Predicting results of mycobacterial culture on sputum smear reversion after anti-tuberculous treatment: a case control study

Chin-Chung Shu,Chih-Hsin Lee,Li-Na Lee,Chong-Jen Yu,Jann-Yuan Wang,Jann-Tay Wang

doi:10.1186/1471-2334-10-48

Abstract

BackgroundLittle is currently known regarding sputum smear reversion (acid-fast smear becomes positive again after negative conversion) during anti-tuberculous treatment. This study aimed to evaluate its occurrence in patients with pulmonary tuberculosis (TB) and identify factors predicting results of mycobacterial culture for smear-reversion of sputum samples.MethodsThe retrospective review was performed in a tertiary referral center and a local teaching hospital in Taiwan. From 2000 to 2007, patients with smear-positive culture-confirmed pulmonary TB experiencing smear reversion after 14 days of anti-tuberculous treatment were identified.ResultsThe 739 patients with smear-positive pulmonary TB had 74 (10%) episodes of sputum smear reversion that grew Mycobacterium tuberculosis in 22 (30%) (Mtb group). The remaining 52 episodes of culture-negative sputum samples were classified as the non-Mtb group. The anti-tuberculous regimen was modified after confirming smear reversion in 15 (20%). Fourteen episodes in the Mtb group and 15 in the non-Mtb group occurred during hospitalization. All were admitted to the negative-pressure rooms at the time of smear reversion. Statistical analysis showed that any TB drug resistance, smear reversion within the first two months of treatment or before culture conversion, and the absence of radiographic improvement before smear reversion were associated with the Mtb group. None of the smear reversion was due to viable M. tuberculosis if none of the four factors were present.ConclusionsSputum smear reversion develops in 10% of patients with smear-positive pulmonary TB, with 30% due to viable M. tuberculosis bacilli. Isolation and regimen modification may not be necessary for all drug-susceptible patients who already have radiographic improvement and develop smear reversion after two months of treatment or after sputum culture conversion.

Highlights

Little is currently known regarding sputum smear reversion during anti-tuberculous treatment
Of the 46 episodes of smear reversion that developed after November 2006, nine (20%) were due to viable M. tuberculosis bacilli
The results showed that factors independently predicting the results of mycobacterial culture on smear reversion were any TB drug resistance (OR: 10.33; 95% C.I.:1.47-72.60), sputum smear reversion within 2 months after anti-tuberculous treatment (OR: 16.31; 95% C.I.: 2.02-131.64), smear reversion before sputum culture conversion (OR: 29.55; 95% C.I.: 4.07-214.72), and no radiographic improvement before smear reversion (OR: 23.57; 95% C.I.: 2.49-223.38) (Table 3)

Summary

Introduction

Little is currently known regarding sputum smear reversion (acid-fast smear becomes positive again after negative conversion) during anti-tuberculous treatment. To prevent further dissemination of Mycobacterium tuberculosis from TB patients, adequate anti-tuberculous treatment with the implementation of the Directly Observed Therapy (DOT) is important [5]. In some TB patients, follow-up sputum smears occasionally reveal AFB after negative conversion (smear reversion). The anti-tuberculous regimen is modified under the impression of treatment failure, drug resistance, or poor adherence. Only those with viable M. tuberculosis bacilli should receive proper isolation and further work-up. The commercialized nucleic acid amplification tests, despite good sensitivity and specificity, are expensive and do not discriminate between viable and dead bacilli [7]

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