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A Killer Returns: The Face of the Tuberculosis Epidemic

Tuberculosis continues to exact its terrible toll on humankind. Worldwide, a person is newly infected with TB every second, and overall nearly 2 billion people have been exposed to TB bacteria. During the 1990s, bright hopes that the disease would be vanquished by 2025 were extinguished as a variety of medical and social factors helped TB surge back to its familiar position among major causes of death.

TB strikes hardest in young adulthood
TB strikes hardest in young adulthood
Credit: WHO

Around 1985, cases of TB began to rise in the United States. Several interrelated forces drove the resurgence, including increases in prison populations, homelessness, injection drug use, crowded housing, and increases in populations in long-term care facilities. Along with increased immigration of people from countries where TB is endemic, these forces provided ideal conditions for TB transmission. Adding the most fuel to the fire, however, were the HIV/AIDS epidemic and increases in multidrug-resistant TB (MDR TB).

A Global Emergency

TB is a contagious disease. When people with active TB cough, spit, or even talk, bacteria that cause the disease are propelled into the air. A person needs to breathe in just a few TB bacteria to become infected. Without treatment, a person with an active case of TB will infect between 10 and 15 people a year. Infection with TB bacteria, however, does not necessarily lead to disease. In a person with a healthy immune system, TB germs take up residence in lung cells, but enter a kind of suspended animation and never cause widespr​ead disease. Only between 5 and 10 percent of all healthy people infected with the germ will develop active TB at some point. In people with decreased immune function, whether due to HIV/AIDS, poor nutrition, or old age, the odds are much worse. When infected with both HIV and TB, for example, a person has a one in ten chance of developing active TB each year (compared with a one in ten chance over a lifetime for people without HIV).

A worldwide epidemic
A worldwide epidemic
Credit: WHO

TB kills between 2 and 3 million people each year and is the leading cause of death among young adults and a major cause of death among women of childbearing age. So great was the concern about the worldwide epidemic of TB that in 1993, the World Health Organization (WHO) declared TB a global emergency, the first time a disease had ever achieved that dubious distinction.

Birth of a Superbug

Perhaps the most alarming aspect of the present epidemic is the rise in MDR TB. According to a survey conducted by WHO, up to 4 percent of all TB cases worldwide are resistant to more than one anti-tuberculosis drug. In parts of Eastern Europe, nearly half of all TB cases resist at least one first-line drug. Most of the burden of MDR TB falls on poor countries, but the United States has seen outbreaks of drug-resistant TB as well. In the early 1990s, New York City had an epidemic of MDR TB that cost almost $1 billion to control.

With proper treatment, almost all cases of TB are curable. But proper treatment is not always easy to attain. Typically, a TB patient takes four different antibiotics for at least two months, then two drugs for four more months. Hitting TB germs with several drugs simultaneously lessens the chance that naturally occurring mutations in the bacteria will allow some to escape destruction. However, because the drugs often cause unpleasant side effects and because patients start feeling better after a month or so, not everyone completes the full course of treatment. In many less developed countries, where TB is most common, drug supplies may be inadequate and medical services spotty.

Unfortunately, partial treatment for TB is worse than no treatment at all. TB bacteria that linger following incomplete therapy are likely to resist anti-tuberculosis drugs in future flare-ups. Worse still, people with active cases of MDR TB can pass those superbugs on to new victims.

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Last Updated August 12, 2010