UCSF

Methicillin-resistant Staphylococcus aureus (MRSA) is a staphylococcal bacterium that is resistant to beta-lactam antibiotics. Today, MRSA accounts for 50-70% of the nosocomial S. aureus infections acquired in healthcare facilities. MRSA contaminated surfaces and MRSA colonized human carriers can act as reservoirs for transmission, and dental clinics may serve as a source of disease transmission in the community.

Objective: Survey an 18 chair university-based periodontal clinic for MRSA contamination among hard environmental surfaces, dental unit water lines (DUWLs), aerosols, and human carriers.

Methods: (1) Hard environmental surface contamination. 18 air-water syringes (AWS) from the assistant's rack were swabbed, incubated for 24 hours, and streaked onto a selective chromogenic medium that detects MRSA (CMRSAII). (2) DUWL contamination. The Millipore heterotrophic plate count sampler was used to sample water from the 18 DUWLs. Following a 48-hour incubation, grown colonies were inoculated on the CMRSAII plates. (3) Dental procedure aerosol contamination. The Millipore M Air T Tester was used to collect 1000L of aerosol during ultrasonic scaling procedures or surgical procedures using highspeed handpieces. After a 24-hour incubation, colonies morphologically consistent with S. aureus were picked, sub-cultured, and swabbed onto CMRSAII plates. (4) Human carriers. 30 healthy volunteers were recruited among the periodontal residents, staff, and faculty (IRB#12-08736). Specimens were obtained from the anterior nares, incubated overnight, then triple streaked onto CMRSAII plates.

Results: (1) The AWS swabs yielded no MRSA colonies at 24 or 48 hours. (2) No MRSA were detected in the DUWLs. (3) 21 aerosol samples were taken during periodontal procedures using ultrasonics or dental handpieces. No MRSA were detected. (4) 30 samples from the anterior nares were collected and no MRSA were detected. Four individuals had Methicillin-resistant coagulase-negative staphylococci.

Conclusion: This study did not detect MRSA in the university-based periodontal clinic on environmental surfaces, DUWLs, aerosols, or human carriers. The literature so far, in conjunction with the data from this study, collectively suggests that the occupational risk of MRSA infection in a dental setting is probably minimal.