Transmission of Mycobacterium tuberculosis to households of tuberculosis patients: a comprehensive contact tracing study

ABSTRACT

Tuberculosis [TB] continues to be a major health problem in developing countries. Contact investigation is the most appropriate strategy to interrupt transmission and subsequent development of TB. This cross-sectional study was conducted to assess the impact of contact screening on case-finding by using tuberculin skin test chest radiography. Contacts of smear-positive patients with pulmonary TB [index cases] were diagnosed and registered in our center during 2002 - 2004. Contacts, defined as household members living with index cases for >30 days, were screened by sputum examination, tuberculin skin test, and chest radiography. Sixty-eight patients with smear-positive pulmonary TB were considered as index cases. A total of 224 close contacts with index cases [an average of 3 contacts for each index case] were detected. Age among contacts ranged from 6 months to 74 years. Eighty-three percent of contacts were Iranians and 17% were Afghans. Abnormal radiographs were seen in 49.6% of contacts. Sixteen point five percent of contacts had a positive tuberculin skin test of >10 mm; 7.6% had a positive sputum smear. The mean - SD age of Iranian contacts [29.1 +/- 16.6 years] was significantly [P < 0.001] higher than that of Afghans [18.6 +/- 14.1 years]. Cavitary formation, nodular pattern, and infiltration were found to have a strong association with a positive sputum smear for acid fast bacilli [100%, 100%, and 87%, respectively]. The rate of TB in contacts was higher than other similar studies. Earlier detection and treatment of adults with TB could interrupt transmission and be a step towards eliminating childhood TB. Contact control and source-case investigations should be emphasized for TB control. Novel strategies are needed to maximize the number of contacts who are not only identified and evaluated, but also completely treated