While the most common form of tuberculosis (TB), which is pulmonary TB, infects the lungs, some 20% of TB infections develop in the lymph nodes, brain, gut, eyes, or other organs. Some of these organs have immune privileges in the body. This means that extra-pulmonary infections can persist even after the TB infection in the lungs is resolved. Just as we have an undercount of the people infected with TB, the public health challenge of extra-pulmonary TB (EPTB) may be larger than our current estimates.
The World Health Organization (WHO) reports over 10 million new cases of TB every year and India alone accounts for 27% of the global TB burden. However, the burden of EPTB is hard to estimate. EPTB is often stain negative, which means it is not detectable on regular TB stain tests. The infection may surface in any part of the body and present itself like other non-TB conditions. Many cases of EPTB may not have a corresponding lung infection. So, EPTB’s true prevalence in society remains hidden.
As the burden of pulmonary TB is greatest, it makes epidemiological sense to focus our efforts on its elimination. The lungs are the primary source of infection spread and reducing this burden will impact all forms of the disease. However, given the scale of TB, variants like EPTB end up affecting a large number of people. EPTB’s under diagnosis results in irreparable damage to the infected organs, leading to vision loss or even blindness, for example. It is therefore important to address TB in all its complexity.
