Reports of a passenger infected with tuberculosis flouting international health regulations and flying into the United States put TB in the news earlier this year. More recently, medical researchers at Oxford University in England announced trials of a new TB vaccine — the first in almost 80 years — taking place in South Africa, where the disease is widespread and many strains are resistant to current antibiotic treatment.

Suddenly, tuberculosis, a highly contagious life-threatening illness that’s been on the decline in the United States since the 1950s, is a pressing concern. Globally, new infections and deaths from tuberculosis are increasing, most acutely in sub-Saharan Africa and Southeast Asia. Worldwide, tuberculosis kills 2 million people yearly. About one-third of the human population is infected with TB, with a new infection occurring every second.

I will never forget caring for my first patient with tuberculosis years ago. I tried to limit time spent near him, conversing with him from outside the doorway of his hospital room. The patient wore a mask when I entered his room, but removed it to take his medication. So, when I administered his medication, I would hold my breath afraid that I would contact the TB bacteria simply by breathing. We know much more now.

Mycobacterium tuberculosis, which causes TB, is spread in microscopic droplets that are released into the air when someone with the untreated, active form of TB coughs, sneezes or exhales. Although tuberculosis is contagious, it is not easy to catch. In general, infections occur only after long-term contact with an infected person. Thus, you are more likely to contract TB from a family member, coworker, roommate or friend than from a stranger on a bus or in a restaurant.

Although your body may conceal the TB bacteria, your immune system can protect you from becoming ill. This is why physicians make a distinction between active TB and latent TB. Active TB makes you sick and can be spread to others. The infection may be asymptomatic for years, even though it is active and causing damage to your lungs. Latent TB, sometimes called TB infection, causes no symptoms and is not contagious.

Your immune system begins to attack the tuberculosis bacteria two to eight weeks after you are infected. Sometimes, the TB bacteria die and the infection clears completely. In some cases, the bacteria remain in your body in an inactive state and cause no tuberculosis symptoms. In other cases, you may develop active TB.

Although it most commonly affects the lungs, tuberculosis can also invade other parts of the body including joints, bones, the urinary tract, the central nervous system, muscles, bone marrow and the lymphatic system. It can also spread throughout the body, attacking many organ systems at once.

People with weakened immune systems, particularly those suffering from HIV or AIDS, are extremely susceptible to tuberculosis. In fact, TB is the leading cause of death among people living with AIDS because it can increase the rate at which the AIDS virus multiplies.

Crowded living conditions with poor ventilation are, and always have been, a primary catalyst for the spread of tuberculosis. Thus the disease is frequently found in places of extreme poverty where residents lack access to medical care.

Frustratingly, sometimes the disease remains strong even when medical care is provided. Physicians and researchers continue to discover strains of TB that are resistant to available treatments. And even more dangerous are strains that are resistant to more than one anti-tuberculosis drug, leading to a condition called multi-drug resistant tuberculosis.

MDR-TB can develop when a patient being treated for another strain of TB does not complete the entire round of medication or fails to take the medication as prescribed. MDR-TB can be treated, however it is much harder to fight than regular TB and requires up to two years of long-term therapy. People with untreated MDR-TB are highly contagious and pose a significant health threat to those around them.

The vaccine known as BCG has been of some benefit in preventing TB, although it is not widely used in the United States and is usually administered in countries where TB is more common. For global travelers living in the United States an annual physical conducted by a healthcare provider can serve as a preliminary screen for tuberculosis symptoms. You can also request a quick and easy TB skin test at your annual physical, and this is an especially good idea if you’ve been traveling to parts of the world where tuberculosis is prevalent. Most importantly, if you are diagnosed with tuberculosis, be vigilant and conscientious about completing your course of treatment. In general tuberculosis is a preventable disease. The best way to control it is to diagnose and treat people with the infection before they develop active TB.