The 60-day dose of antibiotics recommended by doctors
to prevent anthrax may not be long enough in some cases,
according to an analysis conducted by researchers at the
Johns Hopkins Bloomberg
School of Public Health.
Mathematical analysis shows that prophylaxis
antibiotics may be needed for as long as four months for
people exposed to high levels of anthrax spores. The new
model also provides a valuable tool for estimating exposure
doses in future outbreaks that can then be used to
determine the optimum window for antibiotic therapy. The
analysis appears in the July 28 issue of the Proceedings
of the National Academy of Sciences.
"Anthrax spores are expelled from the lungs at a
specific rate. Our model calculates the time it takes the
body to expel these spores. A single spore left behind can
germinate to cause disease," explained Ron Brookmeyer, lead
author of the study and professor of
biostatistics at the School of Public Health. "The
model we developed shows that larger exposures to anthrax
spores take longer to expel and require longer antibiotic
therapy. Sixty days of antibiotics provides adequate
protection in outbreaks with low exposure to spores.
However, four months of antibiotics are required for
outbreaks in which persons are exposed to large numbers of
Brookmeyer and his colleagues tested their model using
data from the 2001 anthrax attack on the United States and
the 1979 anthrax outbreak near a biological weapons plant
in Sverdlovsk, Russia. In both cases, the model's
predictions were consistent with the actual illness
"During the 2001 U.S. anthrax attacks, many people
failed to take the recommended 60-day course of
antibiotics. Full compliance was about 60 percent, or less
in some cases. Our model showed that the reason they didn't
get sick even without the antibiotics was because the
anthrax spore exposure levels were very low. If the
exposure levels were higher, there would have been more
casualties," Brookmeyer said.
The study was funded by the National Institute of
Allergy and Infectious Diseases.