Tuberculosis in the young: focusing on those at risk

Tuberculosis (TB) is curable and preventable, yet causes more deaths worldwide than any other infectious disease -- three million yearly, with 450 000 involving children. Australia has one of the lowest rates of TB in the world, and multidrug-resistant TB has not emerged as a problem here.^1,2 None the less, people born overseas, Aboriginal people, those infected with HIV, the elderly (especially men over 65), and the homeless experience much higher than average rates of disease.

Children up to the age of 14 years account for only 3%-6% of all Australian notifications. Children are also much less likely to transmit infection than adults. However, they have a high risk of developing active disease -- 23%-43% for those infected in the first year of life, 8%-25% for those infected between one and 10 years of age, and 16% for those infected when aged 11-15 years.³ Thus, it is important to identify infected children for preventive therapy (i.e., usually isoniazid for six months) to prevent progression to disease. Children born overseas, child contacts of infectious (usually adult) patients and Aboriginal children have much higher than average rates of infection and disease and deserve specific TB control strategies.

The primary strategy for TB control is to stop transmission by timely diagnosis and curative treatment of infectious patients. The next priority, especially in children, is to identify by Mantoux testing those infected and to initiate preventive therapy where appropriate. Screening of at-risk groups and contact tracing of cases are important for both these strategies. It is also important that the skills and resources for diagnosing and curing TB are available to health care providers serving those at risk, such as general practitioners working in high risk migrant communities, Aboriginal medical services and regional chest clinics or public health units.

The overall age-specific rates in Australia in 1995 were highest in overseas-born children aged 0-4 years (approximately 44, compared with 1 per 100 000 in Australian-born children of the same age).⁴ By contrast, 5-14-year-olds, whether born in Australia or overseas, have the lowest specific rates of any age groups, a finding that is consistent worldwide. In this issue of the Journal, the Consensus Statement⁵ on strategies for TB control in children in Australia from two paediatric special interest groups recommends Mantoux screening of immigrant children from high prevalence countries. This recommendation is long overdue, but needs a workable strategy. Issuing a Tuberculosis Undertaking (as is done for any adult migrant considered to be at increased risk of TB) to all children under five years of age emigrating from countries of high TB prevalence (> 25 per 100,000) would obligate a parent or guardian to contact the Health Assessment Service of the Department of Immigration and Multicultural Affairs within a specific period for direction to the nearest centre for Mantoux testing. The Health Assessment Service is currently investigating the feasibility of such a proposal.

Findings from the Melbourne study by Johnson and colleagues⁶ on the prevalence of asymptomatic Mycobacterium tuberculosis infection in secondary school students add to earlier studies from Sydney,^7,8 the Northern Territory⁹ (NT) and South Australia¹⁰ (SA) in supporting targeted school screening. Clearly, there is no current evidence to support mass school screening, and efforts should be directed towards students from countries of high TB prevalence to identify those at risk of developing active, contagious TB in adulthood and to offer them preventive therapy.

TB is detected in around 1% of contacts of active cases. While contact tracing finds up to 10% of notified cases of TB overall, this percentage is much higher in children. In 0-14-year-olds, 65% of all cases¹¹ and 78% of intrathoracic cases¹² were identified by contact tracing. TB in a child which is not found by contact tracing usually signals recent transmission within the family, providing an opportunity to diagnose adult TB and stop further transmission. Alternatively, it may indicate inadequacies in current control methods, such as failure to trace contacts or to promote successful preventive therapy in identified infected children. The forthcoming National Health and Medical Research Council (NHMRC) publication Towards elimination of tuberculosis II emphasises the importance of contact tracing and provides detailed guidelines for contact screening.³

Limited national data are available on TB in Aboriginal children, but reports from Queensland, SA and the NT confirm they are at increased risk of infection and disease. In the NT from 1989 to 1997, Aboriginal children represented 25 of the 28 notified TB cases aged 0-14 years. Twelve of these 25 cases were nodal TB, consistent with the high rate of extrapulmonary disease seen in children; in contrast, only two cases of non-tuberculous (atypical mycobacteria) nodal disease were found. Suspected mycobacterial disease of lymph nodes always requires culture and susceptibility testing, and in Aboriginal as in migrant children should be considered as TB until proved otherwise. This is in contrast to the 1989 NHMRC statement "that in children born in Australia, mycobacterial disease of lymph nodes is almost invariably due to atypical mycobacterial disease".¹³ Strategies for TB control among Aboriginal children include diligent contact tracing, which may extend to community screening due to sociocultural interactions and overcrowded housing,³ and targeted school Mantoux testing, education and preventive therapy in regions of high TB incidence.⁹

The Consensus Statement lists BCG vaccination as an important control strategy, and recommends extending this beyond Aboriginal and Torres Strait Islander neonates in regions of high incidence, neonates born to parents with leprosy, and children under the age of five years living or travelling in countries of high TB prevalence for more than three months, as recommended by the NHMRC TB Working Party.³ While BCG vaccination protects against disseminated TB in the young, it has not played a large role in reducing transmission and controlling TB worldwide. Children born in Australia with one or both parents born overseas are at no higher risk of infection than those with Australian-born parents.^6,7,8,9,10 Present evidence therefore supports continuing BCG vaccination according to the three recommendations above. Comprehensive information about the actual TB cases notified in all Australian-born children would be useful to further evaluate this issue.

The recommendation that specialised State and Territory TB control programs be maintained in a climate of economic rationalism for a disease with low national rates and low rates in children⁵ is appropriate. However, an international focus is also required. To this end, it is encouraging that TB has been recognised as a priority issue by the Advisory Group on International Health of AusAID. With 75% of cases being in the migrant population, and Australia's location between two regions which the World Health Organization estimates account for two-thirds of the world's 8-9 million cases, we can not work alone towards eliminating TB. Australia needs to be a partner in the region as well as a contributor to global TB-control strategies.

Vicki L Krause
Director, Centre for Disease Control
Territory Health Services, Casuarina, NT

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