Update on invasive aspergillosis: clinical and diagnostic aspects

Abstract

Apergillus is a ubiquitious mould that can cause a wide variety of clinical syndromes ranging from mere colonisation to fulminant invasive disease. Invasive aspergillosis (IA) is the most severe presentation of aspergillosis. The lung is usually the portal of entry, from which the pathogen may disseminate to almost any organ, often the brain and skin. The diagnosis remains a significant challenge. It is usually based on a combination of compatible clinical findings in a patient with risk-factors and isolation of the microorganism, radiological data, serological detection of antibodies or antigens, or histopathological evidence of invasion. Chest radiographic findings in patients with pulmonary Aspergillus may initially be normal in up to 10% of cases. Computed tomography scanning is probably the most useful imaging technique for the diagnosis of IA, since it may reveal lung lesions up to 5 days earlier than would radiograph techniques simply. Currently available laboratory diagnostic methods include several techniques: histopathological evidence of invasion; isolation of the microorganism and direct microscopy from clinical samples and non-invasive procedures (serological detection of antigens or nucleic material of Aspergillus; detection of antibodies). The histological diagnosis of IA requires the presence of invasion by fungus of the Aspergillus species. The truth is that, if no other variables are considered, the positive predictive value is very low, and most of the isolates of A. fumigatus do not represent proven or probable infection. Several molecules could be used as markers of infection, but two of them are of special interest: Aspergillus galactomannan (GM) and (1 fi 3)-b-glucan (BG). GM has a high specificity (above 85%) and a reported sensitivity that varies widely (between 30% and 100%). BG, a main cell wall polysaccharide component of Aspergillus, can be colourimetrically detected and is useful in diagnosis, with a sensitivity ranging from 50% to 87.5%. A specific Aspergillus PCR assay has also been used in the diagnosis of IA and has shown very good results, with a sensitivity and specificity of 100% and 89%, respectively.