Epidemiology

Global burden

In 2011, the global incidence of TB was estimated by the World Health Organization (WHO) to be 125 cases of TB per 100 000 people, which is equivalent to 8.7 million newly diagnosed patients (incident cases). Of the 8.7 million new cases, 12–14% (i.e. 1.0–1.2 million people) were HIV positive; these people were mainly African (79% of the total TB/HIV co-infected individuals). The total number of people with TB (prevalent cases) in 2010 was estimated to be 12 million (range 10–13 million), equivalent to 170 cases per 100 000 people globally. The number of prevalent cases has trended downwards since 1990; the same is true for the incidence of new cases, although there was a slight increase in the latter at the beginning of the 21st century.

The total number of patients dying of TB in 2011 was estimated to be 1.4 million (range 1.3–1.6 million), corresponding to a rate of 20 deaths per 100 000 people. The mortality rate of TB patients who were HIV negative was 14 per 100 000 in 2011 (a mortality rate of 15%), equivalent to an estimated 990 000 deaths (range 840 000–1.1 million); an estimated 430 000 HIV-positive people with TB (range 400 000–460 000) died in the same year (a mortality rate of 39%).

Epidemiology in Europe

In 2011, the estimated incidence of TB in the WHO European region was 42 per 100 000 people, with an estimated total of 380 000 incident cases. Overall, the TB notification rate has declined since 2007, from 56.3 per 100 000 inhabitants to 42 per 100 000 in 2011, a decrease of 27%.

The four countries with the highest TB notification rates (which include both incident cases and people who have relapsed) in the WHO European region in 2011 were Kazakhstan, Moldova, Georgia and Kyrgyzstan, with 118, 119, 105 and 103 cases per 100 000 inhabitants, respectively. A TB notification rate of 50–100 per 100 000 inhabitants was reported in seven states, including several former Soviet Union countries; the 11 countries with new/relapsing case-notification rates above 50 per 100 000 account for about 76% of the total number of notifications in Europe. Conversely, 32 western and central European nations notified less than 20 cases per 100 000 inhabitants. Estimated TB incidence is detailed in figure 1.

26% of notified TB cases in the European Union (EU)/European Economic Area (EEA) were foreign-born; in Israel, Norway and Sweden, this proportion was more than 85% of the total (figure 2). More than two-fifths (41%) of newly notified patients were 25–44 years of age. 16 countries reported a male-to-female ratio of > 2, due to males being more exposed to risk factors for developing TB such as HIV infection, smoking, alcohol abuse and homelessness.

In 2011, 12 751 (56.5%) European patients co-infected with TB and HIV were detected, out of an estimated 22 554 coinfected cases in the WHO European region. The proportion of TB cases with HIV infection among all TB cases tested for the virus in the WHO European Region is increasing by 20% per year (from 2.8% in 2006 to 6.5% in 2011). TB/HIV co-infected patients made up more than 10% of the total TB notifications in Luxembourg (40%), Ireland (20.2%), Ukraine (18.5%), Malta (16.7%) and Estonia (15%) (figure 3).

The estimated TB prevalence in Europe in 2011 was 55.9 cases per 100 000 inhabitants, corresponding to 502 763 patients. There is a strong gradient from East to West, and non-EU/EEA countries showed sharply higher rates than EU/EEA countries (104.4 versus 18.4 cases per 100 000 inhabitants, respectively).

The overall estimated TB mortality rate in Europe in 2011 was 4.9 deaths per 100 000 inhabitants, equivalent to 44 304 deaths in total; it was much higher in non-EU/EEA countries than in EU/EEA countries (10.1 versus 0.9 per 100 000 inhabitants, respectively) (figure 4). Among the EU/EEA member states, only Lithuania and Romania had death rates higher than 5 per 100 000 inhabitants, whereas more than 10 people per 100 000 inhabitants died of TB in Kyrgyzstan, Kazakhstan, Russia, Tajikistan, Moldova and Ukraine.

Drug-resistant tuberculosis

An important epidemiological and public health issue is the global emergence and spread of multidrug-resistant TB (MDR-TB), caused by M. tuberculosis strains resistant to at least isoniazid and rifampicin, the most efficacious anti-TB drugs. In 2006, an even more severe form of drug-resistant TB was described in several settings; this was defined as extensively drug-resistant TB (XDR-TB), caused by MDR-TB strains resistant to any fluoroquinolone and to at least one injectable second-line drug (kanamycin, capreomycin, amikacin).

The WHO estimated that the global prevalence of MDR-TB cases in 2011 was 630 000. 27 countries were classified as ‘high MDR-TB burden’ countries, the top 13 of which were states of the former Soviet Union. Belarus and Kazakhstan reported the highest MDR-TB prevalence among both new and previously treated TB cases. Overall, the highest proportions of MDR-TB among both new (15.1%) and previously treated (44%) TB patients were detected in Europe out of all WHO regions; however, the burden of MDR-TB among previously treated TB cases was unequally distributed, being greater than 50% in Belarus, Estonia, Kazakhstan, Moldova, Russia, Tajikistan, Ukraine and Uzbekistan.  Figure 5 shows the proportion of notified MDR-TB cases. Almost 12% of MDR-TB cases had XDR-TB. Unfortunately, drug-susceptibility testing (DST) to ascertain MDR-TB status is carried out worldwide in less than 4% of new TB cases and 6% of previously treated cases; furthermore, treatment tailored to MDR-TB was started in only 23% of confirmed MDR-TB cases globally in 2011.

See the entire Tuberculosis Chapter