Epidemiology of Tuberculosis. Tuberculosis (TB) is an airborne infectious disease caused by a group of closely related bacterial species termed Mycobacterium tuberculosis complex (1). The incidence, prevalence, and burden of TB vary by country. Nonetheless, globally, TB is a major public health concern that accounted for approximately 1.7 million deaths and 10.4 million new cases in 2016 (2). Furthermore, approximately 23% of the world population has latent TB infection (LTBI), an asymptomatic condition that is not infectious (3). Although antimicrobial drugs can be used to treat active TB disease and prevent LTBI from developing into active TB disease, there have been growing concerns of multidrug- resistant (MDR) and extensively drug-resistant (XDR) TB transmission (4–6). MDR and XDR TB have been associated with poor treatment outcomes (7,8) In the United States, there has been a marked decrease in incidence of TB from 52.6 cases per 100,000 population in 1953 to 2.9 cases per 100,000 population in 2016 (1). The steady annual decrease in incidence was briefly interrupted from 1985 through 1992; the resurgence was associated with factors including infrastructure issues, increased immigration, congregate settings, and the human immunodeficiency virus (HIV) epidemic (9–11). Since 1993, the annual decrease has been greater than 0.2 cases per 100,000 persons. This decline slowed during 2013 to 2015 where case rates stagnated at approximately 3.0 cases per 100,000 population (12). The reported number of TB cases in 2016 demonstrated a 3.6% decrease from 2015 corresponding to a case rate of 2.9 per 100,000 persons (1). The reported incidence of TB rates varies between states, with nine states having rates above the national average. Among these states, four states including California, Florida, New York, and Texas accounted for more than half of the total cases in the United States. The rates of TB are higher for many U.S.-affiliated Pacific Islands which range from 1.8 cases per 100,000 in American Samoa to 243.9 cases per 100,000 in the Republic of the Xxxxxxxx Islands (1). Although drug resistance has become a concern for many countries, the percentage of TB cases that are drug resistant (including MDR and XDR TB) within the United States has remained stable for the past 20 years (1,4). A major risk factor for TB disease is travelling to or being born in countries with high rates of TB. In 2016, the rate of TB diagnosed in the U.S. among non-U.S.-born persons was
Epidemiology of Tuberculosis. Tuberculosis, a pulmonary infection caused by Mycobacterium tuberculosis (Mtb), remains a significant cause of mortality and morbidity globally. In 2007, 1.77 million deaths were attributed to Mtb, a figure surpassed only by deaths due to HIV infection (1). The disease is transmitted via exposure to inhaled droplets containing Mtb, with dispersal facilitated by talking, singing, coughing and sneezing (2). Of those who are exposed and infected, an estimated 5-10% will eventually develop active disease (3). Those who are asymptomatic, but harbor viable bacteria in their lung tissues, are considered to be latently infected; approximately one in three individuals worldwide is in this category (4). Domestically, the incidence of tuberculosis is declining. In 2010, the incidence of 3.6 cases per 100,000 population represented a 3.9% decrease from the previous year (5). While promising, the incidence among foreign-born residents highlights additional challenges. In 2010, the number of new TB cases among foreign-born residents was 11 times greater than for U.S.-born individuals (5). Globally, the distribution of Mtb is also unbalanced, as the majority of cases are found in 22 high-burden countries, largely in Asia and Africa. Nearly half of all cases annually are identified in China, Bangladesh, India, Indonesia and Pakistan (2). Assuming the current annual rate of reduction in incidence remains unchanged from 1%, the goal of tuberculosis elimination is unlikely to be achieved prior to 2050 (6). Better strategies and new drug regimens are needed to achieve greater success in the prevention and treatment of pulmonary tuberculosis.
Epidemiology of Tuberculosis. Tuberculosis is the 7th leading cause of global mortality and the 2nd most frequent cause of death from a single infectious disease agent, after the human immunodeficiency virus (HIV) causing acquired immune deficiency syndrome (AIDS) (27). TB causes an estimated 1.5 million deaths per year, with approximately 9.4 million new cases occurring annually, amounting to a global prevalence of 12 to 16 million people with active disease (1). One third of the world’s population (more than two billion persons) may be infected with bacteria that cause TB (1). The US is a low-TB incidence country, with a decreasing TB rate of 3.8 cases per 100,000 population in 2008, with civilian LTBI prevalence estimated at 4.2% (over 11 million) in 2000 (2, 5). The US military has a lower rate of reported pulmonary TB than the US average (0.65 cases per 100,000 persons from 1998 to 2007) (28). Even when adjusting for underreporting, the military’s low TB incidence (0.87/100,000 person-years) can be defined as a “low-incidence” population (29). Estimates of LTBI in the military, determined by TST reactivity, range from 1 to 5%, depending on the service branch (30). Despite the low incidence, military populations may still be at risk of Mtb transmission due to exposure to populations at increased risk of MTBI and congregate settings (31-33). Most TB is caused by M. tuberculosis, but other species of Mycobacterium may cause TB, including M. bovis, M. africanum, M. canettii, and
