Study design, participants and settings
The study site, design and participants have been reported previously [3]. Patients aged ≥18 years presenting with respiratory symptoms and attending participating TB clinics for the evaluation of possible TB were recruited to the study after providing written informed consent. At presentation, patients’ responses to a questionnaire were documented and two samples of sputum were submitted to the National TB Programme for routine Ziehl–Neelsen smear followed by culture and DST.
Laboratory methods
Detection of Mycobacterium tuberculosis (MTB)
Sputum samples were decontaminated according to the NaOH-NALC method [4]. Following this, an aliquot was used for microscopic examination of auramine-stained sputum smears and the remainder underwent parallel TB culture on Löwenstein–Jensen medium and in MODS liquid medium.
DST for rifampicin and isoniazid
Direct DST was performed with the MODS assay [5, 6]. Indirect DST was performed using the proportion method [7] for isolates from the Löwenstein–Jensen culture (by an external laboratory) and with the automated MBBacT system [8] for isolates from the automated mycobacterial culture.
Field methods
Clinical, epidemiological and socioeconomic data were collected using a standardized nurse-administered questionnaire. Data recorded included (1) the presence and duration of symptoms; cough, expectoration, fever, breathlessness, haemoptysis, weight loss, night sweats and chest pain; (2) risk factor exposures for TB or DR-TB, HIV infection, prior TB treatment, known TB or MDR-TB contact, healthcare or prison service worker, recent hospitalization or prison incarceration, drug and alcohol use, or BCG vaccination; and (3) indicators of household wealth related to income, education, overcrowding and sanitation contributing to the “Necesidades Basicas Insatisfechas”, a locally validated poverty score described and used by the Economic Commission for Latin America and the Caribbean [9].
Definitions
DR-TB was defined as strains of MTB resistant to rifampicin and/or isoniazid. Isoniazid mono-resistance was defined as resistance to isoniazid by any method without accompanying rifampicin resistance, rifampicin mono-resistance was defined as resistance to rifampicin by any method without accompanying isoniazid resistance, and multidrug resistance was defined as resistance to both rifampicin and isoniazid by any method [1]. The remaining strains were defined as drug susceptible.
MDR-TB risk factors included previous TB treatment, contact with a known MDR-TB patient, malabsorption, exposure to environments with high rates of MDR-TB (healthcare workers, prison workers and residents, previous hospitalisation) and HIV infection [10, 11].
Statistical analysis
Data were analysed using Stata 11 (College Station, TX: StataCorp LP 2010). The principal outcomes of interest were the proportion of DR-TB diagnosed among the population of non-selected subjects and the proportion of DR-TB diagnosed in subgroups of selected subjects with and without MDR-TB risk factors. Subgroups considered were subjects with previous TB, contact with MDR-TB, health workers, prison workers or residents, and HIV infection (MDR-TB risk factors [10]), by all subjects with any MDR-TB risk factor, and by smear positive subjects only. Analyses were also performed with and without inclusion of sputum smear results to reflect the recommendation that rapid testing should be used as the initial diagnostic test in adults with risk factors for MDR-TB in place of an initial sputum smear microscopy [1, 12]. The inclusion of the smear microscopy result evaluated the sensitivity of using DST as a follow-on test after initial smear microscopy.
The following calculations were undertaken for each subgroup in which subjects would be selected for DST: (1) number of DSTs that would be performed, (2) number and proportion of DR-TB patients diagnosed, and (3) number and proportion of DR-TB patients that would be missed.
The number of subjects in each MDR-TB risk factor subgroup were calculated to demonstrate the reduction in burden of DSTs required should testing be restricted to these subgroups.
Ethics review
Study protocol and consent forms were approved by the institutional review boards of Universidad Peruana Cayetano Heredia, Asociación Benéfica PRISMA, Dirección de Salud–III Lima Norte and IV Lima Este, Johns Hopkins Bloomberg School of Public Health, and Imperial College London.