Infection status of Mycobacterium tuberculosis among close contacts of students diagnosed with smear-positive pulmonary tuberculosis in Zhuji, Zhejiang, 2008-2013

Objective To understand the infection status of Mycobacterium tuberculosis among the close contacts of the students diagnosed with smear-positive pulmonary tuberculosis (TB) in Zhuji, Zhejiang province and provide the evidence for pulmonary TB control and prevention in schools. Methods PPD test was conducted among the close contacts of the students diagnosed with smear-positive pulmonary TB in Zhuji during 2008-2013. Stratified analysis was conducted to identify the related factors to strong positive rate of PPD test among close contacts of the students diagnosed with smear-positive pulmonary TB. Results Totally 1721 close contacts of 28 smear-positive students were surveyed, the strong positive rate of PPD test was 23.24% (400/1721). Meanwhile totally 1409 non-close contacts of smear-positive students were surveyed too, the strong positive rate of PPD test was 2.77% (39/1409). The difference between the two groups was statistical significant (χ2=269.33, P=0.000).The related factors to strong positive rate of the close contacts included the onset season, sputum bacteria content and diagnosis delay of the TB patients. The positive rate of PPD test among the close contacts was high when the onset of TB patients were in winter and spring, especially when the sputum bacteria content of the TB patient was high (χ2=10.12, P=0.00；χ2=5.35, P=0.02). The positive rate of PPD test among the close contacts was high when the sputum bacteria content of the TB patient was high, especially when the onset of the TB patient was in spring (χ2=14.42, P=0.00；χ2=11.25, P=0.00). Diagnosis delay of the TB patients had influence on strong positive rate of the close contacts when the sputum bacteria content of the TB patient was low. The influences of diagnosis delay of the TB patients in winter and spring on the strong positive rate of close contacts were different (χ2=4.60, P=0.03). There was no statistical significance in strong positive rate among the close contacts of TB patients whose onset were in different seasons when the sputum bacteria content of the TB patient was high. Conclusion The related factors to the strong positive rate of PPD test of the close contacts of smear-positive students included the onset seasons, sputum bacteria content and diagnosis delay of the TB patient, but the influences of onset season and sputum bacteria content were more obvious.