As a few anthrax-tainted letters appeared in mail rooms across the Eastern seaboard last month, one of the more troubling developments for members of the public was how many things public health authorities seemed not to know about the disease. Were some people more susceptible than others? How many spores were necessary to come down with the often-lethal inhaled form of the disease? And how easy could it be for a sealed envelope to leak spores as it traveled through the postal system?
As recently as this week public health departments in affected areas like New Jersey were still insisting that the question of who contracted anthrax was simply a matter of how many spores a particular individual inhaled.
But it seems clear that people who are middle-aged and older are more susceptible to contracting anthrax than those in their 20s and 30s, and substantially more susceptible than teenagers and children. What's more, evidence supporting this conclusion was published almost a decade ago.
Consider the numbers. Have you noticed how the victims of inhalation anthrax tend to run toward the older side? The numbers are fairly striking and there's good reason to believe it's no coincidence.
To date, according to a Centers for Disease Control study released on Friday ("Bioterrorism-Related Inhalational Anthrax: The First 10 Cases Reported in the United States"), 10 Americans have contracted the inhalation variety. Twelve contracted the more treatable cutaneous (or skin) variety.
The average age of those who contracted inhalation anthrax was 56, and only two victims were under 50 (a 47-year-old man in Washington, D.C., and a 43-year-old woman in New Jersey). Of those who contracted skin anthrax all were under 50, with the exception of a woman in New Jersey who works near the contaminated Hamilton Township Post Office. In fact, besides the 51-year-old New Jersey woman, no one who has contracted skin anthrax (whose age has been made public) is over 40.
The overall numbers in question are quite small. And determining their precise relevance would require compiling the ages of persons in the contaminated workplaces, something the CDC says it is now in the process of doing. In a Friday teleconference, CDC anthrax specialist Dr. Bradley Perkins would say only that anecdotal evidence collected thus far showed the victims were "slightly older than what you'd expect based on what's been observed."
But the recent anthrax outbreak isn't the first evidence that there is a significant correlation between age and susceptibility to inhalation anthrax. In 1979, a Soviet biological weapons facility in the city of Sverdlovsk (now Ekaterinburg) accidentally released anthrax into the air, infecting 78 people, the largest outbreak of inhalation anthrax in the 20th century. For years, Soviet authorities insisted that the outbreak was naturally occurring. But after the fall of the Soviet Union the truth slowly began to come out. In 1994 a team of American researchers, led by Harvard biologist Dr. Matthew Meselson, published a study of the outbreak in Science Magazine. According to the Meselson study, the mean age of victims was 42 for men and 55 for women. Moreover, there were no victims under 24. Meselson calls these numbers "highly significant" and believes there is a heightened susceptibility to inhaled anthrax for those middle-aged and over.
Salon was unable to obtain comment from the CDC in time for publication about whether its officials had previously been made aware of the findings of the Sverdlovsk study.
Some experts note, sensibly enough, that many respiratory illnesses (like flu, for instance) strike the old harder than they do young adults with healthy immune systems. But another finding of the Sverdlovsk study points to the conclusion that heightened susceptibility to anthrax is distinct from that which we associate with other diseases. Many infectious diseases that strike the old disproportionately also hit the very young. But there were no children infected with inhalation anthrax in the Sverdlosk study.
Since the study of the outbreak occurred more than a decade after it happened, and since the precise range of people who were exposed is uncertain, it is difficult to draw precise conclusions from the lack of any children among the 78 infected cases. But through field study and interviews conducted by Dr. Jeanne Guillemin they were able to determine that many children must have been exposed to concentrations of anthrax spores similar to ones that infected older residents of the city.
"During our second trip [to the area] we went looking for schools," Meselson told Salon, "and there were a sizable number of schools right along the path of the [anthrax] plume." Those schools, Dr. Guillemin was able to determine, were in session on the day of the accidental release. "Certainly there were a lot of people under 24 who were mingled throughout those people [who contracted inhalation anthrax]," says Meselson. And they did not contract the disease. Meselson also notes another admittedly anecdotal study of inhalation anthrax outbreaks in early 20th century Russia which also shows a telltale lack of young victims of the disease.
It's important to note that no one believes children, adolescents or young adults are immune to inhalation anthrax. Meselson assumes that sufficiently high doses of anthrax spores inhaled would overwhelm whatever unique protections the very young might have against contracting the disease. But age does appear to be a significant determinant of anthrax susceptibility. And that seems to be something the public should know.
"The Sverdlosk data," says Guilleman, the Boston College professor and MIT security studies program senior fellow who conducted much of the field work in Meselson's study, "suggests that doctors should exercise caution in prescribing antibiotics to children on the suspicion of inhalation anthrax because the risks of the antibiotics may far outweigh the probability of children becoming infected with the disease."