Role of poverty will get an airing
Does environmental stress lead to reactivation?
TB experts will gather in Vancouver in February to focus on the relationship between poverty and tuberculosis, with "TB Among the Disadvantaged," the theme for the third annual meeting of the North American Region of the International Union Against Tuberculosis and Lung Disease (IUATLD).
One hundred years ago, discussions about TB almost always included references to poverty, says Carole Mitnick, managing director for the Institute for Health and Social Justice in Boston, and a scheduled speaker for the conference. Today, despite a widespread recognition that poverty and TB are linked, the topic usually takes a backseat to an emphasis on treatment, she says. Part of the reason is politics, Mitnick adds. "The current political climate makes it not particularly fashionable to focus on the roots of TB," she says. "Doing so would require that more efforts be made outside the health care sector like changing social policy to address issues related to housing, welfare, or education."
The current focus can do little to address gaps between rich and poor that contribute to TB incidence, Mitnick says. "In developing countries, you hear poor nations can’t do much about TB because the treatment is too expensive," she says. "And here in the United States, unless TB affects wealthy people, it’s not a hot issue either."
Unless leaders move to address an inequitable distribution of resources, even the most inexpensive treatment-based approaches will continue to fail, she adds.
Poverty as a stress on the immune system?
One reason may be that burdens imposed by poverty may cause stress on the immune system, which in turn may increase the likelihood that people infected with TB will develop active disease, she says. But she admits it’s difficult to quantify the effects of such stress particularly since the United States collects no data on the economic status of TB cases.
Some researchers, chiefly P.D.O. Davis in England, have hypothesized that stresses suffered by recent immigrants may account for the comparatively high rates of reactivation of latent disease found among this group, says Patrick Zuber, MD, MPH, medical epidemiologist at the Division of Tuberculosis Elimination at the Centers for Disease Control and Prevention. But other factors remain that can be more clearly related to the increase, he adds.
"One factor, which I’m sure plays some part, is the fact that TB is detected once immigrants arrive because there is more active screening," he says.
A second factor is a bit more complicated. Since the risk for reactivation is greatest within the first two years following exposure, and since immigrants to the United States are usually no longer exposed to TB as often as they were in their homeland, recent immigrants include a higher proportion of people recently infected than those who have been living here for 10 years, Zuber says.
It may also be that the stress associated with migration predisposes people with latent TB toward reactivation, he adds. "But that has been very difficult to quantify."
As a graduate student preparing her master’s thesis, Mitnick studied the impact of poverty on TB incidence. She took 13 years of data from census and case reports and used them to analyze TB incidence among various groups of foreign-born immigrants to Massachusetts. Particular characteristics were examined to see if they correlated positively with a higher incidence of TB: For example, the availability of housing, the proportion of people living below the poverty line, the proportion getting public assistance, and the number of people living in a household.
To try to measure the effects of empowerment, Mitnick also looked at what happened to TB incidence among immigrants who were granted U.S. citizenship.
"The results were what you’d expect," she says. The negative factors were associated with a higher incidence of TB; and U.S. citizenship was associated with a lower incidence.
"I’d never take a dime away from treating people with active TB," she adds. But for those who are latently infected and living in poverty, Mitnick believes that research may one day show that attempts to treat active disease and to provide chemoprophylaxis to the infected, in themselves will not suffice to defeat the disease.
[For more information on the IUATLD conference, contact Dr. Menn Biagtan at the British Columbia Lung Association. Telephone: (604) 631-5864. Fax: (604) 731-5810.]
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