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This Week in The Lancet

  • Volume 377 1719 (2011)
  • May 21, 2011

The global burden of tuberculosis

Tuberculosis (TB) is an extensively prevalent, preventable and treatable infectious disease causing great health and financial burden. TB ranks among the top ten causes of death worldwide and in 2007 alone caused 1.8 million deaths (1). The present era has provoked further concerns with the advent of multi-drug resistant strains of Mycobacterium tuberculosis. In recognition of its significance the World Health Organisation declared tuberculosis a Global emergency in 1994 (2). This article reviews the differences in the burden of tuberculosis between the developed and the developing world and highlights the present challenges of this global menace.

Epidemiological Burden

Approximately 2 billion people across the globe are estimated to be infected with the bacterium, of which 10% are likely to become symptomatic during their lifetime (3). The burden of TB is considerably greater in developing countries compared to the developed ones. For instance the prevalence rate per 100,000 population according to the World Health Organisation (WHO) report of 2009 is diagrammatically illustrated below. (4) 

fig1

The top twenty countries most affected by TB are developing countries and account for four-fifths of all cases. Furthermore, the number of cases in all regions increased during 1995-2005 other than those with established market economies (5).

Incidence

The incidence of TB has increased in the last two decades in the African continenhat from 170 cases to 350 per 100,000 population. In contrast, it has almost halved in the American continents (4). The trend in the South-East Asian, Western Pacific and Eastern Mediterranean have been fairly consistent, whereas Europe has shown a decline in the incidence of TB. 

fig2

Incidence per 100, 000

Mortality

The disparity between the prosperous world and its underprivileged counterparts is clearly evident in the mortality statistics for TB. Thus the annual mortality of TB is greatest in Africa (544,000 deaths/ 74 per 100,000 population) and South- East Asia (512,000 deaths/31 per 100,000 population).

These statistics are in striking contrast to Europe (66,000 deaths/ 7.4 per 100,000 population) and the American continents (49,000 deaths/ 5.5 per 100,000 population). (5) The present threat of TB is in terms of extra-pulmonary manifestations of disease, with increasing resistance seen to conventional anti-tuberculous drugs (Multi-drug-resistant TB) and co-infection with Human Immuno-deficiency (HIV) virus. 

fig3

Mortality per 100, 000

Extrapulmonary TB

The major risk factor predisposing to extra-pulmonary TB is immunosuppression, which is evident from the fact that the occurrence of extra-pulmonary TB has risen since the arrival of HIV/AIDS. More than half of patients with co-existing HIV and TB infection have extra-pulmonary involvement (6). Bones, lymph nodes and pleura are the most common sites of involvement. The Infectious disease society of America, American thoracic society and Centres for disease control and prevention recommend screening of HIV infection in tuberculosis patients (7).
The most prevalent site for extra-pulmonary TB is Lymph nodes (6). Cervical lymphadenitis is predominantly seen though other groups such as inguinal and axillary may also be involved. The Spine is the first site in which the involvement of the skeletal system is seen. In extra-pulmonary tuberculosis, arthritis and osteomyelitis may spread to other sites (8).

Meningitis is the chief presenting complaint in CNS involvement and intra-cranial Tuberculomas. The latter may manifest itself as space-occupying lesions. Extrapulmonary TB is indicated by a history of travel or habitation in an area of high risk, the presence of ascites with lymphocyte elevation and negative bacterial cultures and pericardial effusion when other causes have been excluded.

TB and HIV

Epidemiological studies suggest an increased incidence and prevalence of HIV in TB burdened regions of the world. South Africa, in which TB is the single most frequent cause of natural death, constitutes 0.7% of the world population and is home to 17% of the world’s total HIV population (9). Facts from 2008 show that of those infected with TB in Africa, 45% were co-infected with HIV, whereas the corresponding figures in Europe were just 3% (4). Conversely TB is the most prevalent infection in persons suffering from HIV (10). The co-existence of TB and HIV has caused serious threats in hampering the spread of two infections. Immunosuppression due to HIV leads to reactivation of latent TB whereas TB itself causes an increase in viral load of HIV causing increased morbidity and mortality (11).

The Way Forward

The facts elucidated above demonstrate the disparity of the TB burden in the developing nations compared to their prosperous counter-parts. There is a prompt need to act speedily and effectively to address and control the menace.

In 2008, it was estimated that the global annual expenditure pertaining to TB would be 3.8 to 5 billion dollars. In addition, 1.3 billion dollars were expected to be spent for drug-resistant TB. Out of these, just one-third, i.e. approximately 1.7 billion dollars were expected to be spent by the developing countries (12). Thus, the regions with the greatest proportion of the disease spent only modest sums compared to the affluent societies. This is due to the paucity of economic resources in such nations. For instance, the government of Pakistan’s health expenditure per person annually is just around 10 US dollars, whereas the international average is 434 US dollars (13). This necessitates the need for enhancing the funds for the health sector. In addition to this, prioritization of the health problems, education of the masses, efforts to reduce the spread of disease from infected individuals, provision of effective treatment to the affected persons, identification and reduction of multi-drug resistant strains of Mycobacterium tuberculosis and collaboration between the governmental and the private sectors in the above measures are some of the methods which can curtail the hazard to prevent the suffering of future generations.

Haris Riaz
Final year student
Dow Medical College, Karachi, Pakistan
harisriaz73(a)yahoo.com

References

1. Shen X, Deriemer K, Yuan Z, Shen M, Xia Z, Gui X, Wang L, Mei J, “Deaths among tuberculosis cases in Shanghai, China: who is at risk? BMC Infect Dis v.9;2009

2. TB —a global emergency. WHO report on the tuberculosis epidemic, 1994.Geneva: World Health Organization;1994. (Accessed on 5/9/2009)

3. Corbett EL, Watt CJ, Walker N, et al. The growing burden of tuberculosis: Global trends and interactions with the HIV epidemic. Arch Intern Med. 2003;163:1009–21.

4. WHO report on Tuberculosis, 2009. Available at URL http://www.who.int/tb/publications/global_report/2009/update/a-1_full.pdf Accessed on 27-7-2010

5. WHO Report on Global Tuberculosis control, 2001.WHO/CDS/TB/2001.287 (Accessed on 28/8/2009) Rieder HL, Snider DE Jr, Cauthen GM. Extrapulmonary tuberculosis in the United States. Am Rev Respir Dis 1990;141:347-51.

6. Blumberg HM, Burman WJ, Chaisson RE, et al. American Thoracic Society/Centers for Disease Control and Prevention/ Infectious Diseases Society of America: treatment of tuberculosis.Am J Respir Crit Care Med 2003; 167:603-62.

7. Golden M. Extra-pulmonary Tuberculosis: An overview. American Family Physician 2005. Am Fam Physician. 2005 Nov 1;72(9):1761-8. Review

8. Karim SSA, Churchyard GJ, Karim QA, Lawn SD: HIV infection and tuberculosis in South Africa: an urgent need to escalate the public health response. Lancet. Author manuscript; available in PMC 2010 January 7.

9. Alexander PE. De P. The emergence of extensively drug-resistant tuberculosis (TB): TB/HIV coinfection, multidrug-resistant TB and the resulting public health threat from extensively drug-resistant TB, globally and in CanadaCan J Infect Dis Med Microbiol. 2007 September; 18(5): 289–291.

10. Goletti D, Weissman D, Jackson RW, et al. Effect of Mycobacterium tuberculosis on HIV replication. Role of immune activation. J Immunol. 1996;157:1271–8. Available at URL: (Accessed on 20/9/2009) http://www.globalhealth.org/images/pdf/gho/2008_id_expenditures.pdf

11. Zubair M H, Zubair M M, Riaz H. rota virus mortality: A dilemma for the developing world. J Pak Med Assoc. 2009 Aug;59(8):582.

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