Acquired Resistance to Isoniazid During Isoniazid Monotherapy in a Subject with Latent Infection Following Household Rifampicin-Resistant Tuberculosis Contact: A Case Report

Appropriate treatment is the key element in eliminating tuberculosis (TB), and requires prompt diagnosis. We presented a case of a household contact of rifampicin-resistant TB revealing reactive IFN-gamma release assay with unsuspicious clinical and radiologic examinations. She was diagnosed with latent tuberculosis infection (LTBI) and treated with isoniazid monotherapy. On the ninth month, she developed a progressive cough and was found to harbor active TB disease with added resistance to isoniazid. An individualized anti-TB regimen consisting of moxifloxacin, kanamycin, prothionamide, ethambutol, and pyrazinamide was prescribed for 20 months, leading to sputum culture conversion and improvement of the reported symptom. No recurrence was observed on one-year follow-up. Assuming high compliance to therapy, we propose that the patient may have been under-diagnosed and received sub-optimal treatment leading to acquired-drug resistance. Conventional diagnosis methods based on immunological assay and radiographical findings may be insufficient to distinguish the incipient and subclinical states of TB from LTBI.

Automated summary

This case report highlights the importance of appropriate treatment and prompt diagnosis in eliminating tuberculosis. The patient initially diagnosed with latent tuberculosis infection later developed active TB disease with drug resistance, but showed improvement and no recurrence after individualized anti-TB treatment for 20 months. The study suggests that traditional diagnostic methods may not be sufficient to differentiate different stages of TB or LTBI.