[Evaluation of the galactomannan assay for the diagnosis of invasive aspergillosis in an animal model].

Objective: To assess the value of Aspergillus galactomannan (GM) double-direct sandwich enzyme-linked immunosorbent assay (ELISA) in the diagnosis of invasive pulmonary aspergillosis (IPA).

Methods: Ninety adult SD rats were randomly divided into 5 groups, including 4 groups of pulmonary infection by Aspergillus fumigatus (A. fumigatus), Candida albicans, mucor, and Streptococcus pneumoniae, respectively, and a colonization group by A. fumigatus in the pharynx oralis (n = 18 each). For the infection models, suspensions of pathogenic bacteria and fungi were instilled into the lungs of the rats by tracheal intubation. For the colonization model, the suspension of A. fumigatus was applied to the nasal cavity and pharynx oralis of the rats. The animals were sacrificed on days 3, 7, and 12 after inoculation, and blood samples were obtained by cardiac puncture and used for GM detection. The lung tissues were prepared for routine pathology examination, and hexamethylene tetramine silver staining was used to detect the fungi. A double-direct sandwich ELISA was employed to detect GM optical density index in the serum samples.

Results: The lung tissues of rats infected with A. fumigatus, Candida albicans, mucor and Streptococcus pneumoniae all showed remarkable inflammatory reactions, and hyphae were observed in rats with fungal infection (including A. fumigatus and mucor), and spores in rats infected with Candida albicans. The lung tissues of the A. fumigatus colonization rats showed no inflammatory reactions. The serum GM optical density index of the groups infected with A. fumigatus, Candida albicans, mucor and Streptococcus pneumoniae, and the A. fumigatus colonization group were 1.69 +/- 0.29, 0.89 +/- 0.46, 0.87 +/- 0.39, 0.77 +/- 0.34 and 0.90 +/- 0.49, respectively. The serum GM optical density index of the IPA group was higher than those of the other 4 groups (P < 0.05). If the cutoff ODI was 1.5, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for diagnosis of IPA in the rats were 78.6%, 87.5%, 57.9% and 94.9%, respectively. The sensitivity for A. fumigatus infection on days 3, 7, and 12 was 60.0%, 80% and 100%, and the specificity was 95.5%, 81.0% and 85.7%, respectively.

Conclusion: GM detection could distinguish Aspergillus infection from Candida albicans, mucor, Streptococcus pneumoniae infection and Aspergillus colonization. The sensitivity of the test for the diagnosis of IPA tended to be higher with longer duration of infection. A cutoff ODI of 1.5 showed the best sensitivity and specificity for IPA in this rat model.