Incidence of Anthrax Infection in Humans

Although an ancient disease, anthrax infection in humans is uncommon. The infection is seen mainly in animals - humans acquire infection through contact with them.

As a medical microbiology technologist working in a human healthcare facility in Nova Scotia, I have never actually worked with Bacillus anthracis - fortunate for me since I tend to be a touch clumsy and likely would have ended up with an infection somehow!

Anthrax is an ancient disease, but recently claimed our attention following the intentional release of spores through the U.S. mail system. Anthrax infections in humans are extremely rare in North America, and those that have occurred have been cutaneous (skin) infections acquired through handling infected carcasses, hides, wool, hair, meat and bone meal from infected animals. Even cutaneous infection is extremely uncommon! How rare is anthrax infection? The Centers for Disease Control and Prevention (CDC) estimates the risk of acquiring anthrax in the United States at approximately one case in 300 million people...sounds about equal to my chances of winning the lottery! Even following the intentional release of anthrax in the U.S. mail, the risk was only about 23 cases in 300 million people.

In Canada the last human case (until this year in Melfort, Saskatchewan) occurred in 1990. Prior to that, the last case reported was in 1961. Between the years 1931 and 1976, only 23 cases were reported with 6 of those occurring in 1936. The 1990 case involved a neck lesion on a woman in Vancouver who had purchased a wool sweater from a thrift shop. The sweater was thought to be the source of infection, but this was not proven.

There are 3 main types of anthrax - cutaneous, gastrointestinal and respiratory. Cutaneous anthrax is the most common type of infection that occurs in humans, followed by gastrointestinal, and finally respiratory. The severity of infection is respiratory, followed by gastrointestinal, then cutaneous.