Tuberculosis 1: exploring the challenges facing its control and how to reduce its spread

Author

Miles Jarvis, MA, BSc, DipHE, DipTropN, RN (adult), is TB specialist nurse, Royal Bournemouth Hospital.

Introduction

Although many people in the UK believe tuberculosis (TB) is a disease of the past, every day at least one person dies from it in the UK, even though it is fully preventable and treatable (British Thoracic Society et al, 2009).
TB has been described as the greatest killer in history, claiming more lives than any other infectious disease (Ryan, 1992). Although mostly curable, it causes approximately two million deaths each year (Pratt et al, 2005).

What is TB?

Tuberculosis is caused by a bacterium that belongs to the genus Mycobacterium, and was discovered by Robert Koch in 1882 (Pratt et al, 2005). While there are many species of mycobacteria, a group of closely related species are collectively called the Mycobacterium tuberculosis complex. These are the causative agents of TB in humans.
People are infected by M. tuberculosis complex by one of three routes: inhalation (by far the most common route); ingestion; and inoculation (Pratt et al, 2005).
When people with infectious TB cough, talk, sneeze or shout, TB bacteria are forced into the air in respiratory droplets. These droplets evaporate quickly to leave a residue known as droplet nuclei, which are very small (1-5 nanometres in diameter). These are inhaled and, because of their size, can be drawn deep into the alveoli (Davies, 2003).
This can stimulate an immune reaction which may lead to the development of what is known as primary TB disease or, more commonly, to a latent TB infection, which may (or may never) activate into post primary TB later in life. The WHO estimates one in three people have a latent TB infection globally (Pratt et al, 2005).
Left untreated, a person with active (infectious) pulmonary TB will infect 10-15 people each year. The risk of a contact acquiring infection depends on the nature and duration of their exposure (Department of Health, 2004) - close household contacts are more likely to catch TB than acquaintances or work colleagues.
While the majority of TB cases are pulmonary, the proportion of non-respiratory disease is rising (Ormerod, 2008). Non-pulmonary TB accounts for 15-25% of reported cases; it commonly affects lymph nodes, bones and joints, the gastrointestinal or genitourinary tract, central nervous system, skin or pericardium. TB can also be miliary (disseminated through the bloodstream).

TB across the world

The severity of global TB led the World Health Organization to declare the disease a global emergency in 1993.
A Global Partnership to Stop TB was formed in 1998 and one of the United Nations Millennium Development Goals specifically identified the objective of halting the advance of the disease, and seeing its incidence reversed (WHO, 2008a).
The global number of new reported cases of TB is increasing, with 9.27 million reported in 2007, compared with 9.1 million in 2005 (WHO, 2009). However, with the exception of Africa, the incidence of TB per 100,000 population is stable or falling (WHO, 2008b). The increase in absolute numbers of new cases with a falling incidence rate is thought to be due to overall global population growth. The global incidence of TB seems to have peaked in 2004 (WHO, 2009).
Fig 1 shows the global incidence of TB. The highest is seen in sub Saharan Africa (343 per 100,000). There is a complex association with poverty, and greater incidence of TB occurs in low income countries. The condition perpetuates and exacerbates poverty, affecting countries economically and undermining development (Banavaliker, 2008). As Fig 2 shows, the greatest numbers of new cases are in China and the Indian subcontinent. India has one fifth of the world’s TB cases.
In the UK, TB is concentrated in urban areas, with London accounting for 39% of cases (Anderson et al, 2008). The rate in London is 44.3 per 100,000, while the UK rate is 14.1 per 100,000 (Health Protection Agency, 2009a). Over the past 20 years, the number of new cases of active TB reported per year has risen by almost three quarters. HPA data shows that TB cases rose by 2.9% in 2008 compared with 2007 (HPA, 2009b).

High risk groups

The increase in TB rates in the UK over the past two decades follows a change in epidemiology (Anderson et al, 2008).
In contrast to its occurrence in the general population in the first half of the last century, certain subgroups of the general population are at a higher risk of developing it (DH, 2004). High risk groups include:

• New immigrants from countries with high rates of TB;
• People with HIV infection;
• Those with a history of IV or heavy
• drug use;
• Prison populations;
• Homeless people;
• Those who are immunosuppressed;
• Refugees/displaced populations;
• Minority ethnic and marginalised groups;
• Occupational exposure (Pratt et al, 2005).

Controlling TB in the UK

In a high income country such as the UK with low TB incidence (from a global perspective), control focuses on:

• Early diagnosis and treating active cases;
• Preventing transmission;
• Active case finding;
• Treating latent infection (Sagebiel, 2008).

It is predicted that these activities will reduce the pool of TB in the population, prevent transmission of infection and help reduce the development of drug resistance.
Several documents have been published in the last five years on TB management and control in the UK, including a report from the chief medical officer for England, with 10 action points (DH, 2004) (Box 1).

Clinical guidelines

This action plan was followed by NICE (2006) guidelines for diagnosis and management. These, with guidance from the Joint Tuberculosis Committee of the BTS (2000; 1998), provide criteria for diagnosing, treating and controlling the condition. These were intended to introduce best practice and to standardise services (BTS et al, 2009).
Furthermore, the DH (2007) detailed how high quality TB services should be planned and commissioned. This document, known as “the TB toolkit”, is intended to offer a framework for implementing the action plan in line with NICE (2006) guidelines.
The BTS guidelines recognise the importance of TB nurse specialists’ role. They outline specific recommendations for the ratio of TB nurse specialists to people diagnosed with the disease (one full time nurse specialist with full clerical support per 50 notifications per year) (Joint Tuberculosis Committee of the BTS, 2000). This is a minimum standard; a ratio of 1:40 is recommended for London. The BTS et al (2009) report states that clinicians responsible for TB case management should be given clear guidelines to govern their workload, as there is no national standard.
The BTS and RCN set out to see what was happening at a local level regarding the implementation of the CMO’s action plan, by carrying out two surveys of TB lead consultants and TB nursing staff (BTS et al, 2009). While some results were encouraging in terms of the level of services, there were some areas where more effort is required if effective TB services are to be developed.
The findings reiterated the need to report TB incidence to the HPA. The use of multidisciplinary teams is advocated, particularly with HIV co-infected people. The report concludes that, despite the development of national guidance, TB control is not consistent across the country and activities are not well coordinated. However, some trusts and PCTs are responding well, and have established model services; this is encouraging if the CMO’s action plan (DH, 2004) is to be fully implemented (BTS et al, 2009).

TB and HIV

TB and HIV co-infection are a major global public health problem (Pozniak, 2008). TB is a leading cause of HIV related illness and deaths worldwide. In 2007, there were an estimated 1.37 million new cases of TB globally among HIV infected people and an estimated 456,000 of these died (WHO, 2008b). Worldwide, it is estimated that 8% of all new TB cases in adults are attributable to HIV infection (WHO, 2008b).
TB and HIV have been called “a cursed duet” because each aggravates the other. HIV infection significantly predisposes people to active TB, while active TB stimulates HIV replication. Highly active antiretroviral therapy (HAART) has significantly reduced the morbidity and mortality of HIV infected people, including those infected with TB. It is recommended that people being investigated for or diagnosed with TB are screened for HIV (British HIV Association, 2008).
In early HIV infection, the presentation of TB is typical of an infected person without HIV (Box 2) and upper lung zone infiltrates on chest X-ray. As HIV infection progresses, patients are more likely to present with disseminated disease (miliary TB) or with X-ray changes that can be mistaken for a bacterial pneumonia (Baggaley, 2008). Non-pulmonary TB is more common in people with HIV.

Drug resistance

A challenge to global TB control is drug resistance, which is increasing internationally and in the UK (Grant et al, 2008).
Certain strains of TB are resistant to one or more of the drugs commonly used to treat it (Pratt et al, 2005). Strains that are resistant to the most important two TB drugs - rifampicin and isoniazid - are defined as multidrug resistant (MDR). These strains are difficult and costly to treat, and require extensive regimens (Pratt et al, 2005). Risk factors for MDR-TB are outlined in Box 3.
There are now strains of TB that are not only MDR but also resistant to second line injectable and oral drugs (WHO, 2008c), and are described as being virtually untreatable. These strains are known as extensively drug resistant, or XDR-TB.
In the UK, 6.8% of cases are estimated to be resistant to any first line drug, and 1.1% as MDR-TB (HPA, 2009a). There have been a few cases of XDR-TB (Grant et al, 2008).
Little data is available from randomised controlled trials to guide treatment of drug resistant TB. Management of MDR-TB and XDR-TB is difficult and extremely expensive, and patients are increasingly managed in specialist centres (Grant et al, 2008). The All-Party Parliamentary Group on Global TB advocates managing those with MDR-TB in designated centres (BTS et al, 2009).

Conclusion

TB remains a major public health problem around the world, and is of increasing concern in the UK with the emergence of drug resistant TB and problems of HIV co-infection. The UK national strategies to control TB need to be fully implemented to achieve effective control. l

• Part 2 of this unit, to be published next week, examines the diagnosis and treatment of TB, in the UK and internationally

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