TB in Leicester: out of control, or just one of those things?

Recent increases in tuberculosis in the UK reflect a global problem

Last year in England and Wales 235 schoolchildren aged 5-14 were notified with tuberculosis. Most will not have been infectious—for example, those with tuberculous lymphadenitis—but some of the 148 children with pulmonary tuberculosis will have been smear positive and potential sources of infection. For each of these children local tuberculosis services will have searched for linked cases by screening household members and other close contacts, including those at school.1

Evidence of transmission of infection from a child index case in a school to other children is not often found1—but outbreaks in schools do occur. Although adults, usually staff, are often the source of infection, schoolchildren have also been reported.2^–6 The essential element in these outbreaks is an infectious patient whose illness may have been undiagnosed for a long period. Local environmental circumstances and the opportunity to expose many people also contribute to the scale of an outbreak.

What therefore should we be asking about the recent outbreak of tuberculosis in Leicester7 that has made headline news? Is it a one off event due to unusual circumstances or a sign of a growing problem in a local community which may be common to other urban communities in the United Kingdom?

The Leicester outbreak is the largest reported in a UK school. Although measures have been taken to prevent further spread of infection at the school, the precise circumstances that resulted in the outbreak are not yet clear. Fortunately the strain of Mycobacterium tuberculosis appears to be susceptible to standard antituberculosis drugs, and treatment should be fully effective. Currently we know that over 62 people, mainly schoolchildren, have been found to have active tuberculosis, and a further 99 are strongly tuberculin sensitive on skin testing, suggesting recent or previous subclinical infection. Though the explosive nature of the outbreak suggests a common, highly infectious source case, the cases may not all be linked to the same source.

The investigation now underway is likely to reveal chains of transmission that link clusters of cases with strains of M tuberculosis present in the local community. Modern molecular methods of strain typing will enable recognition of truly related cases, including those in the wider community, whose links would otherwise have gone unrecognised, and distinguish unrelated cases. Thus it should be possible to understand better the circumstances associated with exposure and infection.

The incidence of tuberculosis in Leicester is high: 152 cases were reported in the 1998 national tuberculosis survey (52 per 100 000 population, compared with 10.9 in England and Wales), reflecting the high proportion of the local population originating in the Indian subcontinent, where tuberculosis rates are high.8 The overall rate in Leicester has changed little, however, in recent years. Cases in other Leicester schools have also recently been reported, but these are likely to be “expected” cases, and no connection has been found between these and the outbreak school.

The Leicester outbreak is not related to the two year lapse of the national schools' BCG immunisation programme, which is restarting this summer, as 80% of children at the school, including most of those with active disease, have been immunised. Many Leicester schoolchildren will have been vaccinated as neonates or infants in line with the policy of offering BCG to those at increased risk.1 However, BCG provides only partial protection against tuberculosis. 9 10 Although neonatal vaccination has been shown to be protective in children in Britain, 11 12 the level of protection from this early vaccination may have waned. The protection that BCG immunisation appears to have provided students at the school is being estimated.

This outbreak could have occurred anywhere, but potentially infectious cases are more likely to occur in areas where rates of tuberculosis are high. Most of the recent increase in the incidence of tuberculosis in England and Wales has occurred in London. In 1990 the 1603 cases notified in London accounted for just over 30% of cases in England and Wales: by 2000 these had risen to 2938 and 43% of cases. The incidence of tuberculosis in some London boroughs exceeds 50 per 100 000.11 Managing these cases effectively, and preventing further spread, presents a considerable task for inner city health authorities. The steep rise in tuberculosis in New York in the late 1980s and the associated increase in multidrug resistant disease has already provided a warning that tuberculosis remains a threat.13 The outbreak in Leicester adds a further warning about the importance of establishing and maintaining effective services for the diagnosis, treatment, and surveillance of tuberculosis. In particular, adequate numbers of specialist nurses are needed as they provide the backbone of local tuberculosis services. But it is not just a question of resources. Prompt diagnosis of cases depends on being alert to tuberculosis as a possibility, particularly in people from high risk groups. Awareness of tuberculosis is currently high because of the Leicester outbreak, but this needs to continue beyond the ripples of anxiety prompted by media reports of this outbreak.

Moreover, tuberculosis remains a global health problem. The breakdown in health services, the spread of HIV infection, and the emergence of multidrug resistant tuberculosis in many parts of the world are contributing to the worsening impact of the disease. Although this impinges on the UK—nearly 60% of new cases of tuberculosis in England and Wales in 1998 occurred in people born in high prevalence parts of the world8—it may all seem far away from a Leicester school where a local outbreak has been contained. It is crucial, however, that as well as maintaining its own effective tuberculosis services, the UK continues to work in partnership with countries where the disease is highly prevalent to help control the global problem of tuberculosis.