IMPORTANT NOTE
Active tuberculosis can be contagious while latent tuberculosis is not, and it is therefore not possible to get TB from someone with latent tuberculosis.
The main risk is that approximately 10% of these people (5% in the first two years after infection and 0.1% per year thereafter) will go on to develop active tuberculosis. This is particularly true, and there is added risk, in particular situations such as medication that suppresses the immune system or advancing age.
The identification and treatment of people with latent TB is an important part of controlling this disease. Various treatment regimens are in use for latent tuberculosis. They generally need to be taken for several months
Latent Disease
"TB Bacteria Are Spread Only from a Person with Active TB Disease ... In people who develop active TB of the lungs, also called pulmonary TB, the TB skin test will often be positive. In addition, they will show all the signs and symptoms of TB disease, and can pass the bacteria to others. So, if a person with TB of the lungs sneezes, coughs, talks, sings, or does anything that forces the bacteria into the air, other people nearby may breathe in TB bacteria. Statistics show that approximately one-third of people exposed to pulmonary TB become infected with the bacteria, but only one in ten of these infected people develop active TB disease during their lifetimes."[1]
However, exposure to tuberculosis is very unlikely to happen when one is exposed for a few minutes in a store or in a few minutes social contact. "It usually takes prolonged exposure to someone with active TB disease for someone to become infected.
After exposure, it usually takes 8 to 10 weeks before the TB test would show if someone had become infected."[2] "Depending on ventilation and other factors, these tiny droplets [from the person who has active tuberculosis] can remain suspended in the air for several hours. Should another person inhale them, he or she may become infected with TB. The probability of transmission will be related to the infectiousness of the person with TB, the environment where the exposure occurred, the duration of the exposure, and the susceptibility of the host."[3] In fact, "it isn't easy to catch TB. You need consistent exposure to the contagious person for a long time. For that reason, you're more likely to catch TB from a relative than a stranger."[4]
If a person had latent tuberculosis, they do not have active/contagious tuberculosis. Once exposed, people very often have latent tuberculosis. To convert to active tuberculosis, the bacteria must become active.
IMPORTANT NOTE
People have medical privacy or "confidentiality" and do not have to reveal their active tuberculosis case to family, friends, or co-workers; therefore, the person who gets latent tuberculosis may never know who had the active case of tuberculosis that caused the latent tuberculosis diagnosis for them. Only by required testing (required in some jobs) [5] or developing symptoms of active tuberculosis and visiting a medical doctor who does testing will a person know they have been exposed. Because tuberculosis is not common in the United States, doctors may not suspect tuberculosis; therefore, they may not test. If a person has symptoms of tuberculosis, it is wise to be tested
There is a shorter version and video here Latent TB short version
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