Can sputum induction aid in identifying micro-organisms that cause respiratory tract infections other than tuberculosis? A tertiary care hospital experience

<b>Background:</b> At our institution, when patients suspected to have tuberculosis and are unable to provide sputum or brochoscopy is delayed logistically, nebulized hypertonic saline sputum induction (SI) is performed to obtain micro-biological samples. The aim of this study is to report pathogens other than tuberculous identified in induced sputum in patients presenting with respiratory illness. <b>Methods:</b> A retrospective study was performed to investigate the outcomes in patients with suspected tuberculosis who had SI between March 2012 and October 2019. <b>Results:</b> 252 patients (mean age 54 ±SD 20 years; Male 53%) had sputum induction for suspected tuberculosis. Tuberculosis was excluded by negative sputum smear, culture and PCR in 162 patients (64.3%). The most common final diagnosis was pneumonia 61 (37.4%). Other diagnoses included bronchiectasis 8 (4.9%), asthma 6 (3.7%) and pulmonary nodules 5 (3.1%). The commonest non-tuberculous pathogens identified from induced sputum included Yeasts 44 (27%), staph.aureus 7 (4.3%), pseudomonas 3 (1.8%). Importantly, no organism was identified in 97 specimens (59.5%). <b>Conclusion:</b> In the present series of patients with suspected tuberculosis other microorganisms were identified in 66 patients (26.2%) by SI. Thus, SI can exclude tuberculosis and provide alternative microbiological diagnoses in a significant minority of patients. However, no microorganisms were identified in 97 patients (38.5%). The management of this subgroup is challenging, particularly if the risk of bronchoscopy is high. Further investigation and perhaps empirical therapy requires careful consideration.