Tuberculosis is caused by germs that are spread from person to person through the air. TB affects the lungs and the throat and kills nearly 2 million people each year around the world.

The general symptoms of TB include feelings of sickness or weakness, weight loss, fever, and night sweats. When the disease attacks the lungs, symptoms include coughing, chest pain, and coughing up blood.

Thanks to antibiotics and other measures, the TB rate in the United States has been falling for years. Last year, it hit an all-time low - a total of 13,767 cases or about 4.6 cases per 100,000 Americans.

TB is spread the way other airborne illnesses are spread: through coughing and sneezing. The germs can float in the air for several hours, depending on the environment. People who breathe in the air containing these TB germs can become infected.

The disease is not spread through kissing, touching, shaking hands, sharing food or drink, sharing toothbrushes, or touching bed linens or toilet seats, according to the Centers for Disease Control and Prevention.

Regular or drug-susceptible TB is easily treated with antibiotics when caught early. But health officials worry about "multidrug-resistant" TB, because it can withstand the two mainline antibiotics most often used to treat TB — isoniazid and rifampin. About 1.2 percent of U.S. TB cases fall into that category, according to CDC statistics.

There have been 49 cases of drug-resistant TB documented since 1993. Of the 49 cases, 32 occurred between 1993 and 1999 and 17 were reported from 2000 to 2006. The largest number of cases (19) were reported in New York, while 11 were reported in California.

Twenty-three of the drug-resistant cases were among U.S.-born patients and 25 were foreign-born persons. One case was diagnosed in a person of unknown origin.

Even more rare is "extensively drug-resistant" TB - or XDR-TB. This is when TB does not respond to at least three of six classes of second-line drugs. Last year, there were two U.S. cases of that infection.

According to the CDC, resistance to anti-TB drugs can occur when antibiotics are misused or mismanaged. Examples include when patients do not complete their full course of treatment; when health-care providers prescribe the wrong treatment, the wrong dose, or length of time for taking the drugs; when the supply of drugs is not available; or when the drugs are of poor quality.

People most at risk for drug-resistant TB are people who do not take their TB medicine regularly; people who develop active TB again after having taken TB medicine in the past; people who come from areas of the world where the disease is common; and people who have spent time with someone known to have drug-resistant TB.

To guarantee recovery from TB, people infected with the disease should take all of their prescribed medication, the CDC says.