Recent research from the Yale School of Public Health indicates that a widely accepted strategy to decrease the transmission of the hepatitis C virus through needles may not be as effective as hoped.
The study clarified the effectiveness of low-dead-space needles and syringes which are recommended preventative measures against contracting HCV from injections. Although the researchers observed a moderate decrease in transmission with LDS syringes when compared to high-dead-space syringes, it was nowhere near as low as the transmission rate in insulin syringes, the safer standard, said Robert Heimer GRD ’88, professor of epidemiology and pharmacology at the Yale School of Public Health and co-author of the study.
“It’s a better alternative, but it’s not good enough,” Heimer said.
Syringes and needles used to inject drugs come in many forms; insulin syringes, for example, have fixed needles that cannot detach, while other syringes have detachable needles. Syringes with detachable needles are larger and often used in order to attain higher injection volumes, Heimer said.
However, syringes with detachable needles have high dead space, a measure of how much liquid is retained in the joint between the syringe and needle even after injection. These needles can retain over 20 times more potentially infectious liquid than fixed-needle syringes, Heimer said.
Various LDS needles and syringes have been designed to minimize the dead space — for example, some include a plunger that extends all the way to the base of the syringe, said William Zule, a fellow and senior health analyst at RTI International who was not involved in the study.
The LDS needles and syringes have been recommended by public health organizations as a safer alternative to HDS needles and syringes. The World Health Organization recommends that needle and syringe exchange programs offer LDS syringes, and the Global Fund to Fight AIDS, Tuberculosis and Malaria supports the purchases of LDS syringes, said Sarah Russell, coordinator of the communications department at the WHO.
In the study, Heimer and his colleagues tested various combinations of LDS and HDS needles and syringes and compared them to an insulin syringe control. First, they measured the amount of residual liquid in each syringe-needle pair. Then, they loaded each pair with HCV-infected plasma and tested for the presence of HCV immediately after injection and after storing the syringe for a week at room temperature.
Their results showed that, as expected, insulin syringes with fixed needles retained only 1.3 microliters, the lowest volume among the combinations tested. It also had the lowest infectivity — only 47 percent of the syringes were HCV positive. HDS syringes retained over 10 times as much liquid and 98 percent of the syringes were HCV positive. However, among the LDS pairs, which were designed to decrease the transmission of HCV, 65 to 93 percent of the syringes were still HCV positive.
“[If someone uses a contaminated LDS syringe,] they’re still going to be at considerable risk of being exposed to HCV,” Heimer said.
According to the study, the presence of HCV dropped in all syringes with time in storage. LDS needles were shown to be somewhat more effective than LDS syringes, but still allowed for greater transmission of the virus than the insulin syringes.
Zule noted that the retention of liquid in the syringes has important implications outside of drug use as well — dead space causes dosing problems when small volumes of medicine are being injected, he said. He has studied the same phenomenon through simulations, but without the laboratory measurements of HCV retention that the Yale study included.
“The evidence from [Heimer’s] study is critical,” Zule said. “It points to the limits of what we can achieve.”
Zule said he does not think these results mean that achieving effective LDS syringes is impossible. Rather, he said LDS syringes are a step in the right direction, but not the final solution.
Similarly, Russell said, although LDS syringes may not be 100 percent safe, the reduction in risk is still substantial.
Zule said he thinks the LDS syringes would be more effective at preventing HIV transmission, because the virus is present in lower quantities in the blood. Heimer said he is still in the process of carrying out a parallel study to measure the effectiveness of LDS needles and syringes in decreasing the transmission of HIV.
He said his next steps will be to talk to manufacturers about ways to further decrease the dead space in syringes with detachable needles and to advocate for increased access to drugs that treat HCV infections.
“If you want to control the epidemic, we need more clean syringes,” Heimer said. “People will continue to inject drugs, so we need ways to keep those people safe.”
According to the Centers for Disease Control and Prevention, there were over 29,000 cases of acute HCV in the U.S. in 2013.