Tuberculosis Worldwide in 2017: 10 Million Cases, 1.57 Million Deaths, Slow Progress

Tuberculosis (TB) is the world’s leading cause of death from a single infectious agent, and the leading cause of death among people living with HIV, accounting for about 40% of their deaths. The United Nations’ Sustainable Development Goals and the World Health Organization’s End TB Strategy set targets for 2020–2035; the first milestones called for TB deaths to fall 35% and TB incidence 20% by 2020, compared with 2015.

WHO has estimated TB for every country each year since 2000. A team from CDC and WHO reviewed the estimates for 2017 to measure progress.

How the estimates are made

All 194 WHO member states report TB data each year. Where reported cases do not capture every new case, WHO draws on national prevalence surveys, inventory studies that measure underreporting, adjustments for under- and overdiagnosis, and expert judgment on gaps in detection. Deaths among HIV-negative people come from death registration, mortality surveys, or incidence multiplied by case fatality; deaths among people with HIV are estimated from incidence and case fatality.

The global picture in 2017

Incidence has fallen by an average of 1.5% a year since 2000. Among people with HIV, annual TB incidence fell from 4.5% in 2000 to 2.6% in 2016 and 2.4% in 2017.

Drug resistance — to at least rifampicin, or to both isoniazid and rifampicin — affected 3.6% of newly diagnosed cases and 18% of previously treated ones.

Estimated TB cases and deaths worldwide, 2000–2017, with uncertainty ranges. Image from CDC’s page.

Where TB strikes

WHO’s South-East Asia and Africa regions carried nearly 70% of the world’s TB. South-East Asia had more cases, but incidence was similar in both — 226 and 237 per 100,000 — and most high-incidence countries lay in these two regions.

The regions differ in what drives the disease:

• Africa, with the highest HIV prevalence, had 27% of its TB cases among people with HIV, and the highest TB case fatality.
• South-East Asia had just 3% of cases among people with HIV, suggesting that other factors, such as undernutrition or poverty, may drive its epidemic.
• Europe had relatively low incidence but by far the highest share of drug-resistant TB: 40% of cases, against 3.6%–6.3% in every other region.

Estimated TB incidence per 100,000 people by country, 2017. Image from CDC’s page.

Preventing TB disease

TB preventive treatment — most often daily isoniazid for at least 6 months — can stop people who may be infected from developing the disease. It is recommended for people with HIV, among whom isoniazid has been shown to cut deaths from all causes by 37%, and for all household contacts of patients with bacteriologically confirmed pulmonary TB (earlier, only for children under 5).

Uptake was slow. In the 67 countries reporting, about 960,000 people with HIV received preventive treatment in 2017 — 36% of those eligible, and barely more than the 930,000 of 2014. In 138 reporting countries, about 292,000 eligible children under 5 received it, 23% of those estimated to need it. The End TB Strategy aims for at least 90% coverage by 2025.

About a quarter of the world’s population is estimated to have latent TB infection and so to be at risk of disease later. Besides the traditional isoniazid course, new WHO guidelines support a 3-month, once-weekly isoniazid-rifapentine regimen (3HP) for adults and children; rifapentine costs substantially more, but the regimen is easier to complete and as safe and effective.

What it will take

The declines of 2017 were real but too slow to meet the 2020 milestones, and much faster annual reductions will be needed for the 2030 and 2035 targets. The authors call for:

• new approaches to finding cases;
• wider preventive treatment, especially for people at high risk;
• newer treatments — two oral drugs, delamanid and bedaquiline, have shown favorable efficacy and safety against drug-resistant TB, and the strategy aims for at least 90% coverage with new TB drugs by 2025;
• HIV prevention and control; and
• strategies matched to each region’s risk factors, from screening people with HIV to addressing poverty and malnutrition and treating drug-resistant TB.

The estimates are limited by the quality of the underlying surveillance data, and by the different methods used for different countries, which can make comparisons between regions and countries less exact.

Sources

Based on MacNeil A, Glaziou P, Sismanidis C, Maloney S, Floyd K, "Global Epidemiology of Tuberculosis and Progress Toward Achieving Global Targets — 2017," Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; written with the World Health Organization and rewritten in hubnx’s own words.