DR. CORDOVER: How can an emergency physician tell what the prevalence of methicillin-resistant Staph aureus is in his or her community?

DR. FOX: This is really a tough question. You might be inclined to reach in your pocket and look at the hospital antibiogram and try to extrapolate from the hospital-associated antibiogram as to what percentage of resistant Staphylococcus you have in the hospital compared to the community. But I believe that would be a fallacious assumption. There may be a general correlation with the hospital antibiogram, but the actual frequency in the community is really unknown.

There are very few surveys of communities for actually knowing the exact prevalence of communityassociated MRSA in a community. I mentioned the 1% rate in two large epidemiological studies that were performed but these were national based studies that represented a large cross section across the United States. The Center for Disease Control has been very slow to fund any type of research on the percentage of resistant Staphylococcus. There are some centers that know the prevalence in the community. If you are lucky enough to have that information available from your state health department I think that can be used to gauge your responses to your prescribing of anti-infective therapy.

I know that in the state of Wisconsin we do not know what the percent of MRSA is in our various communities, and unfortunately we just have to make some educated guesses. But the antibiogram itself that the hospital puts out every year is really only a very crude litmus test as to the prevalence of MRSA and I would not use that to guide my decision-making in the emergency department.

* * * * * * * * * * * *

DR. CORDOVER: From a practical point of view, are there risk factors or patient characteristics that could lead us to suspect CA-MRSA?

DR. FOX: This is an important issue because the risk factors for community-resistant Staph are going to help determine what kind of treatment options and approaches we’re going to take for the patient presenting to the emergency department or the urgent care settings. There are some profiles of patients that are at higher risk to have their skin colonized with community-associated resistant Staphylococcus. The following table summarizes this list for you; but, basically, if individuals live in crowded living circumstances, they’re at much higher risk for the acquisition of the community-associated resistant Staph.

So, some examples would include prisoners, military recruits, people in homeless shelters, individuals that live in crowded living circumstances within their home, and other types of circumstances where

Table 2. Risk factors associated with CA-MRSA infections

The following risk factors should increase suspicion for CA-MRSA in patients presenting with compatible signs and symptoms.

• History of MRSA infection or colonization in patient or close contact
• High prevalence of CA-MRSA in local community or patient population
• Recurrent skin disease
• Crowded living conditions (e.g. homeless shelters, military barracks)
• History of incarceration
• Participation in contact sports
• Skin or soft tissue infection with poor response to ß-lactam antibiotics
• Recent and/or frequent antibiotic use
• Injection drug use
• Member of Native American, Pacific Island, Alaskan Native populations
• Child under 2 years of age
• Male with history of having sex with men
• Shaving of body hair

There may be increased skin-to-skin contact such as athletic and sports teams. So any time there’s a circumstance where there’s the potential for close skin-to-skin or specifically fomite contact from sharing towels or linen or bedding we may have a higher frequency of community-associated MRSA. There have also been recent reports about homosexual populations having a higher frequency of community-associated MRSA.

* * * * * * * * * * * *

DR. CORDOVER: Increasingly the ED is treating skin abscesses that prove to be MRSA. Are skin abscesses more common in one or the other type of MRSA?

DR. FOX: This is another very good question. Since the community-associated strain possesses the PVL toxin about 95% of the time, the community-associated strain is much more likely to cause an abscess or abscess-based presentation in the skin. The traditional hospital-associated strains of MRSA can cause skin infections, but more frequently, we are seeing these in bloodstream or healthcare associated types of pneumonia compared to the community-associated strains.