Canine Staphylococcus pseudintermedius sinonasal infection in human hosts.

Background: Staphylococcus pseudintermedius is a gram-positive bacterium commonly found as part of the normal skin and nasal flora of healthy dogs. It may act as an opportunistic pathogen in dogs, but has also been shown to colonize the nasal mucosa of humans. We report 4 cases of chronic rhinosinusitis (CRS) refractory to aggressive medical management with cultures that grew S. pseudintermedius, with clinical improvement only after initiating culture-directed therapy.

Methods: Retrospective review of 4 patients with CRS treated at a tertiary academic medical center with sinonasal cultures growing S. pseudintermedius.

Results: All 4 patients are dog owners and had clinical diagnoses of CRS. Three of the 4 patients had a diagnosis related to immune dysfunction (sarcoidosis, Crohn's disease, history of lymphoma). After undergoing endoscopic sinus surgery, each patient was treated with aggressive medical therapy but continued to have purulent nasal discharge. Sinonasal cultures repeatedly grew S. pseudintermedius in all cases, with 3 patients' dogs also having had concurrent S. pseudintermedius wound infections of the ear and leg with similar antibiotic susceptibilities. Treatment with culture-directed therapy improved the infections in all cases.

Conclusion: Opportunistic pathogens have a propensity to exacerbate infection in CRS patients with immune dysfunction. We report the first case series of sinonasal S. pseudintermedius infection in humans. Though a rare cause of disease, pathogens such as S. pseudintermedius from nonhuman hosts should be considered in the management of CRS patients refractory to medical therapy.