A myco-management problem: improving utilization of fungal and mycobacterial smear and culture

Fungal and mycobacterial smear and culture are often inappropriately ordered, straining clinical laboratory resources and risking patient harm from false-positive results. To identify opportunities for optimization, we assessed utilization and yield of fungal and mycobacterial smear and culture over five years at a large academic medical center in an area of low tuberculosis prevalence. Positive rates were generally lower for non-respiratory specimens compared to respiratory specimens, prompting us to focus on collection method (swab vs non-swab) and location (operating room [OR] vs non-OR) for non-respiratory specimens. For non-respiratory fungal smear and culture, swabs demonstrated poor recovery of mold in culture, and positive smear results from swabs rarely affected clinical management (6/3,611 cases [0.17%]). Positive rates were significantly lower among OR specimens. For mycobacterial smear and culture, positive rates were exceedingly low for non-respiratory specimens (smear: 70/23,661 [0.3%]; culture: 278/23,918 [1.2%]). Swabs were inferior for mycobacterial culture, and positive smear results from swabs rarely impacted clinical management (3/7,398 cases [0.04%]). Among patients with at least one non-respiratory mycobacterial smear or culture over a two-year period, the smear or culture was diagnostic in only 32/4,572 (0.70%), 31 (96.9%) of whom had risk factors for mycobacterial infection. The smear result changed clinical management in only 5/4,497 cases (0.11%). Our results reveal considerable overutilization of fungal and mycobacterial smear and culture for non-respiratory specimens and confirm the low yield of non-respiratory swabs for mold and mycobacterial detection. These data inform strategies to optimize fungal and mycobacterial diagnostic testing in clinical laboratories.

Fungal and mycobacterial infections are associated with specific risk factors. However, diagnostic studies for fungal and mycobacterial infections, including fungal and mycobacterial smear and culture, are often inappropriately ordered in clinical scenarios where the probability of infection is low. Due to the manual nature of these tests, high volumes of unnecessary testing strain limited clinical laboratory resources. In addition, patients can be harmed by false-positive results. In this study, we analyzed the results of fungal and mycobacterial smear and culture performed over five years at a large academic medical center in a location with low tuberculosis prevalence to identify strategies to reduce unnecessary testing. Implementation of these strategies could allow clinical laboratories to optimize fungal and mycobacterial diagnostic testing and more efficiently use limited clinical laboratory resources without compromising patient care.