Tuberculosis

Roughly one-third of the world’s population has been infected with M. tuberculosis, and new infections occur at a rate of one per second. However, not all infections with M. tuberculosis cause tuberculosis disease and many infections are asymptomatic. In 2007 there were an estimated 13.7 million chronic active cases, and in 2010 there were 8.8 million new cases, and 1.45 million deaths, mostly in developing countries. 0.35 million of these deaths occur in those co-infected with HIV.

Tuberculosis is the second most common cause of death from infectious disease (after HIV). The absolute number of tuberculosis cases has been decreasing since 2005 and new cases since 2002. China has achieved particularly dramatic progress, with an 80 percent decline in its TB mortality rate. The distribution of tuberculosis is not uniform across the globe; about 80% of the population in many Asian and African countries test positive in tuberculin tests, while only 5–10% of the U.S. population test positive.

In 2007, the country with the highest estimated incidence rate of TB was Swaziland, with 1200 cases per 100,000 people. India had the largest total incidence, with an estimated 2.0 million new cases. In developed countries, tuberculosis is less common and is mainly an urban disease. In the United Kingdom, the national average was 15 per 100,000 in 2007, and the highest incidence rates in Western Europe were 30 per 100,000 in Portugal and Spain. These rates compared with 98 per 100,000 in China and 48 per 100,000 in Brazil. In the United States, the overall tuberculosis case rate was 4 per 100,000 persons in 2007. In Canada, tuberculosis is still endemic in some rural areas.

The incidence of TB varies with age. In Africa, TB primarily affects adolescents and young adults. However, in countries where TB has gone from high to low incidence, such as the United States, TB is mainly a disease of older people, or of the immunocompromised.

Tuberculosis incidence is seasonal, with peaks occurring every spring/summer.The reasons for this are unclear, but may be related to vitamin D deficiency during the winter.

In Europe, deaths from TB fell from 500 out of 100,000 in 1850 to 50 out of 100,000 by 1950. Improvements in public health were reducing tuberculosis even before the arrival of antibiotics, although the disease remained a significant threat to public health, such that when the Medical Research Council was formed in Britain in 1913 its initial focus was tuberculosis research. (From Wikipedia, April 2014)