Background: In 2007, a field observation from India reported 11% misclassification among 'new' patients registered under the revised national tuberculosis (TB) control programme. Ten years down the line, it is important to know what proportion of newly registered patients has a past history of TB treatment for at least one month (henceforth called 'misclassification'). Methods: A study was conducted among new smear-positive pulmonary TB patients registered between March 2016 and February 2017 in 18 randomly selected districts to determine the effectiveness of an active case-finding strategy in marginalised and vulnerable populations. We included all patients detected through active case-finding. An equal number of randomly selected patients registered through passive case-finding from marginalised and vulnerable populations in the same districts were included. Before enrolment, we enquired about any history of previous TB treatment through interviews. Results: Of 629 patients, we interviewed 521, of whom, 11% (n=56) had past history of TB treatment (public or private) for at least a month: 13% (34/268) among the active case-finding group and 9% (22/253) among the passive case-finding group (p=0.18). No factors were found to be significantly associated with misclassification. Conclusion: Around one in every ten patients registered as 'new' had previous history of TB treatment. Corrective measures need to be implemented, followed by monitoring of any change in the proportion of 'previously treated' patients among all registered patients treated under the programme at national level.
Keywords: New TB; Previously treated TB; Recurrent TB; Tuberculosis/classification; Vulnerable populations.