Tuberculosis control in Vietnam

GLOBAL EPIDEMIOLOGY OF TUBERCULOSIS: BURDEN OF DISEASE The World Health Organization (WHO) declared tuberculosis (TB) a global public health emergency in 1993 [1]. About one third of the world’s population is infected with Mycobacterium tuberculosis (M. tuberculosis). It is estimated that, in 2005, there were 8.8 millions new cases of tuberculosis, of which 3.9 million were smear-positive and 11% were in adults infected with the human immunodeficiency virus (HIV) ), as well as 1.6 million TB deaths worldwide. More than 80% of all TB patients in 2005 lived in Asia and SubSaharan Africa [2]. In 2005, the TB incidence rate was stable or in decline in all six WHO Regions. However, the total number of new TB cases was still rising slowly [2]. Today, TB is still one of the world’s leading causes of death and of the global burden of disease. It is estimated that between 2002 and 2020, approximately 1,000 million people will be newly infected, over 150 million will become sick and 36 million will die of TB if proper control measures are not instituted [3]. Poverty, HIV and multidrug-resistant tuberculosis (MDR-TB) are key factors driving the TB epidemic. TB is principally a disease of poverty, 95% of TB all cases and 98% of deaths from tuberculosis are in developing countries [4]. Vulnerability to active TB has been strongly correlated with the conditions and consequences of poverty, such as malnutrition, inadequate and overcrowded housing, and unsanitary working conditions [5-12]. As 75% of TB cases in developing countries are people in their most economically productive age groups (15-50 years) [13], a vicious circle ensues in which, TB itself is a cause of poverty. The greatest emerging threat to TB control arises from the HIV pandemic. During 2005 alone, an estimated 2.8 million persons died from AIDS, 4.1 million were newly infected with HIV, and 36.6 million were living with HIV [14]. HIV may alter the epidemiology of tuberculosis in several ways [15]. HIV promotes progression to active TB both in people with recently acquired (16) and with latent [4,17] M.tuberculosis infection. HIV infection is the most powerful risk factor recognized in the progression to active disease from pre-existing infection with M. tuberculosis [18]. HIV increases not only the risk but also the rate of progression of recent or latent M. tuberculosis infection to disease [19-21]. HIV also increases the risk of recurrent TB after successful TB treatment [22]. Persons co-infected with HIV and M. tuberculosis have a five to ten-fold increased risk of developing active TB compared to those infected with M. tuberculosis alone [17]. Increasing tuberculosis incidence in people living with HIV/AIDS (PLHA) poses an increased risk of TB transmission to the general community, whether or not HIV-infected [23]. Over time, the greater risk and propensity to develop active TB among HIV-infected persons, particularly in countries of high TB burden, can lead to rapid increases in TB incidence and prevalence. TB, although preventable and treatable, is one of the most common causes of morbidity and mortality among PLHA worldwide [24-30]. By the end of 2000, of the 11 million people worldwide were co-infected with M. tuberculosis and HIV, with 71% of those co-infected living in sub-Saharan Africa and 22% living in South-East Asia [31]. HIV fuels the TB epidemic where the population infected with M. tuberculosis overlaps with the population infected with HIV. In many countries of Africa and Southeast Asia, infection with HIV resulted in a rapid increase of TB morbidity and mortality [32-34]. HIV prevalence in tuberculosis patients is less than 1% in the Western Pacific region but 38% in Africa [24]. In countries with the highest HIV prevalence, more than 75% of cases of TB are HIV-associated [2]. In addition to HIV-associated TB, multidrug resistant tuberculosis (MDR-TB) is an increasing threat. Data from the global reports on resistance to anti-TB drugs have shown that drug resistance is present worldwide [37-42] with an estimated 424,203 new cases of multidrug resistance TB (MDR-TB) - which are resistant to at least the two most powerful first-line drugs (isoniazid and rifampicin) – in 2004 [40,41]. Most MDR-TB cases are found in three countries – China, India and the Russian Federation – accounting for 62% of the estimated global burden [41]. The prevalence of resistance among previously untreated patients reflects programme performance over a long period of time, and indicates the level of transmission within the community [40]. Outbreaks of multidrug-resistant tuberculosis have been reported from both industrialized and developing countries in patients with HIV infection [37-40]. HIV itself does not cause nor promote the development of multidrug resistance, but it fuels its spread by accelerating the progression from infection to disease [43]. The cost of detecting and treating of MDR-TB was 10- to 100-fold higher than susceptible TB patients. Even when second line drugs are available, the course of treatment takes much longer (18-24 months), its efficacy is lower and adverse reaction rates are higher [44]. In September 2006, the WHO has expressed concern over the emergence of virulent drugresistant strains of tuberculosis: extensively drug-resistant tuberculosis (XDR-TB) which accounted for on average 10% of the detected MDR-TB case [45]. XDR-TB is TB that is resistant to at least isoniazid and rifampin among the first-line anti-TB drugs (which is the definition of MDR-TB), and in addition to that to any fluoroquinolone and to at least one second-line injectable drug (amikacin, capreomycin or kanamycin) [46]. XDR-TB makes treatment nearly impossible with currently available anti-TB drugs and has extremely high mortality rates. Data from South Africa (2006) showed that out of 1,539 TB cases diagnosed between January 2005 and March 2006, 542 were culture positive, 221 were MDR and 53 XDR cases. Out of 53 “possible” XDR patients, 52 (98%) died with a median survival from sputum collection of 16 days (range 2-210 days) [47-50].