Beta-D-Glucan Test May Detect Fungal Meningitis

SAN DIEGO—Testing the CSF for beta-D-glucan may be an accurate method of detecting fungal meningitis, according to research reported at the 65th Annual Meeting of the American Academy of Neurology.

Beta-D-glucan testing may help in “the diagnosis and therapeutic monitoring of fungal meningitis, [and] sequential quantification could assist in the determination of therapy duration,” said Jennifer Lyons, MD, postdoctoral fellow at Johns Hopkins University in Baltimore.

Beta-D-glucan is a protein in the cell wall of many fungi, including Candida and Aspergillus, and in the organism implicated in a recent outbreak of fungal meningitis, Exserohilum rostratum. “CSF is an immune-privileged site, so you should have no beta-D-glucan in your CSF,” said Dr. Lyons.

Dr. Lyons and her colleagues used the Fungitell assay, a serum beta-D-glucan test manufactured by Beacon Diagnostic Laboratories (East Falmouth, Massachusetts), to check for beta-D-glucan in CSF samples from six patients who were sick after receiving injections suspected of being contaminated with organisms that cause fungal meningitis.

Four patients met the CDC’s definition of probable meningitis but had negative cultures. Polymerase-chain reaction (PCR) testing in three patients was negative. All four patients with probable meningitis had detectable beta-D-glucan in their CSF samples.

One patient was sampled before and after two weeks of voriconazole treatment. It corresponded with a decrease in the patient’s beta-D-glucan titer. Although they were sick, the two other patients did not meet the CDC’s criteria for probable meningitis. They had no detectable beta-D-glucan in their CSF.

CSF culture is the usual diagnostic test. A CSF PCR assay is sometimes used as well, but this test is “largely unvalidated,” noted Dr. Lyons. “It basically amplifies fungal elements, [but it has a] low sensitivity. You can have an infection and be completely missed by this assay,” she explained. The CDC has been using the PCR assay during the recent outbreak, but less than a third of the recent cases of fungal meningitis were positive by PCR, said Dr. Lyons.

“For every single [fungal meningitis] case we suspected, [the test] was positive. That said, it’s hard to hang your hat on this,” said Dr. Lyons. The sample size was small, and the finding is no more than an observation, she added. “The next step is to validate the assay by defining cutoff values and false positives.”

—M. Alexander Otto
IMNG Medical News