6. INCUBATION PERIOD
From I to 7 days, although incubation periods up to 60 days are possible. (In the Sverdlovsk outbreak, incubation periods extended up to 43 days.)
Data from the Sverdlovsk outbreak indicate a modal incubation time of approximately 10 days for inhalational anthrax. However, the onset of symptoms occurred up to six weeks after the reported date of exposure. Such long incubation times presumably reflect the ability of viable anthrax spores to remain in the lungs for many days. Longer incubation periods may be associated with smaller inocula.
Source: Dixon TC, Meselson M, Guillemin J, and Hanna PC. Anthrax. New England J Medicine 341, 815-826, 1999.