Quantitative Culture of Intravenous Catheters and Other Intravascular Inserts

Abstract

Quantitative cultures were done on 149 intravenous catheters and 40 additional intravascular inserts. Intradermal and intravascular segments of the insert were cultured separately. The inserts were immersed in broth and flushed. The number of colonyforming units (cfu) per insert was estimated by surface culture of serial dilution of the broth. Nonquantitative culture of undiluted broth was also done. Since all inserts associated with bacteremia had at least 103 cfu, inserts with >10³ cfu were considered infected. Staphylococcus epidermidis was more likely than more virulent organisms to colonize an insert without causing bacteremia. The inserts in one bacteremic patient were infected from a distant bloodstream focus; however, in the majority of patients, quantitative intradermal cultures suggested that the insertion site was the portal of entry. In bacteremic patients, either a positive quantitative or a nonquantitative culture identified an infected insert. However, only 33% of positive nonquantitative insert cultures from nonbacteremic patients were confirmed by quantitative insert culture.