Part of the Communicable Disease Control Manual
Appendix reviewed and updated in March 2018. A description of changes can be found at Updates to the Communicable Disease Control Manual.
Although the terms ‘enteric’ and ‘food and waterborne’ illness are sometimes used interchangeably, not all enteric diseases are caused primarily by food or water. Conversely, some diseases that can be transmitted by food or water are not considered ‘enteric’. Most of the diseases covered in this appendix have – to a greater or lesser extent – an association with food or water, hence the terms ‘foodborne’ and ‘waterborne’ are used. Nevertheless, animal and farm environment contact should be considered important routes of infection in New Zealand.
In all cases of enteric illness, health services should refer to the specific disease chapters or the chapter on acute gastroenteritis in this manual and base the scope of their investigation on an assessment of the risk of disease spread. It is essential to obtain a clinical history of symptoms and exposure through possible food, water or animal contacts as well as through the case’s occupation. Whenever possible, arrangements should be made for appropriate specimen (s) to be sent for laboratory testing to confirm the diagnosis.
If a reported case is thought to be part of an outbreak, it is essential that health services follow the approach outlined in the Guidelines for the Investigation and Control of Disease Outbreaks (ESR 2012) to ensure the assessment of the possibility of shared risk factors in order to prevent further cases.
Food and waterborne illnesses are itemised in Section A of the list of notifiable diseases. They are therefore notifiable by the attending health practitioner and laboratories to a medical officer of health and by the attending health practitioner to the territorial authority (TA). This requirement for reporting to TAs can be fulfilled by summary reporting from the public health unit.
Roles and responsibilities
Liaison with the Ministry for Primary Industries (MPI) is required when food/food businesses are suspected of being the cause of illness. MPI is the New Zealand regulatory authority for food safety, including domestic food and imports and exports of food and food-related products. MPI is the lead agency for investigating, improving and promoting food safety and protecting consumers from risks (including nutrition and public health risks) that may arise in connection with the consumption of food.
Where food/food businesses are thought to be involved inform MPI. This includes commercially prepared food and recreationally gathered food.
Table 2.1 summarises responsibilities of public health units when investigating an outbreak of foodborne illness.
Common incubation periods for enteric disease are summarised in Table 2.2.
Mode of transmission
Most notifiable enteric diseases are transmitted to a greater or lesser extent by ingestion of contaminated food or water.
Nevertheless, person-to-person spread via the faecal-oral route is a particularly important route of transmission for norovirus, rotavirus, enteric adenovirus and Shigella. E. histolytica may also be transmitted person to person by the faecal-oral route. Norovirus may be transmitted by aerosol around infected vomit or faeces.
Period of communicability
For those diseases that have a significant degree of person-to-person transmission, periods of communicability are summarised in Table 2.3.
Cases of most enteric disease should be considered infectious and should remain off work/school until 48 hours after symptoms have ceased. Certain individuals pose a greater risk of spreading infection and additional restriction/exclusion criteria may apply. Microbiological clearance may be required for individuals infected with/exposed to certain pathogens.
The key criteria are:
- the decision to exclude any worker is based on individual risk assessment. As a general rule, any worker with symptoms of gastrointestinal infection (diarrhoea and/or vomiting) should remain off work until clinical recovery and stools have returned to normal (where the causative pathogen has not been identified). Where the pathogen has been identified, specific criteria are summarised in Table 2.4
- the overriding prerequisite for fitness to return to work is strict adherence to personal hygiene, whether symptomatic or not.
The circumstances of each case, carrier or contact should be considered and factors such as their type of employment, availability of toilet and hand washing facilities at work, school or institution and standards of personal hygiene taken into account. For example, a carrier may be relocated temporarily to a role that does not pose an infectious risk.
Pathogen specific exclusion criteria for people at increased risk of transmitting an infection to others
Pathogen specific exclusion (restricting criteria for people from work, school or an early childhood service and for subsequent clearance are summarised in Table 2.4. Additional information is also included in the table for the following groups:
- people whose work involves preparing or serving unwrapped food to be served raw or not subject to further heating (including visitors or contractors who could potentially affect food safety)
- staff, inpatients and residents of health care, residential care, social care or early childhood facilities whose activities increase risk of transferring infection via the faecal-oral route
- children under the age of 5 attending early childhood services/groups
- other adults or children at higher risk of spreading the infection due to illness or disability.
The Health (Infectious and Notifiable Diseases) Regulations 2016 do not contain any exclusionary powers or incubation periods for infectious children, or for high risk occupational groups such as people who work with children or food handlers. Instead the medical officers of health can resort to broader powers in Part 3A of the Health Act 1956, which include directions to cases and contacts to remain at home until no longer infectious. This Manual contains the recommended exclusion periods for specific diseases (Refer: Table 2.4).
There is guidance published about the 2016 regulations and Part 3A of the Health Act in Summary of Infectious Disease Management under the Health Act 1956. The legislation is principles based. In this context this means that medical officer of health must weigh protection of public health (the paramount consideration) with the following principles: trying voluntary means first if likely to be effective, choosing a proportionate, and the least restrictive measure required in the circumstances, fully informing the case or contact of the steps to be taken and clinical implications, treating them with dignity and respect for their bodily integrity and taking account of their special circumstances and vulnerabilities, and applying the measures no longer than is necessary (sections 92A to 92H).
Under Part 3A a medical officer of health can direct a case or a contact to stay home (section 92I(4)(b) or 92J(4)(b)). This is when the officer believes on reasonable grounds that the case or contact poses a public health risk (as defined in the s2 Act). The direction must specify duration.
Alternatively, in the context of attendance at an educational institution, if the officer believes the infection risk is unlikely to be effectively managed by directing the case or contact, he or she can approach the head and direct them to direct the case or contact to remain at home. In serious cases, the medical officer of health can also direct the head to close the institution or part of it (s 92L).
Medical officers of health have no powers to direct closure of premises or places where people congregate, other than educational institutions. If a medical officer of health needs to manage a public health risk by excluding infectious people from certain occupations, public pools, campsites, concerts and other public environments, he or she can use directions to the individuals concerned – to stay away from a certain place, or not to associate with certain people.
The Ministry for Primary Industries has powers to close commercial food premises. In contrast, medical officer of health powers focus on the risk the person poses.
Note that while there are provisions that apply to early childhood service workers, there are no provisions for health care workers – instead, advice should be provided to employers in terms of the Health and Safety at Work Act 2015.
Employers may decide to implement more stringent exclusion/restriction criteria in response to their own or their customers’ requirements.
In exceptional circumstances, eg, where workplace hygiene or sanitation is uncertain, a case may need to be excluded until they have submitted appropriate negative stool(s), taken at a suitable interval.
References and further information
- ESR. 2012. Guidelines for Investigating Communicable Disease Outbreaks. Porirua: Institute of Environmental Science & Research Limited.
- Heyman, D.L. 2015. Control of Communicable Disease Manual, 20th Edition. Washington: American Public Health Association.
- Communicable Disease Network Australia. 2010. Guidelines for the public health management of gastroenteritis outbreaks due to norovirus or suspected viral agents in Australia. Canberra: Department of Health and Ageing.
 Where food/food businesses are thought to be involved inform the Ministry for Primary Industries.