Culture of intravenous catheter tips has been a routine practice for the past 10 years. Based on the findings of Maki et al. (Maki, D.G., C.E. Weiss, and H.W. Sarafin. 1977. A Semiquantitative Culture Method for Identifying Intravenous Catheter-Related Infection. N Engl J Med 296:1305- 1309), a quantitative technique based on rolling the tip on a blood agar plate and counting the resulting number of colonies has been a standard practice in most laboratories. The validity and value of these cultures has come into increasing debate, but little well-documented data has been published to clarify this issue. As part of a larger line-maintenance protocol in the Critical Care Medicine Department, our study will use these patients to look at colony counts and their predictive value in determining line sepsis from short- term central lines. Approximately 200 patients have been enrolled in this study. Organisms from patients who have positive blood cultures and concomitantly positive catheter tip cultures will be examined by molecular typing methods to determine if the catheter tip isolates are identical to the blood culture isolates, thereby supporting catheter-related bacteremia. Patient accrual has been completed and molecular analysis of the strains of bacteria (strain typing) isolated from these patients is still in progress. The rate of infection following placement of these lines was low, so the number of episodes to assess is limited. Preliminary review of the data, however, suggests that, although patients with positive blood cultures commonly have> 15 colonies on the rolled catheter culture, there were instances when the colony counts were < 15. In addition, there were cases where the organism cultured from the catheter tip was not the same as that cultured from the blood, and instances where catheter tip cultures yielded> 15 colonies but were not associated with positive blood cultures. Typing of strains and analysis of the data is ongoing.
