They used to call it consumption. Counties used to run sanatoriums to house the patients, and it used to be that people were advised by their physicians that a drier climate might help their struggle against tuberculosis. We're still struggling.

Despite the progress we've made in treating many diseases, the TB organism is adept at clinging to existence much as the disease itself clings to patients.

"It's always an important health issue because when you have an active case there's a potential for a lot of exposure," said Margaret Gesner, health officer for the Caledonia-Mount Pleasant Health Department. Yet it's not so prevalent that public health officials advise people to wear masks.

Numbers

Although the rate of TB infection has been decreasing over the past few years, the rate is slowing even as the number of cases and the rate of infection have reached their lowest point since national reporting began in 1953. There had been a resurgence of tuberculosis from 1985 to 1992. From 1993 to 2000, the rate of new cases decreased at about 7 percent annually. From 2000 to 2008, however, it decreased at just over 3 percent annually.

In 2008, there were more cases in Hispanics than in any other racial or ethnic group in the nation, according to the U.S. Centers for Disease Control and Prevention. In Wisconsin, the largest proportion of 2008 cases (35 percent) was among Asians.

There are also disparities among various groups. The CDC reports that foreign-born people have a disproportionately large share of tuberculosis. Their rate was almost 10 times greater than that among people born in the United States in 2008. Among people born in the United States, the rate among blacks was seven times higher than in whites.

As it has for many other diseases which we thought were succumbing to modern medicine, the inescapable fact of evolution is also generating TB strains that are resistant to one, a few, or most antibiotics. Fortunately that isn't a problem here in Wisconsin or even in this hemisphere. The Americas - except for Peru and Guatemala - had the lowest proportions of drug-resistant TB, according to a World Health Organization report released earlier this year.

TB here

Resistant strains of TB do show up in Wisconsin but not in large numbers. In 2006, there were six cases of drug-resistant TB, according to the state. In 2006, there were three, in 2008 just one.

There aren't that many cases of TB in Wisconsin to begin with. From 2002 to 2008, the state averaged 76 per year with about half of those in Milwaukee County. In 2008, Racine County had four cases of TB, but it had none in 2005 and 2006 and two in 2007, according to state data.

"It does seem to be intermittent," said Teri Hicks, a nurse who is director of community health programs for the Racine Health Department. Fewer than five cases are being tracked by the department now, she said.

The presence of the disease does mean more demands on public health nurses. Because of concerns about the spread of TB, Hicks said, nurses visit patients and watch them take each scheduled dose of medication. How often that happens depends on the case and the medication, "but the nurses may go every day. They may go twice a week."

This can turn into a significant amount of nursing time, she said. "But in the long term it's much more responsible fiscally and public health-wise."

"Most people don't die from tuberculosis. It's unusual to die from TB because most of it is very treatable," said Cheryl Mazmanian, health officer for the Western Racine County Health Department.

Contracting it is a matter not only of contact with a person with full-blown TB but also of the duration of contact, Gesner said. As a public health investigator she once spent time in an airport where an infected worker had been preparing airline lunches. But the room had a high ceiling and a good ventilation system, she said, and no one became infected because of that worker. Continuing contact in a home may result in infection. "But if you're in a cubicle probably no one around you is going to get sick."

Like the other county health departments, Mazmanian's sees only a handful of cases each year, typically fewer than 10 for the area west of Interstate 94. And despite the prevalence of the disease in people born outside the United States, here it isn't the case.

"We really haven't seen it in only our immigrant population," Mazmnian said. "The cases that we're seeing we're seeing in people from areas where TB is prevalent."

It may also be that the cases we're seeing now are also from the time when TB was more prevalent in the United States, she said. People exposed when they were younger had latent infections, and as they age their immune systems weaken and the disease burgeons.

The pollution factor

TB has proven such a tough foe because it has any number of tricks to prevent the body from killing it.

Adrie J.C. Steyn, assistant professor of microbiology at the University of Alabama at Birmingham, has devoted his career to studying tuberculosis bacterium. In research published in the Journal of Biological Chemistry last year, Steyn and his colleagues wrote that carbon monoxide and nitric oxide can signal the TB bacterium to become dormant. This is why TB can last so long. It grows in oxygen-rich environments, but without oxygen it has been preserved in test tubes for 12 to 13 years.

Normally a bacterium which enters the lungs will be swallowed by macrophages, one type of immune cell, and attacked by others. TB can resist this by modifying the macrophage to prevent its own destruction. As a result, the TB containing macrophages and other immune cells form clumps in the lungs called granulomas.

"To some extent it helps to prevent spreading of the disease," Steyn said.

But it also means the bacteria can linger. As people age and their immune systems weaken, or if they contract HIV, the latent TB can turn into full-blown disease, Steyn said. This is where carbon monoxide may play another role.

Ordinarily, a macrophage which has swallowed TB but can't destroy it may destroy itself in order to also destroy the invader. Biologists call this self-destruct sequence apoptosis, but large amounts of carbon monoxide can shut it down.

The reason this is important is because of the environment we live in.

It's one thing to study TB in the lab and another to generalize that to humans. We don't yet know how the TB dormancy genes work in humans or what else happens inside the body, Steyn said, but the hypothesis is that if people inhale large amounts of carbon monoxide - from cigarettes or indoor air pollution - that may shut down apoptosis in those macrophages and induce reactivation of TB.

"Cigarette smoke contains vast amounts of carbon monoxide as well as nitric oxide, too," Steyn said. And smoking is strongly associated with the presence of tuberculosis, he said. Scientists know it affects the ability of macrophages to swallow invading organisms.

The same relationship can be seen elsewhere in the world. Asians have a high proportion of TB cases, and Steyn said that about 80 percent of the Chinese population smokes. In India smoking is widespread, and many rural people rely on wood or other vegetative matter for cooking fuel, and that generates large amounts of carbon monoxide. In the Western world, we have automobiles which produce large quantities of nitrous oxides; generally we worry about them because they form smog.

Many people seem to think that TB is part of the past, Hicks said. And our memory of it does come out of the era of hoop skirts, corsets and dressing for dinner at 8. During the 19th and early 20th centuries tuberculosis was the nation's leading cause of death with estimates of 450 deaths per day. But unlike hoop skirts, corsets, and dressing for dinner, tuberculosis hasn't faded with the yellowed pages of history.