Diagnosis of the pulmonary tuberculosis by polymerase chain reaction: a comparative study between HIV - positive and - negative individuals

[Current characteristics of tuberculosis and human immunodeficiency virus co-infection in a cohort of hospitalized patients in Medellín, Colombia]

INTRODUCTION

Tuberculosis (TB) is an important cause of morbidity and mortality in HIV patients. It is unknown if the advent of molecular diagnostic methods and a greater availability of antiretroviral therapy (ART) in our country have changed some characteristics of the TB/HIV co-infection.

OBJECTIVE

To describe the epidemiology, clinical features, diagnosis, resistance patterns, tuberculosis drug effects and mortality in co-infected patients.

MATERIALS AND METHODS

Retrospective study based on the review of medical records of hospitalized co-infected adults in a university hospital in Medellín, Colombia.

RESULTS

A total of 178 patients was included in the study. TB and HIV diagnosis was simultaneous in 49.4%. In the moment of TB diagnosis, the median CD4 count was 61 cells/μL (27-145). Pulmonary tuberculosis (PTB) occurred in 28% of patients, extrapulmonary (EPTB) in 23%, and mixed TB in 48.9%. The main EPTB affectations were lymphatic (55.4%), gastrointestinal (35.9%), and of the central nervous system (18.7%). Ziehl-Neelsen stain was positive in 137 patients (77%), mycobacterium culture in 121 (68%), and TB-PCR, in 85 of those patients in whom the test was done. Rifampicin resistance was detected in six cases (4.9%). Transaminases (ALT) increased in half of the patients during TB treatment, but only 10% met liver-toxicity criteria. In-hospital mortality was 11.3%. The single risk factor associated with mortality was CD4 count <50/μL (RR=3.9; 95% CI: 1.36-11.37; p=0.01).

CONCLUSIONS

When it occurs as an opportunistic infection, TB usually leads to the diagnosis of advanced HIV disease. If used appropriately, TB diagnosis in these patients can be done by conventional methods. It is always necessary to monitor liver function during TB treatment and to rule out drug resistance.

Evaluation of four molecular methods for the diagnosis of tuberculosis in pulmonary and blood samples from immunocompromised patients

The present study analysed the concordance among four different molecular diagnostic methods for tuberculosis (TB) in pulmonary and blood samples from immunocompromised patients. A total of 165 blood and 194 sputum samples were collected from 181 human immunodeficiency virus (HIV)-infected patients with upper respiratory complaints, regardless of suspicious for TB. The samples were submitted for smear microscopy, culture and molecular tests: a laboratory-developed conventional polymerase chain reaction (PCR) and real-time quantitative PCR (qPCR) and the Gen-Probe and Detect-TB Ampligenix kits. The samples were handled blindly by all the technicians involved, from sample processing to results analysis. For sputum, the sensitivity and specificity were 100% and 96.7% for qPCR, 81.8% and 94.5% for Gen-Probe and 100% and 66.3% for Detect-TB, respectively. qPCR presented the best concordance with sputum culture [kappa (k) = 0.864)], followed by Gen-Probe (k = 0.682). For blood samples, qPCR showed 100% sensitivity and 92.3% specificity, with a substantial correlation with sputum culture (k = 0.754) and with the qPCR results obtained from sputum of the corresponding patient (k = 0.630). Conventional PCR demonstrated the worst results for sputa and blood, with a sensitivity of 100% vs. 88.9% and a specificity of 46.3% vs. 32%, respectively. Commercial or laboratory-developed molecular assays can overcome the difficulties in the diagnosis of TB in paucibacillary patients using conventional methods available in most laboratories.