Microscopic observation drug susceptibility assay for tuberculosis screening prior to isoniazid preventive therapy in HIV-infected persons

Background

Isoniazid preventive therapy reduces the risk of progression of latent Mycobacterium tuberculosis infection to active tuberculosis disease in patients with HIV. Prior to the administration of isoniazid preventive therapy, active tuberculosis must be excluded. Current screening strategies involving multiple tests and visits result in patient attrition and missed diagnoses due to the poor sensitivity of clinical history and exam, chest radiography, and sputum smear. Rapid, sensitive detection of tuberculosis and multidrug-resistant tuberculosis has previously been demonstrated with the microscopic-observation drug-susceptibility (MODS) assay, a low-cost culture technique.

Methods

HIV-positive candidates for isoniazid preventive therapy were recruited from three hospitals in Lima, Peru. All participants underwent simultaneous screening for TB by MODS culture of two sputum specimens and by the current Peruvian screening strategy involving clinical history and exam, chest radiography, sputum smear, and Lowenstein-Jensen culture. Time to result, completion of algorithm, and costs of the strategies were also assessed.

Results

MODS culture detected more cases of tuberculosis than Lowenstein-Jensen culture and currently used screening strategies. Time to culture-positivity or negativity was less for MODS than for Lowenstein-Jensen. There were ultimately fewer indeterminate culture results for MODS than for Lowenstein-Jensen, enabling the confident exclusion of TB in more people.

Conclusion

A TB screening strategy involving two MODS cultures of sputum specimens offers more sensitive and rapid detection of TB than do currently used screening strategies. TB is confidently excluded in more people using MODS cultures, enabling them to proceed to isoniazid preventive therapy.