TB Disease vs. TB infection
In LA County, TBCP refers to “latent TB infection” as “TB infection” to encourage clinicians to take action once they diagnose TB infection in their patients. If a person with TB infection completes preventive treatment, their chance of developing TB disease is significantly reduced.5
TB disease most commonly presents as pulmonary TB, but in LA County in 2016, 17% of the cases of TB disease were extrapulmonary involving other organs such as the kidney, brain, and lymph nodes.7 TB is an airborne transmissible disease that spreads when a person with pulmonary TB disease coughs or sneezes and releases microscopic droplets with TB bacteria into the air and people sharing the same airspace inhale the infected droplets. Not all who are exposed to TB develop TB infection, and factors such as the length of time a person spends in the affected airspace, the amount of bacteria released into the air, and the immune system of the exposed person determine the likelihood of developing TB infection. On average, about one third of those who have a significant exposure to TB develop TB infection.8 Visit the CDC “Basics TB Facts” website for more information.
Interestingly, about 90% of people with untreated TB infection never develop TB disease, and currently there are no diagnostic tests that reliably predict who will progress to having TB disease. About 5% of people with newly acquired TB infection progress to TB disease within two years if left untreated. The other 5% with untreated TB infection who reactivate and progress to TB disease may do so many years and even decades after being infected. Medical conditions such as diabetes, HIV, cancer, active tobacco use, and renal disease as well as immunosuppressive medical therapies can increase the risk of reactivation of TB disease from TB infection.
Because there is no vaccine that protects people from being infected with TB, treatment of TB disease and TB infection are the only ways to eliminate TB. Countries with high rates of TB disease use the BCG vaccine to prevent young children from progressing from TB infection to disseminated TB, but individuals vaccinated with the BCG vaccine can still develop TB infection and TB disease.9