highest. In South America, the countries with the greatest rates of tuberculosis per 100,000 are Bolivia (30) and Guyana (18), with the remaining countries having less than 10:100,000. "One-third of the world's burden of tuberculosis (TB), or about 4.9 million prevalent cases, is found in the World Health Organization (WHO) South-East Asia Region." "About one-third of the world's population has latent TB, which means people have been infected by TB bacteria but are not (yet) ill with disease and cannot transmit the disease," and most of those cases are in developing countries. "In the US, over half of all active TB cases occur in immigrants. The reported cases of active TB in foreign-born persons has remained at 7000–8000 per year, while the number of cases in US-born people has dropped from 17,000 in 1993 to 6,500 in 2005. As a result, the percentage of active TB cases in immigrants has increased steadily (from 29% of all cases in 1993 to 54% in 2005)," and most of those cases are in developing countries. Controversy There is controversy over whether people who test positive long after infection have a significant risk of developing the disease (without re-infection). Some researchers and public health officials have warned that this test-positive population is a "source of future TB cases" even in the US and other wealthy countries, and that this "ticking time bomb" should be a focus of attention and resources. On the other hand, Marcel Behr, Paul Edelstein, and Lalita Ramakrishnan reviewed studies concerning the concept of latent tuberculosis in order to determine whether tuberculosis-infected persons have life-long infection capable of causing disease at any future time. These studies, both published in the British Medical Journal (BMJ) in 2018 and 2019, show that the incubation period of tuberculosis is short, usually within months after infection, and very rarely more than two years after infection. They also show that more than 90% of people infected with M. tuberculosis for more than two years never develop tuberculosis even if their immune system is severely suppressed. Immunologic tests for tuberculosis infection such as the tuberculin skin test and interferon gamma release assays (IGRA) only indicate past infection, with the majority of previously infected persons no longer capable of developing tuberculosis. Ramakrishnan told the New York Times that researchers "have spent hundreds of millions of dollars chasing after latency, but the whole idea that a quarter of the