Anthrax tests fall into two categories: those for exposure and the presence of anthrax in the environment and those for infection. A nasal swab test, which involves swabbing the inside of a nose and performing a culture on the sample collected, can reveal the presence of spores, and thus exposure, but a positive test does not indicate infection. Humans are relatively resistant to anthrax infections, and the number of spores required to cause inhalational anthrax varies. Even a person exposed to spores will not become ill unless the spores germinate, a process that can take up to 60 days. Therefore, nasal swabs are not recommended to document anthrax exposure or illness.
Anthrax infection is diagnosed by culturing the bacteria, using a specimen appropriate to the form of the disease suspected, such as from blood, skin lesions, or respiratory secretions, or by measuring antibodies in the blood. For inhalational anthrax, a chest X-ray can also be helpful as can a test of cerebrospinal fluid if signs of meningitis are present.
Culturing of a sample from either an environmental source or a bodily fluid such as blood can take several hours to several days. The specimen is incubated in artificial media, where the bacteria can grow. (Read more about blood culture.) Conventional biochemical tests are then performed to identify the bacteria and susceptibility testing is done to select the best antibiotic for therapy.
Testing may also be performed to rapidly detect anthrax DNA in the blood and to confirm culture findings. Because of the incident in 2001, there is great interest in being able to rapidly detect anthrax exposure and infection. Other tests are being developed with this in mind.