By Dr Jay Desai
Although I have been living in the US for several years now, I continue to maintain close ties with India and this involves frequent and prolonged visits to the homeland. A key part of the planning for each of these trips is an effort to prevent transmission of diseases that are relatively more common in India to my young daughter. Apart from the usual vaccinations and weekly medications for prevention of malaria, an important intervention includes checking the TB skin test, also known as PPD (purified protein derivative) test. This test is recommended for those living in the US and many other developed countries after travel to regions where TB is endemic or upon exposure to a contagious TB patient. A strongly positive test usually (not always) means that one is infected. It does not necessarily mean that there is TB disease. If the chest x-ray is negative and otherwise there are no symptoms or signs of TB, the infected person is usually considered disease free. This state of being infected but without disease is also called latent TB infection. Apart from the TB skin test, there are other forms of testing which can be used to assess for latent TB infection.
In many developed countries including in the US, latent TB infection is usually treated with anti-TB medication(s) to decrease the risk of its progression to disease over a person’s lifetime. Fewer medications for shorter duration are required for treatment of latent TB infection when compared to TB disease. Tools have been developed which predict lifetime risk of developing disease for those who have been infected based on various factors including age, geographic location and other co-morbid conditions such as malnutrition, diabetes mellitus and HIV. These tools also help assess the risk of developing side effects from TB medications. Treatment of those infected significantly decreases the likelihood of them developing disease for many subsequent years. Treating young children with latent TB infection is considered to be of paramount importance since they are more likely to progress to disease. Since most cases of contagious disease occur in adults, treating infected children is likely to decrease the possibility of them becoming potential adult transmitters in the future.
The guidelines in India recommend preventive medications for children less than 6 years who are known household contacts of a contagious TB patient. There are no specific strategies for implementation currently for latent TB infection in general. Indian Council of Medical Research and Ministry of Health and Family Welfare in recent years have put more emphasis on understanding latent TB infection in India. However, with research efforts directed mostly towards treatment of TB disease, latent TB infection remains relatively neglected. A search of the medical literature reveals very few original research articles or data out of India about latent TB infection.
India’s Revised National TB Control Programme in its 2012 annual report has mentioned that about 40% of Indians are infected with TB. To tackle its humongous TB problem, India needs to aggressively explore strategies to prevent TB disease as much as ensuring its effective treatment. Treating latent TB infection and thus preventing its progression to disease has worked very well for many developed countries and kept TB at bay. India needs to quickly figure out whether this approach (or at least a modified targeted one) would be feasible, safe and efficacious in Indian conditions. (The author has cared for children with TB in India for several years. He is currently a faculty at the University of Southern California Keck School of Medicine)