Sept. 29, 2011 -- Dental students in a Seattle study had very high rates of colonization with MRSA, the drug-resistant strain of staph, raising new questions about the prevalence of the bacteria outside of hospitals in community health care settings.
People who are colonized with MRSA carry the bacteria in their nose or on their skin, but they may or may not have signs or symptoms of infection. They can spread MRSA to others, however.
Nasal swabs from one in five University of Washington (UAW) Dental School students tested showed evidence of methicillin-resistant Staphylococcus aureus, and four of seven dental clinics at the school also tested positive for the bacteria in samples taken from dental chairs and floors.
The rate of MRSA colonization was significantly higher than that reported in the general population and in other non-hospital medical settings, but an official with the CDC says the public should not be overly alarmed by the findings.
Arjun Srinivasan, MD, says the high MRSA rate suggests a specific transmission at the UAW facility and is probably not indicative of rates in dental offices in general.
Srinivasan is assistant director for the CDC’s Healthcare-Associated Infection Prevention Program.
“This study is one of the first to look at MRSA in the dental setting, but it was a small study with just 61 dental students in one facility,” Srinivasan tells WebMD. “We don’t believe this study necessarily represents a systematic problem in dental clinics across the country.”
Community MRSA Rates Rising
MRSA is usually highly resistant to the antibiotics most often used to treat staph infections, and it is a significant cause of illness and death among hospitalized patients with compromised immune systems.
Infections that happen outside the hospital setting -- known as community-acquired MRSA -- tend to occur in otherwise healthy people and they typically show up as skin infections.
Recent surveys suggest that hospital-acquired MRSA has declined within the past few years, while rates of community-acquired MRSA appear to be increasing, according to the CDC.
Outbreaks of community-acquired MRSA have been reported in locker rooms, gymnasiums, prisons, military barracks, and other facilities where skin-to-skin contact is common and people share close quarters.
It is not clear how many people carry MRSA, but studies suggest that health care workers have slightly higher rates of colonization than the general population, University of Washington professor of environmental and occupational health Marilyn C. Roberts, PhD, tells WebMD.
MRSA Common in Buffalo Dental Study
In a study reported earlier this year, Roberts and colleagues found a high rate of MRSA colonization among a group of Seattle-area firefighters.
In their latest investigation conducted at the UAW dental school, the researchers took nasal swabs from 61 dental students and swabbed 95 surfaces considered potential reservoirs for MRSA.
Thirteen (21%) of the students and eight (8.4%) surfaces from four of the seven clinics harbored MRSA.
The study was published online today and will appear in the October issue of the American Journal of Infection Control.
An unrelated study of dental school students and instructors in Buffalo, N.Y., showed an even higher rate of colonization, with 31% of the 84 people showing evidence of MRSA.
That study was presented at a 2009 meeting of dental researchers held in Miami.
Roberts says the Buffalo findings show that the high MRSA colonization rate reported in her study is not limited to her institution.
Roberts and the CDC’s Srinivasan do agree that more study is needed to develop a better understanding of the rate of MRSA colonization in non-hospital health care settings.
The extent to which this colonization impacts MRSA infection rates is also not clear, he adds.
“We know a great deal about the infection control challenges related to MRSA in acute care hospital settings, but we know a lot less about this issue in non-acute care settings such as dental and dialysis centers and ambulatory surgical centers,” Srinivasan says.
Srinivasan says it does not appear that these settings represent a major source of community-acquired MRSA transmission.