Risk of infection with Mycobacterium tuberculosis in Malawi: national tuberculin survey 1994.

OBJECTIVE

To estimate the annual risk of tuberculosis infection among schoolchildren in Malawi.

METHODS

A school survey was conducted in twelve randomly selected districts in Malawi. Children in standard 1-4 and aged 6-11 years were eligible. Tuberculin skin testing was performed according to World Health Organization/International Union Against Tuberculosis and Lung Disease guidelines.

RESULTS

Of the 17123 eligible children, 80% were tested. Of those tested 79% were read. The prevalence of infection according to various criteria was 9-12% in children without bacille Calmette-Guerin (BCG) scar. The prevalence of reactions of 10 mm or more was lower in girls than in boys, increased with age, and was higher in those with than in those without BCG scar. The annual risk of infection was estimated to be within the range 0.6-1.4%.

CONCLUSION

Annual risk of infection in Malawi was in the order of 1%. This study is expected to provide valuable baseline information for an assessment of the impact of human immunodeficiency virus (HIV) on tuberculosis transmission in Malawi.