Clinical features of local inflammation suggest a catheter-related infection:
(1) swelling
(2) erythema
(3) lymphangitis
(4) increased warmth
(5) tenderness
(6) palpable venous thrombosis
(7) pus or discharge
Technique:
(1) Remove any dressing over the catheter.
(2) Remove any antimicrobial ointment or blood with an alcohol swab and clean the skin surface.
(3) Remove the catheter using sterile forceps.
(4) The distal 5 or 6 cm of the catheter is cut with sterile scissors and placed into a sterile tube.
(5) Longer catheters also have a 5-7 cm length of catheter taken extending proximally from the portion in the subcutaneous tissue. This is also placed into a sterile tube.
(6) In the laboratory a 100 mm 5% sheep blood agar plate is prepared.
(7) The catheter tip is rolled back and forth over the agar at least 4 times. If the catheter is bent then the tip is brought back and forth using sterile forceps.
(8) If a second piece was taken then this is cultured in the same manner.
(9) Each plate is incubated for 48 hours and the colonies counted.
Interpretation:
• minimum number of colonies on culture: 0
• maximum number of colonies: confluent growth
• The presence of >= 15 colonies indicates catheter-related infection. Most cases with clinical catheter-related infection showed confluent growth.
Additional criteria for the diagnosis of a catheter-related septicemia:
(1) The patient has clinical signs of septicemia.
(2) The same organism is isolated from both the semiquantitative culture and a peripheral blood culture.
(3) Other sources of infection are excluded.
Performance:
• The method was more specific than culturing the catheter tip in broth. Culturing the tip in broth can be positive in cases of bacteremia from an infectious focus remote from the catheter.
Limitations:
• The catheter has to be removed for the culture to be taken.
