Zoonotic Staphylococcus pseudintermedius sinonasal infections: risk factors and resistance patterns.

Background: Staphylococcus pseudintermedius is a Gram-positive bacteria that colonizes the skin and orifices of healthy canines and felines. It has recently been identified as a cause of sinonasal infections in humans.

Methods: This study was a retrospective review of chronic rhinosinusitis (CRS) patients with S pseudintermedius-positive sinonasal cultures and comparison to a prospectively collected control sample of patients who underwent culture for acute exacerbation of CRS.

Results: Thirty-three patients with CRS had nasal cultures positive for S pseudintermedius. Of the positive cultures, 82% demonstrated resistance to penicillin, 58% to clindamycin, 45% to trimethoprim-sulfamethoxazole, 33% to doxycycline, and 27% to oxacillin. Ninety-seven percent of patients with S pseudintermedius were dog owners. There was no significant difference in age, gender, recent endoscopic sinus surgery, or immunosuppression or deficiency between S pseudintermedius patients and patients undergoing culture for acute exacerbation of CRS, but S pseudintermedius infection was associated with dog ownership (p < 0.01). S pseudintermedius infection was not associated with behaviors such as a dog sleeping in the bedroom, routinely licking humans, or being diagnosed with a soft tissue infection.

Conclusion: Although a rare cause of infection in humans, S pseudintermedius should be considered in sinonasal infections refractory to standard medical management, especially if the patient has regular contact with dogs. S pseudintermedius is not readily identified with routine laboratory diagnostic testing and often demonstrates multidrug resistance, making it a pathogen that is commonly misdiagnosed and difficult to treat.