Workload and clinical significance of the isolation of zygomycetes in a tertiary general hospital

Several reports of increases in invasive zygomycosis (IZ) at individual institutions across the USA and Europe have contributed to a generalized concept that IZ is an increasing problem and the overestimation of the clinical significance of the isolation of zygomycetes in microbiology departments. We assessed the workload and clinical significance of zygomycetes isolates recovered from clinical samples in our institution over a 19-year period (1988-2006). We retrospectively reviewed the charts of those patients from who isolates of zygomycetes were obtained and calculated the workload of its isolation, the incidence of IZ during this period and the positive predictive value (PPV) of a positive culture. Zygomycetes were recovered from 210 samples (176 patients), i.e., 0.086/1,000 clinical samples processed and 6.3/1,000 samples submitted for fungal isolation. Zygomycetes represented 0.6% of the total fungi recovered. The mean incidence of the disease was 1.2 cases/100,000 admissions (range 0-20). Only 16 of the samples which grew zygomycetes (7.6%) were from infected patients. The workload generated by zygomycetes in our institution and the PPV for IZ of their isolation in our laboratory were very low and the disease was not found to have significantly increased in recent years in our institution. Data from specific institutions cannot be generalized.