Catheter-related infections and blood cultures

Catheter-related infections with both local inflammation and bacteremia or fungemia are common in hospitalized patients. The diagnosis of these infections is not, however, straightforward. Evidence of local inflammation is helpful, if present, but is not always found with site infections, and blood cultures are not positive. Systemic infection is associated with positive blood cultures, but the finding of a positive blood culture does not identify the catheter as the source. With central catheters, making a diagnosis without having to remove the catheter would be useful, because many of these patients could be treated with antibiotics without catheter removal. Multiple methods have been described for identification of these infections. Semiquantitative cultures of the catheter tip performed by rolling the catheter on the surface of an agar plate are the most popular. For central catheters, many advocate obtaining blood cultures through the catheter and comparing the results by quantitative methods with peripherally obtained blood cultures. No method has clearly demonstrated a clinical benefit in large numbers of patients. Because the most serious manifestation of catheter-related infection is bacteremia or fungemia, ordinary blood cultures are of the most practical importance in the identification of patients requiring therapy. Whether any of the additional studies described can be justified in everyday laboratory practice or simply represent considerable wasted effort is not known. Better methods for identifying infections and for managing such infections in patients with long-term indwelling central catheters are needed.