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For years, Phoenix firefighters have been contracting tuberculosis at an unusually rapid rate. Since 1992, about 250 city firefighters--roughly 20 percent of the force--have tested positive for TB.
Or have they?
Now, fire officials are wondering if those swelling skin tests might really be an indicator of something else: bird poop.
It seems bird droppings can contain a mycobacterium that causes the standard TB skin test to puff up in a manner similar to what's seen in people who really have the tuberculosis mycobacterium.
Dr. Richard Gerkin, who oversees the fire department's health center, recently briefed Phoenix fire chiefs on the latest with the perplexing TB problem. He posed the bird-poop theory as something that should be explored more thoroughly. Gerkin says he plans to call an Atlanta doctor who has documented the similarities between skin-test reactions from TB and from bird poop (officially called mycobacterium avium) to see if he'd like to do a study of Phoenix firefighters.
In the meantime, Gerkin says he's stopped recommending that some firefighters who test positive for TB take isoniazid, or INH, the common drug that prevents a TB infection from turning into the active TB disease. Gerkin says INH can cause liver cancer, and he doesn't want to risk that, especially for firefighters whose skin tests are borderline positive.
Big mistake, says Dr. Lee Reichman, executive director of the New Jersey Medical School National Tuberculosis Center and a past president of the American Lung Association.
Reichman says he's never seen a case of liver cancer from INH in the 25 years he's been at the national TB center. People who take INH can develop hepatitis, which can lead to liver cancer. But Reichman says that's rare.
What Reichman has seen, he says, is that INH has worked to control TB and its spread.
"Maybe this doctor [Gerkin] is right," Reichman says, "but I think you've got to have more direct evidence to refute what is effective and what works and what is national policy."
It used to be that the Phoenix department only tested firefighters who had been exposed to someone who had TB.
But in 1992, the department began routine testing of firefighters whom doctors considered to be at high-risk stations--downtown in particular. A dozen firefighters at Station 9, near Third Street and Indian School, turned up positive. A more systematic testing program ensued, under supervision from specialists at Good Samaritan Medical Center, Johns Hopkins University and, later, the National Institute for Occupational Safety and Health.
The more they tested, the more firefighters they found whose skin tests puffed up well into the positive range. The Phoenix Fire Department's TB rate currently stands at about 20 percent; that's compared to 12 percent in the San Francisco fire department and 8 percent in New York. Even locally, Gerkin says, Glendale and Peoria fire departments report only a 2 percent to 3 percent TB rate among firefighters.
Arizona has a high rate of TB anyway; health officials have theorized that's partly because of the proximity to Mexico, which has a high rate, but also because drug-resistant forms of the disease and its prevalence in AIDS patients are contributing to its spread. Fire officials assumed the firefighters, who also are paramedics, were coming into frequent and close contact with people who carry the disease. TB bacteria is spread through the air from person to person, usually through coughing or sneezing. Firefighters were thought to be contracting the disease when they rode with a TB-infected person in the back of an ambulance, for instance, or when giving them emergency medical care.
One study also showed that firefighter TB rates were highest at stations that serve neighborhoods along the I-10 and I-17 freeways.
So the department changed its procedures and got better equipment, including new face masks and upgraded ventilation systems in ambulances. And the rate of positive tests slowed, but it didn't stop.
Still, not a single Phoenix firefighter has ever developed an active case of TB, Gerkin says. He thinks that's odd, given statistics which he says show that at least 5 percent of those who test positive for TB develop active cases within a few years.
Reichman says that just proves the INH is working. He says he would not expect anyone taking the drug to develop active TB, at least not for many, many years.
Gerkin says he also started thinking more about an atypical mycobacterium after national health officials put out warnings that temperature-cooling misting systems like those used by restaurants could spread mycobacterium avium, which might be in the water. (Gerkin couldn't find a copy of the health bulletin, and officials with the National Centers for Disease Control say they've never heard of misters being a problem. They also say no one is sure where mycobacterium avium resides or how it's spread, and there is no evidence that it's prevalent in water.)
In the 1950s, Gerkin says, the Navy studied new recruits from across the country and found that many were testing positive for mycobacterium avium. The old study showed a high rate of positive test results from recruits coming from southern Arizona, which suggested that the mycobacterium was present here, possibly in the water.