Risk of Staphylococcus aureus (S. aureus) and Methicillin-Resistant S. aureus (MRSA) Nasal Carriage among Dental Healthcare Providers (DHCP)

Background: S. aureus and MRSA are common causes of community and hospital acquired infections. Nosocomial spread of the organisms can be influenced by the extent of nasal carriage among healthcare providers (HCP). Studies suggest that hospital HCP have significantly higher MRSA nasal carriage compared to the general population (4.6% vs 0.8%, p<0.0001). Given the close proximity with which DHCP interact with patients, nasal carriage of S. aureus or MRSA among DHCP could represent a reservoir for spread in this setting. We sought to assess whether or not DHCP had the same risk for S. aureus or MRSA nasal carriage than the published rates for hospital HCP and the general population.

Methods: We prospectively determined nasal carriage rates of S. aureus and MRSA among 49 randomly selected DHCP from our College of Dental Medicine by performing two anterior nares swabs per provider. One swab was used to inoculate Mannitol Salt Agar and the other CHROMagar® MRSAII. Media were incubated and scored according to the manufacturers’ specifications. We then compared the rates of positivity for each organism to those published for hospital HCP (23.7% for S. aureus and 4.6% for MRSA)¹ and for the general population (31.6% for S. aureus and 0.8% for MRSA)² utilizing Fisher’s Exact Test.

Results: Twenty-two (44.9%) of the 49 DHCP tested positive for S. aureus nasal carriage and 3 (6.1%) of the 49 DHCP tested positive for MRSA nasal carriage. Compared to hospital HCP, the rate of S. aureus carriage was significantly higher (OR 2.6, p=0.0009) among DHCP; however, was no different for MRSA carriage (OR 1.3, p=0.9). Compared to the general population, DHCP had significantly higher rates of S. aureus and MRSA nasal carriage (OR 8.3, p<0.0001 and OR 1.9, p=0.04, respectively).

Conclusion: In our study, DHCP were significantly more likely to have S. aureus or MRSA nasal carriage than the general population, more likely to have S. aureus nasal carriage than hospital HCP and were just as likely to have MRSA nasal carriage as hospital HCP. DHCP should be considered an important reservoir of spread for S. aureus and MRSA within healthcare, comparable to that of providers in the hospital.
¹Lancet Infect Dis 2008;8:289-301. ²Ann Intern Med 2006;144:318-325.