TB Bug Slow to Replicate This week's bizarre news of a transatlantic traveler with tuberculosis raised questions about the microbe that causes the disease. In our regular segment "Science Out of the Box," Dr. Richard Chaisson of Johns Hopkins University explains that the TB bacterium is very slow to replicate, and this slows diagnosis, treatment and research.
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TB Bug Slow to Replicate

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TB Bug Slow to Replicate

TB Bug Slow to Replicate

TB Bug Slow to Replicate

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  • <iframe src="https://www.npr.org/player/embed/10672124/10672125" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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This week's bizarre news of a transatlantic traveler with tuberculosis raised questions about the microbe that causes the disease. In our regular segment "Science Out of the Box," Dr. Richard Chaisson of Johns Hopkins University explains that the TB bacterium is very slow to replicate, and this slows diagnosis, treatment and research.

Why TB Remains a Modern and Deadly Problem

Sick with tuberculosis, inmates at a Siberian prison wash down their medicine with milk while a masked nurse monitors them. Karen Kasmauski/Corbis hide caption

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Karen Kasmauski/Corbis

The United States has seen a decline in the number of tuberculosis cases from 27,700 in 1980 to 14,100 in 2005. Lindsay Mangum/NPR hide caption

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Lindsay Mangum/NPR

A 1939 poster asks for contributions to help prevent tuberculosis. Swim Ink 2, LLC/Corbis hide caption

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Swim Ink 2, LLC/Corbis

Until German physician Robert Koch first identified the bacteria behind tuberculosis in 1882, the often fatal, wasting disease of the chest was known simply as consumption or the white plague. Even after Koch found the disease's cause, doctors could do little for patients beyond keeping them well-nourished and in a clean environment. A cure remained another half-century away, with the discovery of an effective antibiotic in the mid-1940s.

Today, treatments for tuberculosis are threatened by the emergence of strains of the disease resistant to multiple lines of drugs. In a first since 1963, federal public health officials this month ordered a quarantine for Andrew Speaker, a 31-year-old Atlanta lawyer, who has been diagnosed with an extremely drug-resistant form of the disease. The patient currently is at the National Jewish Medical Research Center in Denver for treatment.

Such hard-to-cure strains are rare in the United States, but are gaining a foothold in countries like Russia and South Africa.

Here, a look at the state of TB in the United States and around the world:

Isn't tuberculosis a disease of the past?

TB is indeed ancient – it has been around at least since the pharaohs. Some scientists suggest it has been living with the human species for 3 million years. But it's also very much a disease of the present. It remains widespread around the world, with one in three people infected, according to the World Health Organization. But 90 percent of people infected with the germ never develop the disease. The bacteria are usually held in check by the immune system. The infection is more likely to develop into a disease when a person's immune system is compromised, for instance, due to HIV, other illnesses or aging.

How is TB spread?

People with TB disease can spread the bacteria through coughing, sneezing or simply talking. But infection usually happens only after prolonged exposure, according to Dr. Martin Cetron, director of the global migration and quarantine division at the Centers of Disease Control and Prevention.

"By and large, TB is spread through prolonged contact. This is not the type of pathogen that is transmitted by short, casual contact," Cetron said.

Only 10 percent of those infected with the germ go on to develop the disease.

Drug-resistant TB is not more infectious than other forms of TB. But repeated exposure to large concentrations of infected people – such as happens in prisons, overcrowded houses and hospitals – can increase a person's chance of infection. An immune system weakened by disease or even certain types of medication can also increase a person's risk of developing full-blown TB.

A person also becomes less infectious after the first week of treatment.

How widespread is TB in the United States?

TB has been on the decline here for decades, with the number of cases in 2006 – 13,767 – at an all-time low since national reporting began in 1953. But the rate of decline has slowed, a point of concern to public health officials, given the rise of TB strains resistant to multiple drugs.

Immigrants and minority groups continue to have higher rates of infection than whites in the United States. And the number of regular TB as well as multidrug-resistant cases is increasing in foreign-born people living in the United States.

How widespread is TB globally?

In 2005, WHO estimated 8.8 million cases worldwide, with 1.6 million deaths. About 200,000 of those deaths were patients with HIV. The majority of cases – 7.4 million – are in Asia and sub-Saharan Africa. In the Americas, there were approximately 352,000 cases in 2005, with 49,000 deaths.

If treatments exist, why is TB still such a problem?

Access to treatment and diagnosis in poorer countries is an ongoing obstacle. The HIV pandemic also complicates attempts to eradicate TB: The AIDS virus, which attacks the immune system, increases the likelihood that a TB infection will become a full-blown disease. HIV is considered the single most important factor in the increase of TB in Africa since 1990. Emerging drug-resistant strains of TB are also hampering efforts to stamp out both diseases.

What is drug-resistant TB?

MDR-TB, or multidrug-resistant TB, is a form of the TB bacteria that is resistant to two of the most powerful TB drugs – isoniazid and rifampsicin. When these so-called first line drugs don't work, doctors resort to a second line of drugs. But these aren't as fast-acting, cause more side effects and are more expensive. One U.S. case of drug-resistant TB last year cost nearly $500,000 to treat.

When the bacteria become resistant to the second line of drugs, too, the disease is considered to be XDR-TB, or extensively drug-resistant TB. At that point, treatment options are seriously limited. (Extensively drug-resistant TB is the form Andrew Speaker has. Speaker is currently in isolation in Denver.)

Between 1993 and 2006, there were 200,000 confirmed cases of TB reported in the United States. Of these, nearly 3,000 cases were classified as multidrug-resistant (MDR).

Of those 3,000 cases, 49 were extensively drug-resistant (XDR) TB, with 32 cases reported between 1993 and 1999, and 17 cases between 2000 and 2006.

The CDC doesn't have a confirmed outcome on eight of the 49 patients who had XDR TB. Among the other 41 patients, 12 people died. At least 10 of those who died were HIV positive.

Can extensively drug-resistant TB (XDR-TB) be cured?

About 30 percent of cases can be cured, according to the CDC. The severity of the disease, underlying medical conditions and a physician's access to treatment options all factor into a patient's ability to be cured.

Is XDR-TB rare?

TB that is resistant to nearly forms of drugs (XDR-TB) is rare. But in 2004, there were an estimated half a million cases globally of TB resistant to some drugs. Multidrug-resistant TB remains rare in the United States; the CDC recorded 124 cases out of more than 13,000 TB infections in 2005.

How does TB become drug resistant?

Resistance to antibiotics happens in two ways – a person either is infected with a resistant strain, or during treatment, the bacteria mutate or pickup resistance genes from other organisms. For most strains of the disease, the CDC recommends a course of drugs over a six- to nine-month period. (For multidrug-resistant strains, treatment can take up to two years.) If the drugs aren't taken precisely as prescribed, that could give the bacteria a window of opportunity to become resistant. This can be a serious problem in developing countries, where those infected may not have access to medical care.

What are the symptoms?

A skin test can detect whether a person has TB even before the full-blown disease appears. Symptoms are the same for normal TB as XDR-TB. Among the signs: a cough with thick, cloudy mucus, sometimes with blood, for more than two weeks; fever, chills and night sweats; fatigue, muscle weakness and weight loss.

In Depth