MRSA- germs

Question

About 2.5 years ago I had an empyema of the knee joint because of MRSA after an injection and had then be operated 9 times on the knee and femur. It has been treated in the beginning with Linezolid (without success), then with Vancomycin. Discharge of the hospital after 3 months.
After a rehabilitation and longlasting physiotherapy and hard training I am able to walk again and to bend the knee to 110 degrees. Sportive activities like before the infection (jogging etc.) is not possible anymore. My question is, if there is the possiblity that remaining MRSA-germs could have encapsulated in the joint or the thighs, which could be probably getting active again at a knee-prosthesis operation, which is probably necessary in the next years? Is it realistic at all that after the time-interval of 2.5 years bacteria could still be encapsuled in the leg?

Answer

Dear questioner,
From your description I can assume, that you have had a complicated infection of the joint with S. aureus with remaining restriction of the movement of the knee joint.
An MRSA is a varaint of S. aureus which is resistant against many conventional antibiotics. Therefore you received the reserve-antibiotics Linezolid and Vancomycin, to which an MRSA is always almost sensitive. In spite of a sensitivity against those substances under test conditions in the laboratory, a therapy against MRSA and the healing process of the infection can be of long duration, especially as in your case with an infection of the bone.
S. aureus owns so many virulent factors, which can damage the cells of the body markedly. An infection with S. aureus is therefore causing often marked symptoms like signs of inflammation, fever and pain. A stay of S. aureus over a timeinterval of more than 2 years without any symptoms is very unlikely.

Overall, S. aureus is a frequent colonizing germ of the skin and mucosa (e.g. nasal vestibule) of healthy people but also a frequent cause of infection. S. aureus is able to cause different infections, among those (post-operative) wound-infections, infections of the bones as the so-called osteomyelitis or infections of joints and joint-protheses.
In your case there was a purulent infection of the joint (joint empyema) at the beginning. There are mainly 2 possible ways, how the germ could have reached the joint: either directly via a procedure from the outside, as an injection into the joint or a punction e.g. with a contaminated syringe with S. aureus or on the blood way (so-called septic arthritis). Hereby S. aureus bacteria are distributed from the entrance (e.g. a little abscessus) via the blood stream into the body, whereby spreadings at different sites e.g. the joints can emerge. In case your infection took place without a preceeding procedure, one has to assume a distribution via the blood stream. The causes of this could be differing and are not judgable without furhter information on details.

In case of long-lasting infections or because of permanent antibiotic therapy, S. aureus can build up so-called "Small colony varaints (SCVs)". These varaints of the germ grow slowly, and because of this the signs of infection are often less severe but in general nevertheless present. SCVs are therefore not easy to treat, and are able to cause more chronic infections and are at the same time harder to diagnose as the germs can often not be verified in the laboratory. In spite of that the SVCs cause as already mentioned an inflammation of the joint and therefore symptoms, so that in your case, even if SVCs would have been there, it can be mostly excluded that bacteria still remained.
Conclusion:
The presence of S. aureus in the joint after more than 2 years after the operation without any symptoms is very unlikely if not totally can be ruled out. The risk (which is also seldom but in general present) that it could come to a contamination of the prothesis of the joint in the frame of an implantation and as a consequence to a new infection of the joint, has to be judged to be higher. In this respect it would be important to clarify at least in the forefield of a planned operation if you still have a colonization with MRSA (e.g. nasal vestibule / skin) which could make a perioperative antibiotic prophylaxis during the procedure necessary. The risk of an MRSA infection has to be minimized as far as possible because of the limited antibiotic choice with this germ, because foreign bodies (e.g. implants) represent a preferred target for the formation of so-called biofilms by S. aureus.

Dr. Michael Hogart

06.09.2010