Comparison between Smear-Positive and Smear-Negative Pulmonary Tuberculosis

Abstract

Background: Tuberculosis is a communicable disease that is a major cause of ill health, one of the top 10 causes of death worldwide. The diagnosis of tuberculosis can be strongly inferred by finding acid-fast bacilli (AFB) by microscopic examination. Some patients have clinical and radiological features of pulmonary tuberculosis but AFB negative.

Objectives:  To determine the difference between smear positive and smear negative pulmonary tuberculosis regarding clinical features, risk factors, and radiological features.

Patients and Methods A cross sectional study was conducted on 120 patients from different regions in Baghdad at randomly distributed health care centers, from 1^st April  2019 to 1^st February 2020, through a questionnaire including demographic data, risk factors, symptoms and chest X-rays findings. The patients were divided into two groups; smear-positive (whose sputum tests reveal positive acid fast bacilli in at least one out of the three successive tests) and smear-negative (who are diagnosed to have pulmonary TB despite that their three successive sputum tests give negative results to acid fast bacilli test). The criteria used to diagnose smear negative relied on the WHO guidelines. P values < 0.05 were considered statistically significant.

Results: Out of 120 patients, 58% were smear-positive, and 42% were smear negative, the highest age group in smear positive was in those ≥ 64years, while the highest age group in smear negative between 18-40years. Positive smear was significantly statistically positively associated with hemoptysis and consolidation and negatively associated with the use of steroid and cavitation.

Conclusions: Smear positive and smear negative pulmonary tuberculosis have similarities in clinical and radiological features, but hemoptysis and consolidation were higher in positive than in negative smears, while the use of steroids and cavitation were higher in negative than positive smears.