Determining Factors Affecting Time to Sputum Smear Conversion in Pulmonary Tuberculosis Patients Using Cox Semi-Parametric Method


1 Master Student of Biostatistics, Biostatistics and Epidemiology Department, School of Health, Mashhad University of Medical Sciences, Mashhad, Iran

2 Professor of Biostatistics, School of Health, Management and Social Determinant of Health Research Center, Mashhad University of Medical Science, Mashhad, Iran

3 Assistant-Professor of Social-Medical Sciences, Biostatistics and Epidemiology Department, School of Health, Mashhad University of Medical Science, Mashhad, Iran

4 Vice Chancellor for Health, Mashhad University of Medical Sciences, Mashhad, Iran

5 Professor of Biostatistics, Health Sciences Research Center & Biostatistics and Epidemiology Department, School of Health, Kerman University of Medical Science, Kerman, Iran


Background & Aims: Tuberculosis is one of the most important diseases of century that involves all the human organs including lungs. Due to the yearly occurrence of 9 millions new cases and 1.5 millions deaths in the world, tuberculosis is in the center of attention. The aim of this study was to indentify factors affecting the time required for sputum smear conversion in patients.
Methods: This historical cohort study was performed on tuberculosis patients with pulmonary involvement and positive smear referred to Health Centers of Mashhad University of Medical Sciences from September 2012 to July 2014. The demographic characteristic of patients and features of disease were used as variables. Log Rank test, Kaplan-Meier method and Cox regression were used to analyze data (α<0.05).
Results: Out of 1141 patients, 54.8% were female and 45.2% were male. The medium time to sputum smear conversion was 2 months. At the end of the second and third months of treatment, respectively 78% and 89% of patients had negative smear. Based on Cox regression, gender and bacillus level at the beginning of treatment significantly affected the time to sputum smear conversion.
Conclusion: Special attention must be paid to the patient education and to the male patients and those with high level of bacillus at diagnosis time.


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