Infectious diseasesepidemiology and surveillance

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 | Additional sources of information

Victorian statutory requirement

Isolated cases are not notifiable.

School exclusion: exclude from school or childcare centres until after symptoms have ceased or a medical certificate of recovery is produced.

Infectious agents

Small round structured viruses (SRSVs) including noroviruses and other caliciviruses, astroviruses and adenoviruses are the infective agents.

Identification

Clinical features
Illness is characterised by an acute onset of fever, myalgia, headache, nausea, vomiting, abdominal cramps and watery diarrhoea lasting 12–60 hours. Vomiting is relatively more prevalent among children. Forceful vomiting as a predominant symptom and a significant secondary attack rate in an outbreak of gastroenteritis are suggestive of norovirus infection. Although rare, severe dehydration caused by viral gastroenteritis can be fatal in persons with debilitating health conditions.

Method of diagnosis
Diagnosis is predominantly based on clinical presentation. Virus in stool can be visualised and distinguished by electron microscopy. Nucleic acid hybridisation assays and RT-PCR assays to detect norovirus genome are a sensitive and specific tool for outbreak investigations. Nucleotide sequencing provides a classification of the viruses n observed,and is an important tool in establishing links to contaminated vehicles of infection in outbreak settings.

Incubation period

The incubation period is usually 24–48 hours. The known range for norovirus is 10–50 hours.

Public health significance & occurrence

The endemic burden of gastroenteritis of viral causes is not known however norovirus is recognised as the major cause of outbreaks of non-bacterial gastroenteritis. Explosive outbreaks have occurred in institutions, camps, childcare centres, cruise ships, restaurants and following catered functions. Approximately 50% of gastroenteritis outbreaks investigated each year in Victoria are attributed to viral pathogens. High secondary attack rates result in outbreaks that are often prolonged and difficult to contain.

Disease occurs in all age groups and predominantly affects infants and young children. In Australia, viruses can be detected throughout the year but are more common in the period from late winter to early summer. Norovirus has been reported to account for between 5–17% of cases of diarrhoea in the community and 5–7% of cases requiring treatment by physicians.

Reservoir

The reservoir is thought to be primarily humans.

Mode of transmission

Viral gastroenteritis is predominantly spread via the faecal-oral route. Transmission is facilitated through contaminated food (particularly raw shellfish), water (including ice) and person to person contact. Aerosols are thought to be important in the transmission of norovirus and it is also known to persist on certain contaminated surfaces such as carpets for weeks.

Period of communicability

Communicability continues during the acute phase and for as long as viral shedding persists. Cases should be considered infectious until at least 48 hours after diarrhoea has ceased. Shedding of norovirus in the absence of clinical illness can persist for up to two weeks and is of concern in food-handler related transmission.

Susceptibility & resistance

Everyone is susceptible to infection and infection is not known to confer lifelong immunity.

Control measures

Preventive measures
Prevention is dependent on attention to good food and personal hygiene, particularly hand washing.

Control of case
Treatment is symptomatic and should be focussed on maintaining hydration.

Healthcare workers and food handlers should be excluded from work until at least 48 hours after diarrhoea and vomiting has ceased. Children should be excluded from school or childcare centres until after symptoms have ceased or a medical certificate of recovery is produced. Residents of institutions should be isolated until diarrhoea has ceased.

Control of contacts
Advise case to maintain strict personal hygiene and hand washing in the home.
Determine if others are ill. If so, report to Local Government environmental health officers or the Department’s Communicable Diseases Section so that outbreak investigation and control can occur.

Control of environment
The ability of norovirus to survive relatively high levels of chlorine and varying temperatures (from freezing to 60°C) means rigorous attention to clean-up procedures and personal and home hygiene is essential in preventing further transmission.

Outbreak measures

An outbreak is defined as two or more related cases of gastroenteritis. The primary aim is to prevent further disease by identifying the source, cleaning contaminated environments and isolating cases.

Special settings
Specific protocols for the management of outbreaks in special settings are available from the Communicable Diseases Section of the Department of Health.

Additional sources of information

Centres for Disease Control and Prevention 2001, ‘Norwalk-like viruses: public health consequences and outbreak management’, MMWR, vol. 50, RR9, pp. 1–18.