Skepticum

Much has been discussed recently in the news about TB. One of the things that hasn’t been mentioned much is the difference between TB infection and TB disease.

What is the difference between latent tuberculosis infection and tuberculosis disease?

Latent tuberculosis infection (LTBI) means the person has the TB germ in their body (usually lungs), but has yet to develop obvious symptoms. In latent TB, the person has a significant reaction to the Mantoux skin test with no symptoms of tuberculosis, and no TB organisms found in the sputum. Tuberculosis disease indicates the person has symptoms, a significant reaction to a Mantoux skin test and organisms found in the sputum. In order to spread the TB germs, a person must have TB disease. Having latent TB infection is not enough to spread the germ. Tuberculosis may last for a lifetime as an infection, never developing into disease. Source: New York State Department of Health.

So how does the disease spread?

A person with TB disease may remain contagious until he/she has been on appropriate treatment for several weeks. However, a person with latent TB infection, but not disease, cannot spread the infection to others, since there are no TB germs in the sputum. Source: New York State Department of Health.

Another factor in the spread of TB has to do with length of exposure. On Oct. 5, 1994 the Journal of the American Medical Association published an article by CDC’s Cynthia R. Driver and her colleagues. The article documented a case of infectious TB caught in flight. A flight attendant diagnosed with active pulmonary TB worked on 167 flights while contagious. 30% of the crew she worked with but only 6.7% of the passengers later tested positive on the tuberculin skin test (only 2 of the crew had been tested for TB previously and tested negative, thus there is not way to positively associate all infections to the flight attendant).

“The authors conclude that the risk of TB was associated with the length of time the crew members and passengers were exposed to the infectious flight attendant.”

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