While many anti-drug campaigns have warned of the hazards of sharing hypodermic needles, the new study found that injection drug users who shared cookers--containers used to dissolve and heat illicit drugs including heroin and cocaine--were four times more likely to contract HCV. Those who shared cotton filters more than doubled their risk of contracting the virus. Sharing syringes and rinse water also boosted risk, but not significantly.

"In most injection sessions, drugs are placed in a cooker and dissolved in water. The solution is then drawn into a syringe through a cotton filter to strain out 'impurities,"' Dr. Lorna E. Thorpe of the University of Illinois at Chicago and colleagues explain in the April issue of the American Journal of Epidemiology.

Thorpe's team followed 702 injection drug users from 1997 to 1999. All of the young adults in the study provided blood samples and those who did not already have HCV were retested 6 months and 1 year later.

About one quarter of the drug users were already infected with HCV at the beginning of the study, the authors report.

During the study period, 29 more became infected with the virus. After adjusting for the sharing of syringes, the researchers calculated that injection drug users who shared cookers were more than three times more likely to contract HCV. Sharing cotton filters more than doubled a person's risk of contracting HCV, the report indicates.

"This study provides...evidence that sharing of drug injection paraphernalia other than syringes may cause transmission of HCV among injection drug users," Thorpe and colleagues write.

"Prevention messages and campaigns should be revised to alert active injection drug users to the importance of reducing or eliminating all equipment-sharing practices," they conclude.

Currently in the US, injection drug users are the group at highest risk for infection with HCV, with experts attributing more than 60% of new HCV cases to people who inject illicit drugs.

HCV causes deterioration of the liver, or cirrhosis, in about 20% of people with chronic infection, and it can be fatal. A 6-to 12-month course of interferon treatment, sometimes given along with the antiviral drug ribavirin, wipes out HCV in about 40% of infected people.

SOURCE: American Journal of Epidemiology 2002;155:645-653.