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27 February 2018

Causative agent

Human botulism is a rare but serious disease caused by neurotoxin produced by the bacteria, Clostridium botulinum, which can be found in soil, the environment and contaminated food.

Clostridium botulinum produces spores that are heat-resistant and exist widely in the environment, and in the absence of oxygen they germinate, grow and then excrete toxins. There are seven distinct forms of botulinum toxin, types A – G. Four of these (types A, B, E and rarely F) cause human botulism. Types C, D and E cause illness in other mammals, birds and fish.

Clinical features

Early symptoms are marked fatigue, weakness and vertigo, usually followed by blurred vision, dry mouth and difficulty in swallowing and speaking. Vomiting, diarrhoea, constipation and abdominal swelling may also occur. The disease can progress to weakness in the neck and arms, after which the respiratory muscles and muscles of the lower body are affected. The paralysis may make breathing difficult.

The symptoms are not caused by the bacterium itself, but by the toxin produced by the bacterium.

There are 5 categories of botulism depending on source of infection.

Foodborne botulism occurs when Clostridium botulinum grows and produces toxins in food prior to consumption.

Infant botulism occurs mostly in infants under 6 months of age. It occurs when infants ingest Clostridium botulinum spores, which germinate into bacteria that colonize in the gut and release toxins. In most adults and children older than about six months, this would not happen because natural defences that develop over time prevent germination and growth of the bacterium. Clostridium botulinum in infants include constipation, loss of appetite, weakness, an altered cry and a striking loss of head control. Although there are several possible sources of infection for infant botulism, spore-contaminated honey has been associated with a number of cases.

Wound botulism is rare and occurs when the spores get into an open wound and are able to reproduce in an anaerobic environment. The symptoms are similar to the foodborne botulism, but may take up to 2 weeks to appear. This form of the disease has been associated with substance abuse, particularly when injecting black tar heroin.

Inhalation botulism is rare and does not occur naturally, i.e. it is associated with accidental or intentional (e.g. bioterrorism) events which result in release of the toxins in aerosols. Inhalation botulism exhibits a similar clinical picture to foodborne botulism.

Other types of intoxication

Botulism of undetermined origin usually involves adult cases where no food or wound source can be identified. These cases are comparable to infant botulism and may occur when the normal gut flora has been altered as a result of surgical procedures or antibiotic therapy.

Adverse effects of injecting pure botulinum toxin have been reported as a result of its medical and/or cosmetic use in patients. Injectable products containing botulinum toxin are pharmaceutical products and prescription medicines. Procedures involving injection of botulinum toxin should only be prescribed and performed by a locally registered medical practitioner. Although purified and heavily diluted botulinum neurotoxin type A is used, occasional side effects are still observed. 

Incubation period

For foodborne botulism, symptoms usually appear within 12 to 36 hours, ranging from 4 hours to 8 days after exposure. For wound botulism, the incubation period may last up to 2 weeks. Following inhalation, symptoms become apparent between 1 – 3 days, with longer onset times following lower level of intoxication.


Antitoxin should be administered as soon as possible once diagnosis is made. Early administration is effective in reducing mortality rate. Severe botulism cases require supportive treatment.


Foodborne botulism

  • For those individuals who do home-canning, follow proper canning requirements and hygienic procedures and boil home-canned food for at least 10 minutes before eating because botulism toxin can be destroyed by high temperatures.
  • Avoid consumption of food from containers (e.g. canned food) that appear to be damaged, bulged or spoilt.
  • Follow the handling and storage instructions given by manufacturers of canned, bottled and vacuum packed foods.

The “5 Keys to Food Safety” are 5 simple and effective keys for people to follow when handling food to prevent foodborne botulism:

  1. Choose (Choose safe raw materials);
  2. Clean (Keep hands and utensils clean);
  3. Separate (Separate raw and cooked food);
  4. Cook (Cook thoroughly); and
  5. Safe Temperature (Keep food at safe temperature).

Please refer to the Centre for Food Safety website via the link below for more practical tips:

Infant botulism

As honey might contain the bacteria that cause infant botulism, infants before the age of 1 year should not be fed honey.

Wound botulism

  • Should promptly seek medical care for infected wounds.
  • Should not inject street drugs.

For details about botulinum toxin injection, please refer to: