Rapid diagnosis of nocardiosis with an enzyme immunoassay

Diagnosis of nocardiosis is often delayed because of the frequently nonspecific nature of the illness and because of the long incubation period required to isolate the organism in the microbiology laboratory. Past experience with serological methods for diagnosing nocardiosis have met with little success, primarily because there was no suitable antigen. Using a previously identified Nocardia asteroides-specific protein, we developed an enzyme immunoassay for the rapid diagnosis of nocardiosis. We evaluated sera from 22 patients with nocardiosis, 83 hospitalized controls, and 21 patients with tuberculosis. Twenty (91%) of the sera from patients with nocardiosis had titers of antibody greater than or equal to 1:256, whereas all of the sera from controls and from patients with tuberculosis had titers less than 1:256. This assay represents a highly sensitive and specific serodiagnostic tool for evaluating patients with possible nocardiosis.