Galactomannan antigenemia detection for diagnosis of invasiveaspergillosis, Part II

Diagnosis of invasive aspergillosis by galactomannan antigenemia detection using an enzyme immunoassay

Invasive aspergillosis is a serious and often fatal infection in patients who are neutropenic or have undergone solid organ or stem cell transplantation. Delayed diagnosis and therapy may lead to poor outcomes. Diagnosis may be facilitated by a test for galactomannan antigen detection using an enzyme immunoassay. Other rapid methods for diagnosis include (1-->3)-beta-D: -glucan determination and polymerase chain reaction. The sensitivity and specificity of galactomannan antigenemia testing in serum and bronchoalveolar lavage specimens are high in patients with hematological malignancy, neutropenia, and receipt of stem-cell transplants. False positivity can be seen with concomitant administration of some antibiotics and infection by fungi other than Aspergillus.

Preemptive antifungal therapy: still a way to go

PURPOSE OF REVIEW

Early treatment of invasive mold infections improves the outcome. Therapy is often delayed, however, because available diagnostic tools such as culture, microscopy and conventional radiology lack sensitivity; consequently, empirical initiation of antifungal therapy has been advocated, particularly for patients with prolonged unexplained neutropenic fever.

RECENT FINDINGS

Much recent progress has been made in the development and evaluation of nonculture-based assays, including the detection of the fungal antigens galactomannan and beta-D-glucan and the detection of fungal DNA by polymerase chain reaction techniques. These new tools should aid the rapid, early diagnosis of invasive fungal disease, especially when used as screening tools in conjunction with sensitive imaging techniques.

SUMMARY

The review will consider these recent developments with the purpose of introducing the concept of preemptive antifungal therapy.

Antigen detection, serology, and molecular diagnosis of invasive mycoses in the immunocompromised host

Understanding the uses and limitations of methods for rapid diagnosis of fungal disease is essential in order to diagnose and treat these infections early in their course. Antigen detection methods are useful for diagnosis of aspergillosis, cryptococcosis, histoplasmosis, blastomycosis, paracoccidioidomycosis, and penicilliosis marneffei. The accuracy of the beta-glucan assay for diagnosis of aspergillosis and candidiasis and its role in fungal diagnosis remains unclear, in part because the few published studies report widely varying specificity. Serologic tests for antibodies are also useful for diagnosis of histoplasmosis and coccidioidomycosis, but their sensitivity may be reduced by immunosuppression. While molecular diagnostic methods have been described and are available at some reference and university laboratories, their role in patient care remains uncertain, largely because of the lack of well-characterized assays and studies establishing their accuracy. Culture methods, although essential for establishing the diagnosis in some cases, have limitations for rapid diagnosis, namely insensitivity, need for invasive procedures, and delayed growth.