[Genetic diagnosis of mycobacterium infections by polymerase chain reaction (PCR)]

Diagnosis is often difficult for mycobacteria because of the limitations of both direct microscopy and cell culture. Polymerase chain reaction (PCR), widely developed in microbiology, could provide major progress in the diagnosis of tuberculosis and atypical mycrobacterial diseases. Sensitivity rarely exceeds 80% and can be lower than 60% compared with traditional culture techniques. The specificity of tuberculosis PCR is rarely better than 97% so that the positive predictive value varies from 5 to 75% depending on the incidence of tuberculosis in the tested population (from 0.2 to 10%). The sensitivity of PCR compared with traditional culture varies from 2 to 90% depending on the laboratory. The proportion of false negative usually varies from 3 to 20%. Reliability should be improved with standardized simplified techniques, but quality control remains essential to validate the method in each laboratory. Current management strategies cannot be developed or changed solely on the grounds of PCR results.