Factors influencing time to sputum conversion among patients with smear-positive pulmonary tuberculosis

Time to sputum conversion in patients with pulmonary tuberculosis: A score to estimate the infectious period

Introduction

Patients with pulmonary tuberculosis (PTB) disease and positive sputum cultures are the main source of infection. Culture conversion time is inconsistent and defining the length of respiratory isolation is challenging. The objective of this study is to develop a score to predict the length of isolation period.

Methods

A retrospective study was carried out to evaluated risk factors associated with persistent positive sputum cultures after 4 weeks of treatment in 229 patients with PTB. A multivariable logistic regression model was used to determinate predictors for positive culture and a scoring system was created based on the coefficients of the final model.

Results

Sputum culture was persistently positive in 40.6%. Fever at consultation (1.87, 95% CI:1.02-3.41), smoking (2.44, 95% CI:1.36-4.37), >2 affected lung lobes (1.95, 95% CI:1.08-3.54), and neutrophil-to-lymphocyte ratio > 3.5 (2.22, 95% CI:1.24-3.99), were significantly associated with delayed culture conversion. Therefore, we assembled a severity score that achieved an area under the curve of 0.71 (95% CI:0.64-0.78).

Conclusions

In patients with smear positive PTB, a score with clinical, radiological and analytical parameters can be used as a supplemental tool to assist clinical decisions in isolation period.

Rapid DNA extraction for specific detection and quantitation of Mycobacterium tuberculosis DNA in sputum specimens using Taqman assays

Rapid tuberculosis (TB) detection is critical for disease control, and further quantitation of Mycobacterium tuberculosis (Mtb) in sputum is valuable for epidemiological and clinical studies. We evaluated a simple, robust and cost-efficient in-house DNA extraction and downstream Taqman approach for detection and quantitation of Mtb genomes from sputum of newly-diagnosed TB patients and non-TB controls. DNA was extracted using guanidine isothiocyanate and silica-based spin columns in less than 2 h, stored frozen, and Taqman assays were used to detect Mtb with IS6110 and quantify it targeting RD1 and IS1081. The Taqmans had a sensitivity >95% in 108 culture-confirmed TB patients and specificity of 100% in 43 non-TB controls. Genome counts were correlated with the Mycobacterial Growth Indicator Tubes' (MGIT) time-to-detection values (1/TTD × 1000; rho = 0.66; p < 0.001) in 91 TB patients (33 excluded with MGIT contamination). This linear relationship was nearly identical between mycobacteria isolated from sputum and H37Rv Mtb grown in-vitro to its log phase. TB treatment between 3 and 7 days was associated with lower 1/TTD × 1000 values but not with genome counts. Together, our protocol provides rapid, specific, inexpensive and quantitative detection of Mtb DNA in fresh or stored sputa making it a robust tool for prompt TB diagnosis, and with potential use for clinical and epidemiologic studies.

Old and new selective pressures on Mycobacterium tuberculosis

Tuberculosis (TB) has been affecting humans for millennia. There is increasing indication that human-adapted Mycobacterium tuberculosis complex (MTBC) has been co-evolving with different human populations. Some of the most important drivers of MTBC evolution have been the host immune response and human demography. These old selective forces have shaped many of the features of human TB we see today. Two new selective pressures have emerged only a few decades ago, namely HIV co-infection and the use of anti-TB drugs. Here we discuss how the emergence of HIV/TB and drug resistance could impact the long-term balance between MTBC and its human host, and how these changes might influence the future evolutionary trajectory of MTBC.

Geographic differences in time to culture conversion in liquid media: Tuberculosis Trials Consortium study 28. Culture conversion is delayed in Africa

Background

Tuberculosis Trials Consortium Study 28, was a double blind, randomized, placebo-controlled, phase 2 clinical trial examining smear positive pulmonary Mycobacterium tuberculosis. Over the course of intensive phase therapy, patients from African sites had substantially delayed and lower rates of culture conversion to negative in liquid media compared to non-African patients. We explored potential explanations of this finding.

Methods

In TBTC Study 28, protocol-correct patients (n = 328) provided spot sputum specimens for M. tuberculosis culture in liquid media, at baseline and weeks 2, 4, 6 and 8 of study therapy. We compared sputum culture conversion for African and non-African patients stratified by four baseline measures of disease severity: AFB smear quantification, extent of disease on chest radiograph, cavity size and the number of days to detection of M. tuberculosis in liquid media using the Kaplan-Meier product-limit method. We evaluated specimen processing and culture procedures used at 29 study laboratories serving 27 sites.

Results

African TB patients had more extensive disease at enrollment than non-African patients. However, African patients with the least disease by the 4 measures of disease severity had conversion rates on liquid media that were substantially lower than conversion rates in non-African patients with the greatest extent of disease. HIV infection, smoking and diabetes did not explain delayed conversion in Africa. Some inter-site variation in laboratory processing and culture procedures within accepted practice for clinical diagnostic laboratories was found.

Conclusions

Compared with patients from non-African sites, African patients being treated for TB had delayed sputum culture conversion and lower sputum conversion rates in liquid media that were not explained by baseline severity of disease, HIV status, age, smoking, diabetes or race. Further investigation is warranted into whether modest variation in laboratory processes substantially influences the efficacy outcomes of phase 2 TB treatment trials or if other factors (e.g., nutrition, host response) are involved.

Trial Registration

ClinicalTrials.gov NCT00144417

Factors influencing sputum smear conversion at one and two months of tuberculosis treatment

BACKGROUND

In the era of Direct Observation Treatment (DOT) for tuberculosis, clinicians need to focus on high-risk groups. We present sputum conversion rate at one and two months following DOT and its predictors in Oman.

STUDY DESIGN

Hospital-based clinical intervention type of case series.

METHODS

Chest physicians in a referral hospital examined sputum-positive cases of tuberculosis between 2001 and 2006. Patients with HIV infection and treated in the past were excluded. History of smoking, diabetes and duration of symptoms were noted. Sputum was tested for bacillus density. Blood was tested for platelet count and blood sugar levels. One and two months following treatment, the sputum was retested to determine sputum conversion. Regression analysis was done to identify the predictor of late conversion.

RESULTS

Of the 112 sputum-positive TB cases, 39 (34.8%) and 49 (43.7%) cases were sputum negative one and two months respectively after DOT. Lower platelet count was significantly associated with early sputum conversion. (Diff of mean = 38.3 cells x 9/L (95% CI 36.9 - 39.7). On univariate analysis, duration of symptoms, history of diabetes, smoking and ESR were not associated with the early sputum conversion. Knowledge of platelet count seems to assist the clinician to predict the early sputum conversion following DOT for pulmonary TB.

CONCLUSIONS

Sputum conversion rate among tuberculosis patients treated with DOT for one and two months in Oman was 34.8% and 78.6% respectively. Platelet count could assist in predicting early sputum conversion.

Tuberculosis and HIV infection. How to safely treat both disorders concurrently

Progress has been made in screening, early recognition, prevention, and treatment of TB, but its coexistence with HIV infection continues to present a challenge. Healthcare professionals should be familiar with guidelines for treating HIV-infected patients with TB while concurrently administering highly active antiretroviral therapy. Primary care physicians are encouraged to consult specialists who are familiar with treatment of patients with such coexisting disease. Whenever feasible, directly observed therapy should be instituted in all cases of TB to promote compliance and reduce the incidence of drug resistance and treatment failure.