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Study Finds that Nearly One in Four Are Infected with Latent Tuberculosis

NOV 08, 2016 | EINAV KEET
The recent Global Tuberculosis Report 2016 released by the World Health Organization (WHO) acknowledged that the worldwide tuberculosis (TB) epidemic is even larger than previous estimates suggested. In a recent study that highlights the scope of TB, researchers from the United Kingdom found that nearly one-quarter of the world’s population is infected with latent TB.
According to WHO, TB infections impacted 10.4 million people in 2015, killing 1.8 million of those infected. Approximately 170,000 of those who died were children. India, Indonesia, China, Nigeria, Pakistan, and South Africa carry the greatest burden of TB and make up 60% of all cases globally. As deadly as TB infections caused by Mycobacterium tuberculosis (Mtb) can be, the majority of individuals who become infected never go on to have symptoms and instead experience what is known as latent TB (LTBI). Individuals with latent TB are likely to not be aware of the fact that they carry the bacteria, as they do not suffer from a bad cough, chest pain, fatigue, weight loss, or other symptoms that mark TB disease, and they cannot transmit TB to others. Latent infections can be diagnosed through a skin or blood test, and despite the lack of symptoms, people with latent TB still need to undergo an antibiotic treatment regimen that can last between three and nine months in order to prevent the onset of active disease.
Of those with latent TB, 5% to 10% will go on to develop TB disease at some point in their lives, most often within the first two years of Mtb infection. Researchers from the London School of Hygiene and Tropical Medicine and the University of Sheffield in the United Kingdom recently studied worldwide rates of LTBI, and their findings were published in the open-access journal, PLOS Medicine. They conducted their study in support of WHO’s End TB Strategy, the agency’s global plan to cut TB-related deaths by 95% and TB cases by 90%, all by the year 2035.

Using a combination of country trends and historical demographic data, the researchers estimated infection risk for 168 countries. They assessed the size and worldwide distribution of LTBI, studying scenarios that seek to answer questions such as: what number of active TB cases would arise from the current pool of people with latent infections if all TB transmission stopped immediately? With data on skin test surveys and WHO estimates on TB prevalence, the study found that 1.7 billion people worldwide had LTBI in 2014, making up 23% of the global population. With the rate of latent infections that progress to active disease, currently 1% of the world population, or 56 million individuals, were infected in the last two years and are at high risk of developing TB disease, and 11% of those cases are believed to be with an isoniazid-resistant strain.

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