CONTRIBUTION OF THE POLYMERASE CHAIN-REACTION TO THE DIAGNOSIS OF TUBERCULOUS INFECTIONS IN CHILDREN

The purpose of the study was to evaluate the contribution of polymeras e chain reaction (PCR) to the diagnosis of tuberculous infection in ch ildren. Two different PCR techniques were compared to the standard bac teriological methods for the detection of Mycobacterium tuberculosis i n 157 specimens obtained from the respiratory system of 51 children. P atients were classified in three groups: 12 patients with active disea se (57 specimens), 12 patients with silent tuberculous infection (23 s pecimens) and 27 patients without tuberculosis (77 specimens). One PCR method (PCR/Ag85) used amplification of a fragment of the genes codin g for the mycobacterial antigen 85 followed by hybridization of a prob e specific for M. tuberculosis on the Southern blot of amplified DNA. The other PCR technique was a nested PCR (NPCR) using double amplifica tion of a fragment of the insertion element IS6110 only present in the M. tuberculosis genome. The sensitivities of the different techniques , compared to the clinical diagnosis, were 7.0%; for acid fast stainin g, 22.8% for culture, 24.6% for PCR/Ag85 and 44.9% for NPCR in active disease, 4.3% for culture, 8.7% for PCR/Ag85 and 28.6% for NPCR in sil ent tuberculous infection. The specificities were 100% for culture, 94 .8% for PCR/Ag85 and 87.9% for NPCR. Among the 12 children clinically considered as having active tuberculosis, 1 had smear positive samples , 4 had at least one positive culture, 7 at least one positive PCR/Ag8 5 and 9 at least one NPCR positive sample. Among the 12 children havin g silent tuberculous infection, none had positive smears, 1 had one po sitive culture, 2 had at least one positive PCR/Ag85 and 5 at least on e NPCR positive sample. Conclusion Our study suggests that both PCR te chniques, and especially NPCR, are able to detect M. tuberculosis DNA in specimens containing few micro-organisms. PCR methods are more sens itive than culture and the results are available more quickly. Testing multiple samples from the same individual increased the sensitivity. In view of occasional false-positive results, cultures remain the gold standard to establish definitive diagnosis of primary tuberculous inf ection in children.