis are via food, water, animal contact and exposure to the farm environment, and outbreaks are common. The highest rate of disease is reported in young children.
More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.
Further information on foodborne illness is available on the Ministry for Primary Industries website.
Salmonellosis presents as gastroenteritis, with abdominal pains, diarrhoea (occasionally bloody), fever, nausea and vomiting. Asymptomatic infections may occur and symptoms are not necessary to meet the case definition.
Laboratory test for diagnosis
Laboratory definitive evidence for a confirmed case requires identification of Salmonella species from a clinical specimen by one of the following methods:
- isolation (culture)
- detection of Salmonella nucleic acid.
Where possible culture should be attempted to facilitate serological or molecular typing to inform epidemiological investigations.
All isolates should be referred to the Enteric Reference Laboratory at ESR for further characterisation.
- Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
- Probable: A clinically compatible illness that either is a contact of a confirmed case of the same disease or has had contact with the same common source as a confirmed case – that is, is part of a common-source outbreak.
- Confirmed: A clinically compatible illness accompanied by laboratory definitive evidence.
- Not a case: A case that has been investigated and subsequently found not to meet the case definition.
Spread of infection
Domestic and wild animals including birds especially poultry, reptiles, amphibians, pigs, cattle, rodent and pets; also humans.
6–72 hours, commonly 12–36 hours.
Mode of transmission
Ingestion of organisms in contaminated foodstuffs, including meat products and imported foodstuffs. Many animals and birds are asymptomatic carriers of Salmonella spp. Undercooking of contaminated foodstuffs and cross-contamination (especially of raw fruits and vegetables) in the kitchen are thought to be responsible for many cases. Ingestion of faecally contaminated water causes frequent cases in New Zealand.
Infection may be a result of direct contact with an infected farm or domestic animal. Person-to-person spread is possible, notably from infants and stool-incontinent adults. Commonly reported risk factors identified in New Zealand cases include consuming food from retail premises, contact with animals (farm animals and pets, including fish and reptiles), consumption of untreated water and overseas travel. Recreational water contact and contact with symptomatic people during the incubation period are less commonly reported.
Period of communicability
Variable; typically several days to several weeks. Approximately 1 percent of infected adults and 5 percent of infected children under 5 years of age excrete Salmonella spp. for more than 1 year.
Attending medical practitioners or laboratories must immediately notify the local medical officer of health of probable or confirmed cases including asymptomatic cases when identified.
All health care workers are encouraged to talk with a medical officer of health about any suspected outbreaks of acute gastroenteritis or cases in people working in high-risk occupations.
Management of case
Obtain a food history and details of water consumption, animal contact and travel as well as details of occupation.
Investigate and obtain a more detailed history (using the ESR Salmonella questionnaire) if there is an outbreak or the case is in a high-risk occupation or attends an early childhood service.
Ensure symptomatic cases submit stool samples for testing.
In a health care facility, only standard precautions are indicated in most cases; if the case is diapered or incontinent, apply contact precautions for the duration of the illness. For further details, refer to the exclusion and clearance criteria in Appendix 2: Enteric disease.
Advise the case and/or caregivers of the nature of the infection and its mode of transmission. Educate about hygiene, especially hand cleaning.
Other control measures
Identification of source
Check for other cases in the community. Investigate potential food or water sources of infection only if there is a cluster of cases or an apparent epidemiological link.
If indicated, check water supply for microbiological contamination and compliance with the latest New Zealand drinking-water standards (Ministry of Health 2008). If a water supply is involved, liaise with the local territorial authority to inform the public. Advise on the need to boil water.
Clean and disinfect surfaces and articles soiled with stool. For further details, refer to Appendix 1: Disinfection.
Educate the public about safe food preparation (see Appendix 3: Patient information).
Hand-cleaning facilities should be available and used after contact with animals. Young children should be supervised during contact with animals and during hand cleaning. Food-related activities should be separated from areas that house animals. Domestic animals with diarrhoea should be taken to a veterinarian for assessment and treatment.
In early childhood services or other institutional situations, ensure satisfactory facilities and practices regarding hand cleaning; nappy changing; toilet use and toilet training; preparation and handling of food; and cleaning of sleeping areas, toys and other surfaces.
Ensure complete case information is entered into EpiSurv.
If a cluster of cases occurs, contact 0800GETMOH - CD option, and outbreak liaison staff at ESR, and complete the Outbreak Report Form.
Where food/food businesses are thought to be involved inform the Ministry for Primary Industries.
- Ministry of Health. 2008. Drinking-water Standards for New Zealand 2005 (Revised 2008). Wellington: Ministry of Health.