Infection Control & Hospital Epidemiology
1173
Fig. 2. Contact tracing of potential source patient in the outbreak investigation of nosocomial acquisition of HCV in a liver transplant center in Hong Kong. Note: IVDA, intravenous drug abuser; LT, liver transplantation.
phlebotomy (3 samples), and a phlebotomy trolley (2 samples). HCV RNA (genotype 6a) was detected on the inner surface of a single tube holder.
In vitro demonstrations during simulated phlebotomy
Using HCV-contaminated plasma After the simulation test, EDTA tube A (fully filled with HCV- negative blood mimicking a patient’s vein) had a median HCV RNA load of 765IU/mL (range, 85–2,041IU/mL). As expected, the EDTA vacuum-specimen tube B (mimicking the blood collection side) had a higher median HCV RNA load of 10,728IU/mL (range, 5,630–18,127IU/mL). The possible mechanism of retrograde transmission of HCV-contaminated plasma is presented graphi- cally (Fig. 3, A–E) and photographically (Supplementary Fig. 1).
Radionuclide studies using 99mTcO4 99mTcO4 was detected in all saline pre-filled EDTA tubes sug-
gesting reflux from the sleeved-needle back to the patient side (Fig. 4). Furthermore, the amount of 99mTcO4 activity in EDTA tubes was proportional to the degree of radioactivity con- tamination on the rubber sleeve tip of the sleeved-needle and markedly above the background counting of the scanner detector (30 counts per second). In the second experiment, scintigraphic images obtained after release of manual pressure from the saline bag (simulating release of tourniquet) clearly showed reflux of radioactive material into the saline bag (simulating the venous patient side) (Fig. 5).
In vivo demonstration of change in venous pressure during release of a tourniquet
Upon release of the tourniquet, the mean (±standard deviation) venous pressure drop at sitting and lying positions, respectively, were 11.5±3.21mmHg and 12.1±3.73mmHg (right arm). The corresponding values were 12.0±2.4mmHg and 12.0±2.79mmHg (left arm), respectively, and the venous pres- sures were significantly different before and after release of the tourniquet (P<.01).
Phylogenetic analysis of HCV
A phylogenetic tree was constructed using a partial envelope gene (E1–E2 with hypervariable region) of 653 nucleotide positions of HCV strains identified from the index patient, the potential source patient, and the environmental sample from the tube holder. The tree suggested clonality between the virus strains infecting the index case, the potential source patient, and the tube holder (Fig. 6).
Discussion
Hepatitis C virus is primarily transmitted through percutaneous exposure to blood. However, no risk factors are identified in up to 40% of patients with HCV infection.26 While a previous study noted international normalized (prothrombin time) ratio mon- itoring by phlebotomy as a risk factor for nosocomial transmis- sion of HCV, the exact mechanism has never been ascertained.10 We postulate that HCV-positive blood can reflux through the double-end needle from the tip of the rubber sleeve that was inadvertently contaminated during needle insertion after the tube holder was used previously on a HCV-positive source patient (Fig. 4). Vacuum extraction tube systems are designed to reduce percutaneous injury during phlebotomy among healthcare workers.27 It is generally assumed that blood under pressure from the tourniquet-treated vein always flows from the patient toward the vacuum-specimen tube during phlebotomy. However, our in vitro simulated phlebotomy experiment with HCV-positive plasma and radioisotope suggested that retrograde flow of blood is possible. Notably, the rapid removal of vacuum-specimen tubes from the sleeved-needle is often followed by a fine splash of HCV- positive blood that contaminates the inner surface of tube holders. Moreover, during the removal of this double-end needle, the HCV-contaminated sleeve tip inadvertently contaminates the fitting hole of the tube holder and the inner surface of tube holders. When a clean sleeved-needle is inserted through this HCV-contaminated fitting hole, the tip of this clean sleeve
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