Diagnóstico laboratorial das micobacterias isoladas na urina: comparação entre métodos convencionais e a reação da polimerase em cadeia (PCR)

Abstract

Tuberculosis is an ancient disease, responsible for thousands of deaths over the centuries, around the world, especially amongst less privileged populations and one which has recently spread due to Acquired Immune Deficiency Syndrome and the appearance of strains of Mycobacterium which are resistant to multiple drugs. Tuberculosis is caused by the genus Mycobacterium which contains 71 species, of which M. tuberculosis is the main cause of the disease. Mycobacterium. is transmitted through respiratory aerosols, initially settling in the lung, then spreading to any other organ. Amongst the other organs most affected, the most common is the kidney. The bacillus reach the kidneys via hematological route, settling in both organs at first, the lesions occurring on glomerules, which spontaneously heal in one of the kidneys. The laboratory diagnosis of tuberculosis is stil under improviment. Thus, we have: bacilloscopy, which is widely used, although the number of cases false negatives is high, as, in order for a positive Identification, there must be 5 to 10 thousand bacillus/friL of sample. Culture is the most sensitive microbiological method with the disadvantage of a delay in obtaining results, which varies from 21 to 60 days. Other means are used for diagnosis of tuberculosis, including Polymerase Chain Reaction (PCR). PCR is a highly efficient method for diagnosis of tuberculosis, as, by means from a single fragment of micobacterial DNA, it is possible to amplify thousands of copies of Deoxyribonucleic Acid (DNA). Thus, PCR was used on 886 urine samples in 528 “pools” from 176 patients. These PCR were performed using specifíc “primers” for either Mycobacterium genus and for the M. tuberculosis complex; in all negative cases, nested-PCR was performed. The results obtained were compared with conventional methods: bacilloscopy and culture. Comparing the methods, it was obtained the following results: sensitivity of 84.00% and specificity of 94.0% of PCR compared with bacilloscopy; sensitivity of 90.9% and specificity of 87.9%, of PCR compared with culture; sensitivity of 84.40% and specificity of 98.0% of the PCR compared with bacilloscopy and/or culture. A prevalence of: PCR 17.0%; bacilloscopy of 14.2% and to the culture 11.8% for Micobacterium sp. A prevalence of M. tuberculosis complex of 1.7% in 176 patients and a prevalence of 90.0% of atypical micobacteria in genito-urinary. Thus, it may be concluded that PCR is an excellent method for diagnosis of micobacteria of ginuto-urinary treat, being to diagnose positive cases more efficiently than bacilloscopy and culture.