Additional risk of developing TB for household members with a TB case at home at intake: a 15-year study.

Tuberculosis Research Centre, Indian Council of Medical Research, Chennai, India.

International Journal of Tuberculosis and Lung Disease; 2007; 11; 282–288.

Objective: To assess the additional risk to household contacts from an infectious case of tuberculosis (TB) at home in a rural community in south India.

Methods : In all, 3506 contacts of smear-positive (S+C+) and 2910 contacts of smear-negative TB cases (S-C + ) and 246 845 persons with no TB case at home were followed for 15 years, with a repeat survey every 2.5 years consisting of radiographic and sputum examination, selective follow-up of high-risk individuals and passive surveillance. If a case developed during follow-up, all household members were subsequently considered as contacts. Cox's proportional hazards model (multivariate) was employed to compare incidences.

Results: The annual incidence of culture-positive TB was respectively 526 and 271 per 100 000 population for contacts of smear-positive and smear-negative patients, and 198/100 000 in non-contacts. The adjusted hazard rate was 3.4 for contacts of smear-positive patients (95% CI 3.0–3.9) and 1.7 for contacts of smear-negative patients (95% CI 1.4–2.0) as compared to non-contacts. Of 3942 incident cases, 337 (8.5%) came from households with a TB case.

Conclusion: Although family contacts had a significantly higher incidence, their contribution to total new caseload was meagre. Contact chemoprophylaxis as a public health measure would therefore have limited impact on community TB incidence.

Keywords: TB infectivity; risk to contacts; chemoprophylaxis

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