CROI 2010: Hepatitis C Virus Can Survive in Syringes Up to 2 Months under Favorable Conditions

Hepatitis C virus (HCV) can survive under certain conditions for prolonged periods in syringes used to inject drugs, thereby increasing the potential for HCV transmission, researchers reported at the 17th Conference on Retroviruses and Opportunistic Infections (CROI 2010) last week in San Francisco. These findings are important for shaping needle exchange policies and practices.

HIV and HCV are transmitted in some of the same ways, but HCV transmission typically occurs first in people exposed to both viruses, such as injection drug users who share needles and syringes

Elijah Paintsil and colleagues from Yale School of Medicine designed a study to test the hypothesis that the high prevalence of HCV among injection drug users may be due to the fact that the virus remains viable for long periods in contaminated syringes.

HCV transmission occurs 10 times more often than HIV transmission from an accidental needle stick, the investigators noted as background, and harm reduction measures such as needle exchange programs that have dramatically reduced new HIV infections have had a lesser effect on HCV incidence.

The study evaluated 2 types of syringes:

• A low-volume insulin syringe with a permanently attached needle holding 2 microliters of blood;
• A higher-volume tuberculin syringe with a detachable needle holding 32 microliters of blood.

The researchers developed a new microculture assay for measuring viral viability in syringes, using a genotype 2 HCV strain that can live and replicate in a laboratory cell line. They first loaded syringes with HCV-spiked blood, then depressed the plunger to expel it; this process simulates "booting," when a user draws blood up into the syringe to mix with the drug before injecting it.

Either immediately or after a storage periods of up to about 2 months, the investigators flushed out the syringes and introduced the recovered virus into cell cultures. Syringes were stored at 3 different temperatures: 40ºF (4ºC), the temperature of an average refrigerator; 72ºF (22ºC), or room temperature in a temperate climate; and 98ºF (37ºC), equivalent to body temperature or a very warm climate.

Results

• Exposed cell cultures showed varying levels of HCV infectivity.
• The likelihood of finding infectious virus in low-volume syringes decreased rapidly:
  • No remaining viable virus after 1 day in syringes stored at 98ºF;
  • No viable virus after 3 days in syringes stored at 72ºF;
  • No viable virus after 7 days in syringes stored at 40ºF.
• For high-volume syringes, the pattern was less consistent, with the likelihood of finding infectious virus falling until day about 7, then fluctuating for several weeks before eventually dropping toward 0 by day 63.
• At 40ºF, viable HCV was detected in about two-thirds of low-volume syringes at day 1, about 25% at day 3, and about 5% at day 7.
• At the same temperature, viable virus was detected in nearly all high-volume syringes at day 7, about half did at day 35, and approximately 5% at day 63.
• Even at the 2 higher temperatures, a small proportion of high-volume syringes still contained infectious HCV at day 63.
• The titer or amount of viable HCV in low-volume syringes showed an initial rapid decrease followed by a slower decrease, becoming undetectable between days 2 and 3 at 98ºF and by day 3 at 72ºF, but at 40ºF remaining at a low level at day 7.
• The virus titer in high-volume syringes declined during the first 1-2 weeks, then leveled off and remained at a low but stable level at all temperatures. 

Based on these findings, the researchers concluded that survival of viable HCV is dependent on syringe type, as those with detachable needles "appear far more likely" to transmit the virus.

"Lower temperature preserves HCV viability in low void volume syringes more than in high void volume ones," they continued. "HCV and HIV survival in low void volume syringes show similar time course, but HCV appears to survive longer than HIV in high void volume syringes."

Speaking at a press conference following the presentation, Paintsil said it is "probably advisable" for needle exchange programs to offer the smaller insulin syringes, but acknowledged that individuals who inject hormones (e.g., transgender people, body-builders) prefer larger ones.

The most important thing, he emphasized, is to distribute enough needles so that people do not have to share, and to promptly remove used needles from circulation.

In response to a question about whether HCV transmission among injection drug use varies between warm and cold climates or between summer and winter, he said that was excited about exploring this possibility.

Yale School of Medicine, New Haven, CT.

2/23/10

Reference

E Paintsil, H He, C Peters, and others. Survival of HCV in Syringes: Implication for HCV Transmission among Injection Drug Users. 17th Conference on Retroviruses and Opportunistic Infections (CROI 2010). San Francisco. February 16-19, 2010. Abstract 168.