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Dear Doctors: I was surprised when I had to take a TB test for a new job and was shocked that it came back positive. I have no symptoms and feel fine. How did you get it? Could I have infected my family? I never realized that TB was widespread enough in the United States to automatically have to test for it.

Dear Reader: Tuberculosis, or TB, is a disease caused by bacteria known as Mycobacterium tuberculosis. When someone with an active infection coughs, sneezes, or cries, they release tiny particles of moisture called “droplet nuclei,” which contain the bacteria. These droplets are tiny enough that they can drift on an air current, move around a room, and stay suspended for several hours. This makes the disease highly contagious. If someone inhales these droplets, the TB bacteria they contain can reach the lungs, a favorable environment in which they can begin to grow. They can also settle in the lymph nodes and cause tuberculosis of the throat.

Symptoms of TB include fever, weight loss, night sweats, and a wet cough that can produce bloody phlegm. If an active TB infection is left untreated, the bacteria can travel through the bloodstream and infect other tissues, including the kidneys, spine, or brain.

When a person tests positive for TB but has no symptoms, as in your case, it is called latent TB. This means that as long as the bacteria is in your body, it is in small quantities and does not make you sick yet.

A person with latent tuberculosis is not contagious. They cannot transmit the disease. However, in some people, latent tuberculosis will develop into an active infection, known as tuberculosis disease. It can take up to two years or more. For this reason, anyone with latent tuberculosis should receive antibiotic treatment to eliminate the bacteria from the body.

Tuberculosis is a serious threat to international health. Worldwide, up to 10 million people develop active TB infection each year and 1.5 million die from it.

In the United States, thanks to vigilant testing and treatment, the disease is not as widespread. But that wasn’t always the case. At the start of the 20th century, tuberculosis was one of the leading causes of death in the United States. Historical reports from this time place the number at over 150,000 deaths per year due to tuberculosis.

Thanks to intensive detection, treatment and prevention efforts, as well as the development of the antibiotic streptomycin in 1943, the United States was able to reverse the trend. According to the Centers for Disease Control and Prevention, the United States recorded 7,800 active tuberculosis infections last year and about 500 deaths. Keeping these numbers low is why many employers require testing for TB.

Unfortunately, despite this remarkable turnaround, significant challenges remain. This includes the increase in drug-resistant strains of the bacteria, which are unaffected by isoniazid and rifampin, the main antibiotics used to fight the disease. All of this makes it important for you to seek immediate medical attention for your latent TB infection and to follow the drug treatment exactly as prescribed.

Send questions to [email protected], or write to: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Due to volume of mail , no personal answer can be provided.

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