Caused by the gram-positive, anaerobic bacteria Clostridium botulinum, botulism is a rare but severe form of poisoning. C. botulinum is found in soil and untreated water worldwide. The bacteria can also be found in undercooked and improperly preserved or canned foods—especially those with a low acid content. C. botulinum sometimes occurs normally in the stool of infants. It is one of the most potent bacteria known: If evenly distributed, as little as 1 g can kill more than 1 million people.

There are three main types of botulism, each characterized by the way the disease is transmitted: foodborne botulism, wound botulism, and infant botulism. The number of reported cases worldwide has been decreasing, mostly because of improved canning and food preservation methods. According to the National Institutes of Health, approximately 145 cases of botulism are seen in the United States every year. Of these, almost 65% are infant botulism. However, the incidence of wound botulism, which was once exceedingly rare, is now on the rise, presumably due to increased injectable drug use.

Initially used to treat conditions such as cervical dystonia and blepharospasm, two botulinum toxin preparations are licensed in the United States by the Food and Drug Administration. However, on- and off-label use of these preparations has grown. Botulinum toxin A is now available by prescription for therapeutic and cosmetic use. The formulation is normally highly diluted. In 2004, the Centers for Disease Control and Prevention (CDC) confirmed four cases of botulism in adults following cosmetic injection of an unlicensed and highly concentrated botulinum toxin A preparation. All four individuals became severely ill, but they all survived.