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TUESDAY, July 29, 2003 (HealthDayNews) -- Antibiotic treatment after exposure to anthrax might need to be given much longer than the 60-day course typically recommended, researchers say.
"Sixty days of antibiotic treatment may not be enough to confer protection," says Ronald Brookmeyer, a professor of biostatistics at Johns Hopkins Bloomberg School of Public Health and a member of the research team. "If the exposure to anthrax spores is high, we may need double that, to four months."
"This is not one size fits all," says Brookmeyer, adding that research is meant to add to the growing body of knowledge about how to handle a bioterrorist attack. The work appears in this week's issue of the Proceedings of the National Academy of Sciences.
Brookmeyer and his colleagues used a competing-risks model, often used by biostatisticians, to determine the best window for antibiotic therapy. A competing-risk model takes into account such factors as people who are exposed to one disease (anthrax), developing symptoms of other diseases, which may actually kill them first, or developing other symptoms that may mask the anthrax infection.
Brookmeyer's team found that 60 days of antibiotic therapy is probably adequate if the exposure to spores that cause the disease is low, but not if exposure is high.
Anthrax is caused by Bacillus anthracis, a bacterium that forms spores. These spores can live in the soil for many years and infect humans who handle products from infected farm animals or who inhale anthrax spores. More recently, of course, anthrax has been used as a biological weapon, such as when it was distributed via the U.S. Postal Service in 2001, causing 22 cases of infection.
If therapy is stopped too soon, the remaining spores can germinate and cause illness.
Early treatment with antibiotics can cure most cases of cutaneous anthrax, according to the U.S. Centers for Disease Control and Prevention. Another form, gastrointestinal, is more serious, as is inhalation anthrax. In 2001, half the inhalation anthrax cases were fatal.
Symptoms vary depending on form. With cutaneous exposure, a small sore that becomes a blister is often the first symptom. Nausea, loss of appetite and fever can occur first with gastrointestinal exposure. With inhalation anthrax, symptoms mimic a cold or flu. Symptoms can occur within seven days, but can also take up to 42 days for inhalation anthrax, the CDC says.
Brookmeyer notes his team's analysis takes into account the toxic dose levels. It is also based on a number of educated assumptions, such as the number of spores in a host that germinate.
The work is aimed at convincing people that they need to take the full course of antibiotic treatment prescribed.
"There were some people in the 2001 attack who did not take the full 60-day course," Brookmeyer says. The adherence rates in the 2001 outbreak, in fact, were only 64 percent, 61 percent and 31 percent, respectively, in the Washington, D.C., New Jersey and Florida clusters.
In the event of another attack, public health officials could look to the severity of the disease in those affected, in part to help assess what exposure level likely occurred, Brookmeyer says.
"It's a really neat paper," says Stephen Fienberg, a professor of statistics and social science at Carnegie Mellon University who served as the independent editor of the report. "It's the first time to my knowledge that this particular model has been brought to bear on this [anthrax problem]."
"It really tells us about a sensible time course for treatment for low and high exposure," he adds. "There are really planning implications."
More information
For general information on anthrax, try the U.S. Centers for Disease Control and Prevention
or the Department of Health and Human Services.
