My father had knee replacement surgery and somehow was infected with E. coli in the wound. How could this happen, and what is the recommended treatment for such an infection?

L.T.

Escherichia coli (E. coli) is a bacterium that causes several types of infections. Although E. coli is frequently mentioned in news reports of food poisoning outbreaks, it is actually far more commonly the cause of urinary tract infections. E. coli is found in almost everyone's colon (part of the large intestine), and when certain strains contaminate the urinary tract, infections can develop. Less common strains cause the outbreaks of food poisoning. While E. coli generally does not infect other sites in the body, it can cause wound infections after surgery. The most common cause of post-operative wound infections is Staphylococcus aureus, or staph, but virtually any organism can cause infection in an open wound.

I am more concerned about possible infection of your father's artificial knee than I am about the organism responsible. Once an infection begins in any prosthetic device (artificial body part), it is extremely difficult to eradicate. A common manifestation of such infections in the knee is a chronic wound that does not heal and drains pus. The pus will contain an organism (E. coli would be unusual, but not impossible) and the infection will be described as a "wound infection." A typical wound infection is treated by opening the wound, cleaning it up, and sometimes administering antibiotics -- but this course of action will not cure an infection of a prosthetic knee.

To cure a prosthetic joint infection, typically the entire prosthesis is removed, a temporary device impregnated with antibiotics is left in place for six weeks, and the patient is given intravenous antibiotics. Then, if the infection does not recur after antibiotics are discontinued, a new prosthesis is put in place. If less stringent measures are undertaken with a prosthetic joint infection, the infection will continue to smolder, leading to damage to surrounding bone. Not only will subsequent surgery to treat the problem become more difficult, the infection also could spread elsewhere in the body. The only way to absolutely rule out a prosthetic knee infection is to insert a needle into the area and withdraw fluid for culture. If there is any question about whether your father's knee is infected, this should be done.