By Liz Highleyman

Sharing of needles and other equipment for drug injection is an efficient means of transmitting blood-borne infections such as HIV, hepatitis C virus (HCV), and hepatitis B virus (HBV). HCV is more easily transmitted than HIV through needle-sharing, and studies indicate that injection drug users (IDUs) tend to become infected with HCV soon after they start injecting.

In the January 27, 2007 Archives of Internal Medicine, Gregory L. Armstrong, MD, of the Centers for Disease Control and Prevention (CDC) reported on an analysis of characteristics of IDUs in the U.S. between 1979 and 2002.

Data was obtained from the National Household Survey on Drug Abuse, an ongoing survey of drug use among U.S. adults aged 12 years and older. Participants were chosen using a multistage sampling design and interviewed using written questionnaires (1979-1998) or computer-assisted self-interviews (1999-2002). Importantly, the survey excluded members of the military and institutionalized persons such as prisoners and nursing home patients.

Results

• In the 2000-2002 surveys, 1.5% of study respondents (95% CI 1.4%-1.6%) reported ever injecting drugs, for an estimated total of 3.4 million persons.

• The survey showed that injection prevalence was:

- highest among individuals aged 35 to 49 years (3.1%; 95% CI 2.8%-3.4%);

- higher among men (2.0%; 95% CI 1.8%-2.2%) than women (1.0%; 95% CI 0.9%-1.1%);

- higher among whites (1.7%; 95% CI 1.5%-1.8%) than blacks (0.8%; 95% CI 0.7%-1.1%) or Hispanics (1.1%; 95% CI 0.8%-1.4%).

• Injection prevalence decreased with increasing annual income and educational level.

• Of all participants, 0.19% (95% CI 0.16%-0.23%) reported injecting drugs within the past year, for an estimated total of 440,000 persons.

• 10 years earlier, in the 1990-1992 period, 1.6% (95% CI 1.5%-1.8%) of respondents reported ever injecting drugs, and prevalence did not differ by race.

• From 1979 through 2002, the mean age of participants who reported drug injection within the past year increased from 21 to 36 years.

• The mean age of participants who reported ever injecting drugs increased from 26 to 42 years.

• From 2000 through 2002, 59.4% of all persons who reported ever injecting drugs were 35 to 49 years old.

Conclusion
"The mean age of injection drug users has increased substantially," Dr. Armstrong concluded. "Persons born between the late 1940s and early 1960s have the highest prevalence of [a history of injection drug use]. Self-reported injection drug use rates are now lower among young blacks than young whites."

In his discussion, he noted that, "The demographic characteristics of U.S. injection drug users changed substantially during the 23-year period of this analysis. The marked increase in the mean age of injection drug users -- an increase of 16 years for those who have ever used injection drugs and 15 years for those who are actively using drugs -- is consistent with the epidemic of [injection drug use] that started in the 1960s and peaked in the 1970s and 1980s."

He added that, "The increasing mean age and the fact that middle-aged adults are more likely than young adults to have ever used injection drugs would be consistent with a large decline in the initiation of [injection drug use] in the early 1990s, which could at least partly account for the large decrease in the incidence of acute hepatitis C observed in the United States at that time."

Based on these results, Dr. Armstrong said that healthcare providers must recognize that "injection drug users are a heterogeneous group and that, on average, they are no longer young." He recommended that anyone who has ever injected drugs -- no matter how infrequently or how long in the past -- should be offered testing for HIV, HBV, and HCV.

02/13/07

Reference
G L Armstrong. HCV and Injection Drug Users in the United States, 1979-2002, An Aging Population. Archives of Internal Medicine 167(2): 166-173. January 27, 2007.