Pathophysiology

Dear Mrs. MRSA,

I have tested positive for a MRSA culture of my nose.  Does this mean I am sick?  I feel fine but from what I understand MRSA infection can be pretty bad.  Should I be worried?

Sincerely,

Nosy in Nebraska

Dear Nosy,

You can become colonized with s. aureus by coming in contact with another person who has the infection, or with their things.  Once colonized a break if there is a break in your bodies defenses, be it a break in skin though a cut, surgery, insertion of in-dwelling catheter or ventilator a more serious infection may result. 

Different strains of s. aureus can cause different problems.  For example some forms are good at hiding from the immune system, and others are very good at holding on to tissue or prosthetic devices.  After one has been colonized the bacteria can lay dormant, however if the genes are turned on s. aureus can cause septic shock, scalded skin syndrome, or other diseases by producing toxins and activating the immune system.  However, please note that the different strains of s. aureus do not behave the same.  Some may be more virulent (greater ability to cause infection) while others may be better suited to invade the body and stay there. 

MRSA Culture

Image Source https://www.flickr.com/photos/mediman30/9477953611/

As I mentioned above it really depends on the strain of MRSA one has what the progression of the disease will be.  However, if the s. aureus is resistant to common antibiotics and causes surgical-site infection, pneumonia, or blood stream infection the risk of death is much higher.  It is not well understood if this is because the strain of MRSA is more virulent, or if the patients who become sick were in poor health to begin with. 

One study showed that individuals who were previously colonized with MRSA (such as yourself) actually had better outcomes from blood infections than individuals who become infected without previously being colonized.

Simply being colonized with MRSA doesn't mean you will become sick.  However, if your skin becomes broken like in surgery your medical team will need to take extra care to make sure you do not develop a blood infection.  

Best of luck to you, Nosy!

Next week we will hear from another reader who has tested positive for MRSA.  

References  

Gordon RJ, Lowy FD.  Pathogenesis of Methicillin-Resistant Staphylococcus aureus Infection. Cli Infect Dis. (2008) 46(Supplement 5):S350-S359.doi:10.1086/533591