Towards a molecular diagnosis of invasive aspergillosis? A review of the literature

Certain diagnosis of invasive aspergillosis (LA) is difficult. This disease , which requires an early diagnosis and treatment for the best outcome and prognosis, seems to constitute a good diagnostic applica tion of PCR. Moreo ver, this new molecular biology technique has already been applied to the d iagnosis of parasitic and fungal infections (toxoplasmosis, Pneumocystis ca rinii pneumonia). The objectives of this review are to assess the different techniques of PCR developed for the detection of Aspergillus spp. DNA during the invasive pr ocess and to discuss the results of the methods used in clinical applicatio ns. The different PCR techniques which have been described can be split into tw o types of procedures. The first one uses specific primers of A. fumigatus or Aspergillus spp., and hybridization confirms the specificity; in the sec ond. the fungal DNA is detected by universal fungal primers. Then the genus or species of Aspergillus is identified by species-specific hybridization. The sensitivity and specificity of these different techniques are generall y correct. Three authors have evaluated their PCR techniques in samples fro m an experimental mouse model of IA. The correlation rate between culture a nd/or histology of pulmonary samples and PCR was between 83 % and 93 %. The seven PCR techniques detailed here are most often carried out on biolog ical samples collected from clinical studies. Among these, four have been a dapted to detect Aspergillus DNA in bronchoscopic fluids (bronchoalveolar l avage), two are used on serum and the last one is used on blood (allowing t he detection of Aspergillus DNA and also the DNA from other fungi). Among the bronchoscopic samples, many faire positive results have been obse rved, probably due to the presence of conidies in the patients' airways. Th e PCR performed on serum or blood allows better specificity (with a lower s ensitivity on serum). This review allows us to conclude that today none of these PCR techniques c an easily be performed in all microbiological laboratories for the diagnosi s of IA. The choice of sample is a deciding Factor and only PCR performed o n blood samples seems to combine satisfactory sensitivity and specificity. Finally, simplification and standardisation of the methods will be necessar y to develop Aspergillus -PCR to meet the urgent demand of physicians.