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

Victorian statutory requirement

Clostridium botulinum infection (Group A disease) must be notified immediately by telephone or fax followed by written notification within five days.

School exclusion is not required.

Infectious agent

Clostridium botulinum is a spore-forming anaerobic bacillus. Several serotypes exist, however types A, B and E cause most human disease.

Identification

Clinical features
There are three forms of botulism:

• Classical botulism is a severe and often fatal infection resulting from ingestion of contaminated food. Symptoms include double vision, dysphagia and dry mouth. It can be followed by descending flaccid paralysis which may be associated with respiratory paralysis and result in death. Fever is absent unless a complicating infection occurs.
• Intestinal botulism is the most common form and usually affects infants under one year of age. It can affect adults who have altered gastrointestinal anatomy and microflora. The illness typically begins with constipation followed by lethargy, listlessness, poor feeding, ptosis, difficulty in swallowing and generalised muscle weak-ness (‘floppy baby’).
• Wound botulism is rare but has been seen after contamination of wounds where anaerobic conditions developed.

Method of diagnosis
Diagnosis is made by culture of C. botulinum or demonstration of specific toxin in serum, gastric aspirate, faeces, implicated food or wounds. Electromyography may be useful in corroborating the clinical diagnosis.

Incubation period

Classical botulism occurs within 12–36 hours (sometimes several days) after eating contaminated food. The incubation period for infant botulism is unknown due to difficulty in determining the precise time of ingestion. Shorter incubation periods are associated with more severe disease and higher case-fatality rates.

Public health significance & occurrence

Botulism is a rare disease internationally. However missed diagnoses particularly for intestinal botulism are likely due to low clinician suspicion and limited laboratory diagnostic capacity in many areas.

There have been only six cases of botulism reported in Australia between 1991 and 2003. Two of these occurred in Victoria in 2000 and 2001 (Communicable Diseases Network Australia - National Notifiable Diseases Surveillance System).

C. botulinum has been identified as a potential bioterrorist agent.

Reservoir

It is most commonly found in soil and agricultural products. Spores have been found in marine sediments and the intestinal tracts of animals, including fish.

Mode of transmission

Classical botulism is acquired by ingestion of inadequately cooked food or processed or refrigerated foods in which toxin has formed, particularly canned and alkaline foods. Most cases of wound botulism are due to ground-in soil or gravel. Several cases have been reported amongst chronic drug users.

Infant botulism arises from ingestion of spores rather than pre-formed toxin. Sources of spores include foods such as honey and dust. Honey has been described in the US literature as a source of infection but never implicated in Australia and surveys of Australian honey have failed to identify C. botulinum.

Period of communicability

Secondary transmission has not been documented.

Susceptibility & resistance

Everyone is susceptible to infection.

Control measures

Preventive measures
Ensure effective control of processing and preparation of commercially canned and preserved foods.

Educate people undertaking home canning and other food preservation techniques about cooking time, pressure, temperature, adequate refrigeration and storage. The absence of a bulging lid on tinned food does not preclude C. botulinum contamination.

Control of case
Botulism is a medical emergency. Suspected cases should immediately be referred for specialist care and trivalent botulinum antitoxin (types A, B, E) administered as soon as possible. Antitoxin is not used in infant botulism due to the risk of anaphylaxis. Antibiotics do not affect the course of the disease.

For wound botulism, in addition to antitoxin the wound should be debrided or drained, and appropriate antibiotic prophylaxis against other potential infections should be administered.

Isolation or quarantine is not needed but hand washing is indicated after handling soiled nappies. Usual sanitary disposal of faeces from infant cases is acceptable.

Any implicated food should be retained for collection and investigation by public health authorities. Contaminated utensils should be cleaned by boiling or with household bleach.

Control of contacts
Those who have eaten incriminated food should be purged with emetics, gastric lavage or high enemas. Administration of polyvalent antitoxin to asymptomatic individuals should be considered carefully, assessing potential protection against the risk of sensitisation and severe reactions to horse serum.

Control of environment
Environmental health officers and food safety officers should coordinate the appropriate disposal of implicated food.

Outbreak measures

An outbreak of botulism is defined as one or more cases of disease. The immediate aim is to identify possible sources of the disease and other people possibly exposed. Recall any implicated food immediately and send samples to the Microbiological Diagnostic Unit for analysis. Take sera and faeces from cases as well as exposed but asymptomatic persons for analysis, before administration of antitoxin.

Undertake efforts to recover and test implicated foods. This should be coordinated through Food Standards Australia New Zealand (02) 6271 2222.