The World’s Burden of TB

Each year, the World Health Organization (WHO) determines the number of new TB cases (incidence), existing TB cases (prevalence), and TB deaths (mortality) within the world's population. This agency reported 8.6 million new cases of tuberculosis across the globe last year, and their distribution among the world's nations is presented in the map below.

Of last year's 8.6 million new TB cases, 60% lived on the continent of Asia while another 25% were in Africa. The WHO has designated 22 countries as "high burden" and these nations are a priority for its diagnosis and treatment efforts. These are identified within the map above by their numerical burden ranking and their case numbers are listed in the table below.

Over 80% of all new TB patients reside within this group of 22 countries, with the top five members alone accounting for more than half of the global total. By comparison, the United States and the United Kingdom reported 11,000 and 9,400 new cases of tuberculosis over the past year, respectively.

The Rising Threat of Drug-Resistant TB

A patient who is found to have an active case of tuberculosis is initially treated with four antibiotics simultaneously: isoniazid, rifampin, ethambutol, and pyrazinamide. This regimen is administered daily for six months (preferably under direct observation to ensure compliance), has a cure rate of 90% in HIV-negative cases, and can cost as little as $50 when procured through the Global Drug Facility of the Stop TB Partnership. By combining four drugs in this manner, it increases the likelihood that a partially resistant strain within a patient will be killed and that the treatment itself will not lead to further antibiotic resistance.

In the event that a resistant infection has been detected, one or two of the ineffective medications will be replaced by second-line tuberculosis treatments. These drugs tend to be less effective, more toxic, far more expensive, and require a longer duration of therapy. Drug-resistant strains of Mycobacterium tuberculosis bacteria typically fall into one of two classifications, multidrug-resistant tuberculosis (MDR-TB) or extensively drug-resistant tuberculosis (XDR-TB), where the latter includes strains thought to be resistant to all known antibiotics. The drug resistance profiles and treatment options for these two groups are compared with drug-sensitive TB in the table below.

An estimated 450,000 people around the world developed MDR-TB during the past year, representing 4% of all newly diagnosed TB cases and 20% of all previously treated cases, while another 170,000 died from it. Ten percent of these MDR-TB cases were in fact XDR-TB, and 92 countries had reported at least one case of XDR-TB by the end of last year. The WHO has identified 27 high MDR-TB burden countries which together accounted for 90% of the new drug-resistant tuberculosis cases reported worldwide in the previous year. These are identified within the map below, and their burden ranking and case numbers are listed in the table which follows.

While the nations of southeast Asia may produce more actual cases of MDR-TB due to their greater population densities, the republics of the former Soviet Union have a far higher prevalence, given the global rate of 4%. However, in all of these countries only a small fraction of drug-resistant infections are being diagnosed and treated according to international guidelines. Fully 350,000 of the 450,000 people who developed MDR-TB over the past year had cases that went both undetected and untreated.

The Twin Epidemics of TB and AIDS

TB patients who are also infected with HIV are thirty times more likely to die of their illness due to the latter's ability to destroy the human immune system. Death in untreated individuals is also greatly accelerated, typically occurring in less than six months. The emergence of HIV-AIDS in the 1980s has had devastating consequences for victims of the millennia-old global epidemic of tuberculosis, such that 1.1 million (13%) of the 8.6 million new TB cases and 320,000 (25%) of the 1.3 million TB deaths occurring over the past year were in HIV-positive individuals. The extent of overlap between these two great pandemic plagues is shown in the map below, where the rate of HIV coinfection within last year's new TB cases is given for each country.

Seventy-five percent of all HIV-positive TB patients can be found on the continent of Africa, and the nine countries reporting the highest percentage of HIV-AIDS within new tuberculosis cases over the past year were all located at its southern end:

Key to managing this crisis has been the rapid assessment of HIV status in newly diagnosed TB patients followed by the timely initiation of antiretroviral therapy in those who are HIV-positive. The percentage of TB patients with a documented HIV test result has risen steadily in recent years and now stands at 46% globally and 74% in Africa, where the two epidemics converge. Worldwide, the number of HIV-positive TB patients that have been placed on antiretroviral therapy continues to climb but is still only 57%.

Progress in the Fight Against TB

P. C. Weber's Hanging by a Thread series opens in the 1990s, when the decades-long trend of declining tuberculosis incidence suddenly and alarmingly reversed itself and prompted a massive response from the global health community. This included the declaration of TB as a global health emergency by the WHO (1993), the establishment of the Stop TB Partnership (2000), the implementation of the Global Drug Facility (2001), and the release of the Global Plan to Stop Tuberculosis (2006). Surveillance data published annually by the WHO clearly reveal the positive impact that these steps have had on controlling the epidemic:

The dramatic reductions in infection and death rates seen during the past ten years (panel A) are somewhat offset by the actual case numbers from the same period of time (panel B). This is due to explosive growth in the world's population from 5.3 billion in 1990 to 7.1 billion today, mostly in areas where TB is endemic. Still, remarkable progress has been made:

Prevalence: The rate of existing tuberculosis cases has decreased steadily since the late 1990s, resulting in a decline in global disease burden of 37% over that time. A total of 56 million people have been successfully treated since 1995, with 22 million lives saved.

Incidence: The rate of new tuberculosis cases began to drop for the first time in 2001 and has now been reduced by 18%. Similarly, the number of new TB cases per year reached its zenith in 2003 at 9.3 million and has now fallen to 8.6 million.

Mortality: The death rate from tuberculosis has been reduced by 45% since 1990. The number of TB deaths per year peaked in 2001 at 1.4 million and is today under one million (but doesn't include 320,000 annual deaths from TB in HIV-positive individuals).

Additional Information on TB

Buy a book and help fight TB: All profits from LGC Publishing's e-books (catalog) are donated to the Stop TB Partnership (website). Titles by F. Scott Fitzgerald and P. C. Weber are priced at just 99¢ and are available in over 50 countries around the world.

Text credits: All text in TB: Snapshot of an Epidemic was by P. C. Weber and employed raw data from the following sources: 2013 WHO Global Tuberculosis Report (download), 2013 UNAIDS Report on the AIDS Epidemic (download), and the WHO Global Health Observatory TB Data Repository (website).

Image credits: All maps, tables, charts, and images in TB: Snapshot of an Epidemic were by P. C. Weber. The first-line TB drugs chart also contains formulation images from Drugs.com and chemical structure images from Wikimedia Commons, and the animated title banner includes photographs of actual TB patients from the image library of the World Lung Foundation (website).