Contemporary Update on the Microbiology of Paranasal Sinusitis

Background: Sinusitis, whether acute or chronic, is likely due at least in part to disruptions in the microbiota of the paranasal sinuses. Sinus cultures are often employed to guide medical treatment. Objective: To quantify the contemporary microbiology of the paranasal sinuses and better understand the utility of paranasal sinus cultures. Methods: We identified patients from 2018 to 2019 with sinus cultures taken by an otolaryngologist in the outpatient setting in our healthcare system with a concurrent diagnosis of acute or chronic rhinosinusitis. These cultures were analyzed based on their culture type and result. The most commonly isolated bacteria were further analyzed by species; Staphylococcus resistance patterns were analyzed as well. Results: A total of 2302 culture samples were collected: 2012 (87%) bacterial, 287 (13%) fungal, and 3 (0.1%) mycobacterial cultures. The results of more than half (1142, 57%) of these bacterial cultures were positive for a named genus, while those of 592 (29%) were positive for normal sinus flora and 16 (0.8%) for normal oral flora, and those of 183 (9%) showed no growth. The results of another 79 (4%) bacterial cultures were positive for unnamed bacteria, which were not further classified (e.g., Gram-negative rods). Of the positive bacterial cultures with named genera, the most common genera identified was Staphylococcus (383, 34%). Of these, the most common species of Staphylococcus was S. aureus (311, 81%), 42 of which (14%) showed methicillin resistance (MRSA). Of the fungal cultures, 265 (92%) resulted in no growth, and all three mycobacterial cultures showed no growth. Conclusions: In contrast to fungal cultures, the majority (57%) of sinus bacterial cultures showed positive results, with the identification of a named genus, highlighting the potential utility of this assay in guiding medical therapy.