To the Editor: Researchers studying HIV risks in injecting drug users rarely assess characteristics of injection equipment. Implicit in this omission is the notion that differences in injection equipment have little or no impact on HIV risk. Needles and syringes used by drug injectors may vary in a number of attributes, including syringe volume, type of syringe, and gauge and length of needle. Several observers(1-3) have noted that syringes with detachable needles retain substantially more blood than integral cannula syringes with permanently attached needles and may thus transmit substantially more virus when shared. The bore of a 28-gauge needle is much smaller than the bore of a 25-gauge needle, thus restricting the flow of liquid and increasing the time required to rinse a syringe with a 28-gauge needle. We examined the effect of needle gauge on the minimum time required to disinfect a syringe with bleach.
We compared the time required to completely fill and expel bleach twice from 1-ml insulin syringes with 25-gauge, 26-gauge, and 28-gauge needles. We selected five 1-ml insulin syringes with 25-gauge detachable needles, five 1-ml insulin syringes with 26-gauge detachable needles, and five 1-ml insulin syringes with 28-gauge permanently attached needles. Each syringe was filled to the 1-ml mark with bleach, the bleach was expelled, the syringe was refilled with bleach, and the bleach was again expelled. The process was repeated 10 times with five different syringes with each gauge needle. Cleaning time was measured using a digital stop watch that measured increments of 0.01 second. Recorded times were rounded to the nearest 0.1 second. Analysis of variance was performed to compare the time required to rinse syringes with different gauge needles. The Tukey method was used to adjust for multiple comparisons.
As shown in Table 1, the mean number of seconds required to fill and expel bleach twice was 15.7 seconds with a 25-gauge needle, 19.2 seconds with a 26-gauge needle, and 26.9 seconds with a 28-gauge needle. All pairwise comparisons were significant at a family error rate of p < 0.001. Gauge of needle explained 92% of the variance in cleaning time.
Our findings illustrate how a minor difference such as the gauge of the needle influences the time required to disinfect a syringe. Shapshak et al.(4) demonstrated that undiluted household bleach completely inactivates HIV in a syringe following an exposure time of 30 seconds. They also demonstrated that bleach does not completely inactivate HIV in a syringe following an exposure time of 15 seconds. Shapshak et al. used a 1-ml insulin syringe with a 25-gauge needle in their experiments. The finding that it takes a minimum of 25 seconds to rinse a syringe with a 28-gauge needle suggests that these smaller needles may inadvertently compel compliance or near-compliance with recommended exposure times, thus increasing the effectiveness of bleach disinfection. Investigators studying HIV risk behavior should include characteristics of injection equipment-type of syringe, volume of syringe, and gauge of needle-as routine items on data collection instruments.
William A. Zule
David P. Desmond
Department of Psychiatry; University of Texas Health Science Center at San Antonio; San Antonio, Texas
1. Zule WA, Ticknor-Stellato KM, Desmond DP, Vogtsberger KN. Evaluation of needle and syringe combinations. J Acquire Immune Defic Syndr Hum Retrovirol
2. Grund JP, Friedman SR, Stern LS, et al. Syringe-mediated drug sharing among injecting drug users: patterns, social context and implications for transmission of blood-borne pathogens. Soc Sci Med
3. Seamark R, Gaughwin M. Jabs in the dark: injecting equipment found in prisons, and the risks of viral transmission. Aust J Public Health
4. Shapshak P, McCoy CB, Shah SM, et al. Preliminary laboratory studies of inactivation of HIV-1 in needles and syringes containing infected blood using undiluted household bleach. J Acquire Immune Defic Syndr Hum Retrovirol