Botulism is a rare but serious paralytic illness caused by a nerve toxin that is produced by the bacterium Clostridium botulinum. There are three main kinds of botulism: foodborne botulism is caused by eating foods that contain the botulism toxin; wound botulism is caused by toxin produced in a wound infected with Clostridium botulinum; and infant botulism is caused by consuming the spores of the botulinum bacteria, which then grow in the intestines and release toxin. All forms of botulism can be fatal and are considered medical emergencies. Foodborne botulism can represent a major public health threat, because there may be many other persons at risk of poisoning from eating the same contaminated food.
Types of Botulism
From 2001 – 2005, an average of 142 cases of botulism were reported each year. Of these, approximately 13% were foodborne, 66% were infant botulism, 19% were wound botulism, and 2% were unknown or other. Outbreaks of foodborne botulism involving two or more persons occur most years and are usually caused by eating contaminated home-canned foods. The number of cases of foodborne and infant botulism has changed little in recent years, but wound botulism has increased because of the injection of black-tar heroin. In recent years, California has experienced an epidemic of this form of botulism and we now report nearly three-quarters of the wound botulism cases in the country.
The initial symptoms are frequently double or blurred vision, drooping eyelids, and dry, sore throat. Progressive descending paralysis, usually symmetrical, may then follow. After affecting cranial nerve function (to cause slurred speech, difficulty swallowing, and inability of the neck muscles to support the head), paralysis of the extremities and respiratory muscles can occur. Infants with botulism appear lethargic, feed poorly, are constipated, have a weak cry, and poor muscle tone. These are all symptoms of the muscle paralysis caused by the bacterial toxin. In foodborne botulism, symptoms generally begin 18 to 36 hours after eating a contaminated food, but they can occur as early as 6 hours or as late as 10 days after.
Physicians should consider the diagnosis if the patient's history and physical examination suggest botulism. However, these clues are usually not enough to allow a definitive diagnosis of botulism. Other diseases, such as Guillain-Barré Syndrome, stroke, and myasthenia gravis, can appear similar to botulism, and special tests may be needed to distinguish these conditions from botulism. These tests may include a brain scan, spinal fluid examination, nerve conduction test (electromyography [EMG] with repetitive nerve stimulation), and a Tensilon test for myasthenia gravis. The most direct way to confirm the diagnosis is to demonstrate botulinum toxin in the patient's serum, stool, or wound by injecting appropriate clinical specimens into mice and looking for signs of botulism in the mice. The bacteria can also be isolated from the stool of persons with foodborne and infant botulism, and can be recovered from the wounds of persons with wound botulism. In California, tests for botulism can be performed only at the California Department of Public Health Microbial Diseases Laboratory in Richmond, CA, and at the Los Angeles County Department of Health Services laboratory in Los Angeles.
Botulism can be prevented. Foodborne botulism has often been from homecanned/home-preserved foods with low acid content, such as asparagus, green beans, beets and corn. However, outbreaks of botulism have also occurred from more unusual sources such as chopped garlic or onions in oil, improperly handled baked potatoes, and home-fermented fish. Persons who do home canning should follow strict procedures to reduce contamination of foods. Oils infused with garlic or herbs should be refrigerated. Potatoes which have been baked while wrapped in aluminum foil should be kept hot until served or refrigerated. Because the botulism toxin is destroyed by high temperatures, persons who eat home-canned foods should consider boiling the food for ten minutes before eating it to ensure safety. Instructions on safe home canning can be obtained from the UC Cooperative Extension, or from the US Department of Agriculture. Because honey can contain spores of Clostridium botulinum and this has been a source of infection for infants, children less than 12 months old should not be fed honey. Honey is safe for persons 1 year of age and older. Wound botulism can be prevented by promptly seeking medical care for infected wounds and by not injecting street drugs.