PREVALENCE OF TUBERCULOSIS

An Investigation into the Effect of Immigration and Ethnicity on Prevalence of Tuberculosis in West Midlands, UK

Chapter One: Introduction

Introduction

Tuberculosis is among the top ten causes of global mortality. It has been estimated that approximately one third of the world's population is infected with the tuberculosis bacillus, and that each year 8 million people develop tuberculosis disease and 1.8 million die of the disease. Approximately 80% of tuberculosis cases are found in 23 countries; the highest incidence rates are found in USA. The tuberculosis situation has worsened over the past two decades in USA owing to the HIV/AIDS epidemic, and in Eastern Europe in association with multidrug resistance, following deterioration of the health infrastructure.

Tuberculosis is caused by Myobacterium tuberculosis, a microorganism whose principal reservoir is humans. M. tuberculosis is spread by patients with pulmonary tuberculosis, especially those with positive sputum smears. Of those becoming infected, 10-12% will develop tuberculosis disease after a period ranging from weeks to decades. The risk of disease declines steeply with time after infection. Disease may also occur after reinfection.

In 2000, the G8 group of countries called for the scaling up of interventions against HIV, tuberculosis and malaria, and set a target for the reduction in tuberculosis mortality of 50% by 2010 (Watts, 78:1168). This target may be difficult to achieve despite the availability of the World Health Organization (WHO) directly observed treatment, short-course (DOTS) strategy for the treatment of tuberculosis, which is considered to be a very cost-effective health intervention with a large potential impact. Reasons are the slow epidemiology of tuberculosis and the slowness with which the DOTS strategy is being adopted.

After describing available tuberculosis interventions, we assess their effectiveness at the individual and population level, and the extent to which an additional impact can be expected from an expansion in tuberculosis control measures. This assessment is based mainly on a literature review. In addition, we provide cost-effectiveness estimates for different interventions using an extension of a model proposed by Styblo(Dye, 146-52), and explore constraints to the scaling-up of interventions. This paper is restricted to drug-susceptible tuberculosis. In countries where multidrug resistance is common, special measures are needed, which are discussed elsewhere. In settings with a high prevalence of HIV infection, HIV prevention will be of major importance for tuberculosis control. For a discussion of the effectiveness of these HIV prevention measures we refer to other reviews. Among tuberculosis patients with HIV, the risk of death is very high. Most of the deaths are attributed to HIV. While the present paper addresses tuberculosis treatment, it does not deal with measures such as antiretroviral treatment to reduce HIV-associated mortality.

Available Tuberculosis Interventions

The main components of the WHO DOTS strategy are political commitment, case detection among self-reporting patients with symptoms using sputum smear microscopy, short-course chemotherapy under proper management, including directly observed therapy, assurance of a regular drug supply, and a strong surveillance and monitoring system (Kochi, 18:225-32). The need for directly observed treatment as a universal requirement is controversial, since the success of some ...