One aspect of MRSA that is often not fully understood by the public is the concept of colonization vs. infection. Staphylococcus aureus is a bacteria that lives normally on human skin surfaces – in fact 40% of us have the little guys all over us right now as we sit here in front of our computers. MRSA, which is simply an antibiotic resistant strain of Staphylococcus aureus, can also live on our skin for long periods or even permanently without us ever knowing it. This is called colonization, and depending on the population group/risk profile most studies show that 5-10% of us are carrying MRSA around with us wherever we go. As far as sites of colonization this bacteria can live on virtually any skin surface, but they really love the warmest, dampest, darkest areas they can find including the nose, throat, armpits, and various sites “south of the border”. It is widely accepted in the medical community that the nose represents the primary reservoir of S. aureus/MRSA colonization in humans, with the throat emerging as another important area and all other sites considered secondary.
When a hospital discloses MRSA rates, or the media reports on MRSA incidence, they are almost always talking about infection rate as opposed to colonization rate. Active infection occurs when a bacterial strain undergoes uncontrolled growth. When the body attempts to mount a defense against this overgrowth you begin to see the typical, well known symptoms of infection including redness, pain, fever, etc. Infection can be localized to a specific area such as a wound, cut, or burn. More concerning, is when an infection spreads as a result of bacteria entering the blood supply and continuing to grow while circulating throughout the body. This is known medically as “bacteremia”, and is the most serious and deadly form of infection.
Some doctors and scientists think of colonization and infection not as distinct conditions, but as two points on a sort of continuum. While people colonized with MRSA regularly live happily unaware for many years, studies have proven that they are far more likely to develop an MRSA infection at some point than those not carrying the bug. Furthermore, asymptomatic (ie. non-infected) MRSA carriers can easily pass this bacteria on to others through direct contact or even just by living in the same environment. This is especially scary because while your immune system may do just fine dealing with 1,000,000 MRSA bacteria per square inch in your nose, your 80-year old grandmother, 6-month old infant, or cancer-fighting spouse may not be so lucky. This is exactly the reason why initiatives are popping up all over aiming to have all patients screened for MRSA prior to admittance into hospitals. There are simply too many immunocompromised patients, too much movement, and too great a risk within those walls to allow free passage of bacteria living silently on unaware carriers.
So next time you read a news story about MRSA, take a second to determine whether the issue being reported is one of colonization or infection. After that, think about how one is associated with the other and where the most logical point is to attack the problem. I think you’ll find yourself ending up at the old “treatment vs. prevention” argument, and we all remember what our mothers used to say about an ounce of prevention and a pound of cure…