Botulism

Causative agent

Botulism is a rare but serious illness caused by a neurotoxin produced by Clostridium botulinum bacteria. The bacteria produces spores that are heat-resistant and exist widely in the environment. In the absence of oxygen, the spores germinate, grow and excrete botulinum toxins. The toxins can block nerve functions and lead to paralysis. 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.

Main categories of botulism include:

• Foodborne botulism occurs when food is contaminated with botulinum toxin prior to consumption. Common sources of foodborne botulism include food that have been improperly canned, preserved, or fermented.
• Infant botulism occurs when infants ingest Clostridium botulinum spores in contaminated soil or food, which germinate and release toxins in the intestines. This would not happen in most adults and children older than 6 months because natural defences in intestines that develop over time prevent germination and growth of the bacterium. Although there are various possible sources of infection for infant botulism, spore-contaminated honey has been associated with a number of infant botulism cases.
• Wound botulism is rare and occurs when the spores get into an open wound and produce toxins. This form of the disease has been associated with substance abuse that involves injection, and traumatic injury.
• Iatrogenic botulism occurs if too much botulinum toxin is injected for medical or cosmetic reasons.
• Other types include inhalation botulism (e.g. bioterrorism), waterborne botulism and botulism of undetermined origin. These cases of botulism are very rare.

Clinical features

Early symptoms are marked fatigue, muscle weakness, usually followed by blurred vision, difficulty in swallowing and slurred speech. Vomiting, nausea and diarrhoea may also occur in foodborne botulism. The disease can progress to weakness in the neck and arms, the respiratory muscles and muscles of the lower body may be affected making breathing difficult. For infant botulism, symptoms include constipation, loss of appetite, weakness, an altered cry and a striking loss of head control. Due to the weakening of associated muscles and the fact that botulinum toxin may spread and affect other areas beyond the injection site, patients with iatrogenic botulism may experience drooping of the eyelids, double vision or blurred vision, problems with chewing, hoarseness of voice or even difficulties in swallowing, speaking or breathing.

Incubation period

For foodborne botulism, symptoms usually appear within 12 to 36 hours after exposure, but may also take up to 8 days to appear. For wound botulism, the incubation period may last up to 2 weeks. Symptoms of iatrogenic botulism may appear from several hours to several weeks after injection.

Management

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

Prevention

Foodborne botulism

• For people who do home-canning, follow proper canning requirements and hygienic procedures. As botulism toxin can be destroyed by high temperatures, boil home-canned food for at least 10 minutes before eating to destroy any botulism toxin that may be present.
• 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 food.
• The “5 Keys to Food Safety” are 5 simple and effective keys for people to follow when handling food to prevent foodborne diseases:

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:

http://www.cfs.gov.hk/english/consumer_zone/consumer_zone_5_Keys_to_Food_Safety.html

Infant botulism

As honey can contain the bacteria that cause infant botulism, children younger than 12 months should not be fed with honey.

Wound botulism

• seek medical care promptly for infected wounds
• avoid injecting illicit drugs

Iatrogenic botulism

Injectable products containing botulinum toxin are pharmaceutical products and prescription medicines. Botulinum toxin injections should only be performed by a locally registered doctor. Customers should look for his or her full name against the list of registered medical practitioners of the Medical Council of Hong Kong (https://www.mchk.org.hk/english/list_register/doctor_list.php) as well as his or her professional qualifications and relevant experience.