HCV & Injection Drug Users in the United States,
1979-2002, An Aging Population
Gregory L. Armstrong, MD
Division of Viral Hepatitis, National Center for
Infectious Diseases, Centers for Disease Control
and Prevention, Atlanta, Ga.
Arch Intern Med. Jan 27,
2007;167:166-173.
“…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
IDU that started in the 1960s and peaked in the
1970s and 1980s…..Among the roughly 2 million US
prisoners, for example, the prevalence of
antibodies to HCV is approximately 15% to
40%....."Baby Boomers," specifically those born
between the late 1940s and early 1960s, are at
considerably higher risk of having ever used
injection drugs than are older or younger
Americans. This finding is consistent with 2
national surveys 4-5 showing this cohort to have
a higher prevalence of HCV infection, for which
the main risk factor is IDU. This cohort is 40
to 60 years old. In 2015, they will be 50 to 70
years old. Almost one third have an annual
family income of at least $50 000. These
observations-including that a 55-year-old person
may be more likely to have used injection drugs
than a 25-year-old person-may challenge
conventional stereotypes of injection drug
users…..Prevention of the long-term consequences
of blood-borne virus transmission is a major
public health priority. Clinicians should
routinely ask patients, regardless of their
demographic characteristics, about drug use,
past and present.16 Clinicians should also
remember that heroin is not the only
recreational drug used by injection. Current
drug users should be encouraged to stop using
drugs. Anyone who has ever used injection drugs,
no matter how infrequently or how remotely in
the past, should be appropriately counseled and
offered testing for the human immunodeficiency
virus, the hepatitis B virus, and HCV.
Clinicians should understand that injection drug
users are a heterogeneous group and that, on
average, they are no longer young….”
INTRODUCTION
Injection drug use (IDU) has an immediate and
deleterious effect on individuals and
communities and provides an efficient mechanism
for transmitting blood-borne viruses, including
human immunodeficiency virus, hepatitis C virus
(HCV), and hepatitis B virus. All 3 can cause
chronic asymptomatic infections that can
eventually lead to severe illnesses years after
the initial infection.1-3 Thus, former injection
drug users remain at risk for the consequences
of IDU long after they have quit using drugs.
This is particularly true with
HCV infection, which is the most common chronic
blood-borne viral infection in the United
States.4-5 A recent survey5 estimated that 4.1
million US residents had antibodies to HCV and
that 3.2 million had a chronic infection.
Approximately half of HCV-infected survey
participants acknowledged having used injection
drugs. Most of these persons (83%) were former
injection drug users, and most (83%) were at
least 35 years old.5 These older former drug
users may not recognize that their behavior
years earlier had put them at risk for HCV
infection.
Therefore, from a public health
perspective, the epidemiology of current IDU and
the epidemiology of past IDU are important. This
study uses a series of large national surveys to
examine trends in IDU over a 23-year period.
ABSTRACT
Background Injection drug use (IDU) is
important in the epidemiology of blood-borne
pathogens. Herein, trends in IDU from 1979 to
2002 are analyzed.
Methods The National Household
Survey on Drug Abuse is an ongoing survey of
drug use among the US population 12 years and
older. Participants were chosen using a
multistage sampling design and interviewed by
written questionnaire (1979-1998) or audio
computer-assisted self-interviewing (1999-2002).
Herein, we examine the prevalence of a history
of IDU at any time in the past (IDU-ever) or
within the past year.
Results In the
2000-2002
surveys, 1.5% (95% confidence interval [CI],
1.4%-1.6%) reported IDU-ever (weighted estimate,
3.4 million persons). Prevalence was highest in
persons aged 35 to 49 years (3.1%; 95% CI,
2.8%-3.4%), was higher in men (2.0%; 95% CI,
1.8%-2.2%) than women (1.0%; 95% CI, 0.9%-1.1%),
and was higher in 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%).
Prevalence decreased with increasing annual
income and educational level. Of all
participants, 0.19% (95% CI, 0.16%-0.23%)
reported IDU within the past year (weighted
estimate, 440 000 persons). Ten years earlier
(1990-1992), 1.6% (95% CI, 1.5%-1.8%) reported
IDU-ever; prevalence did not differ by race.
From 1979 through 2002, the mean age of
participants with IDU within the past year
increased from 21 to 36 years; the age of
participants with IDU-ever increased from 26 to
42 years. From 2000 to 2002, 59.4% of all
persons with IDU-ever were aged 35 to 49 years.
Conclusions The mean age of
injection drug users has increased
substantially. Persons born between the late
1940s and early 1960s have the highest
prevalence of IDU-ever. Self-reported IDU rates
are now lower among young blacks than young
whites.
COMMENT
The demographic characteristics of US 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 IDU that started in the 1960s
and peaked in the 1970s and 1980s. 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 IDU 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.8
This analysis does not address why IDU has
declined among younger cohorts, but other data
suggest the decline is not solely attributable
to switching from injection use to noninjection
use. According to surveys9 of adolescents and
young adults in the United States, illicit drug
use among youth has declined since the late
1970s.
There were also important
differences in temporal trends by race,
particularly among men: the prevalence of IDU
may have peaked in earlier cohorts of black men,
but, in every cohort born since the late 1950s,
the estimated lifetime probability of IDU was
higher among whites than blacks. Furthermore,
the 2000-2002 surveys show much lower rates of
IDU among blacks than whites younger than 50
years. Other data sources also suggest that IDU
by young adults is now lower among blacks than
whites. Among young adults in another recent US
survey,5 self-reported IDU rates were lower
among blacks than whites and the prevalence of
antibodies to HCV was not significantly
different. In a recent study10 among new inmates
in Maryland correctional facilities, the
prevalence of antibodies to HCV among blacks was
less than half that among whites.
The National Household Survey on
Drug Abuse/National Survey on Drug Use and
Health may provide the most representative
assessment of IDU in the United States, but the
survey data are subject to limitations. Most
important, all drug use data are self-reported;
some participants may be reluctant to disclose
drug use despite efforts to encourage
disclosure. In one longitudinal study, for
example, a small proportion of participants who
had disclosed prior drug use on one survey
denied the same drug use when asked on a
subsequent survey. This rate of recanting was
5.1% for marijuana and 7.4% for cocaine.11
Another limitation is the scope of the survey,
which excludes certain important groups, such as
prisoners12 and the homeless not living in
shelters, both of whom have high rates of
illicit drug use. For this reason, the total
number of Americans with current or past IDU is
certainly higher than the number estimated by
this survey. Among the roughly 2 million US
prisoners, for example, the prevalence of
antibodies to HCV is approximately 15% to 40%.12
Assuming, based on this, that 30% of
prisoners have ever engaged in IDU, then the
National Household Survey on Drug Abuse/National
Survey on Drug Use and Health would have
undercounted injection drug users by
approximately 600 000. There are few
representative data on which to base an estimate
of the number of homeless injection drug users.
Furthermore, the trends
highlighted in this assessment may be subject to
certain biases. The survey itself changed during
the 23-year period analyzed herein. Most
questions on the survey have been constant over
time, but several have changed since 1979 and
there have been some important changes in survey
design, such as the expansion of the sampling
frame in the early 1990s and the implementation
of audio computer-assisted self-interviewing in
1999. In addition, the lifetime probability of
IDU model implicitly assumed that mortality
rates among persons who have ever used injection
drugs have been similar to those who have not
used injection drugs. Mortality among active
injection drug users, a minority of this group,
is as high as 1% to 3% per year, largely because
of narcotic overdose, trauma, and AIDS.13-15
Whether mortality rates are also elevated among
those who have quit using injection drugs is
unclear. Higher mortality rates among injection
drug users would reduce the modeled lifetime
probability of IDU among earlier cohorts.
The National Household Survey on
Drug Abuse/National Survey on Drug Use and
Health suggests that the number of persons
actively engaging in IDU has decreased since the
1980s. The number of users is arguably still not
low enough and there is no guarantee against a
future increase. Recent trends, including the
increase in use of amphetamines and prescription
opioids, are concerning in this regard.
An important implication of this
analysis is that "Baby Boomers," specifically
those born between the late 1940s and early
1960s, are at considerably higher risk of having
ever used injection drugs than are older or
younger Americans. This finding is consistent
with 2 national surveys4-5 showing this cohort
to have a higher prevalence of HCV infection,
for which the main risk factor is IDU. This
cohort is 40 to 60 years old. In 2015, they will
be 50 to 70 years old. Almost one third have an
annual family income of at least $50 000. These
observations-including that a 55-year-old person
may be more likely to have used injection drugs
than a 25-year-old person-may challenge
conventional stereotypes of injection drug
users.
Prevention of the long-term
consequences of blood-borne virus transmission
is a major public health priority. Clinicians
should routinely ask patients, regardless of
their demographic characteristics, about drug
use, past and present.16 Clinicians should also
remember that heroin is not the only
recreational drug used by injection. Current
drug users should be encouraged to stop using
drugs. Anyone who has ever used injection drugs,
no matter how infrequently or how remotely in
the past, should be appropriately counseled and
offered testing for the human immunodeficiency
virus, the hepatitis B virus, and HCV.
Clinicians should understand that injection drug
users are a heterogeneous group and that, on
average, they are no longer young.
METHODS
NATIONAL HOUSEHOLD SURVEY ON DRUG
ABUSE
The National Household Survey on Drug Abuse (now
called the National Survey on Drug Use and
Health) has been conducted periodically since
1971 and annually since 1990.6-7 This analysis
uses the public-use data sets from 1979 through
2002 inclusively. Before 1991, the survey
included the civilian noninstitutionalized
population of the contiguous 48 states. In 1991,
the sampling frame was expanded to include
Alaska and Hawaii, residents of noninstitutional
group quarters (eg, college dormitories, group
homes, or civilians dwelling on military
installations), and homeless persons living in
shelters or single-room occupancy hotels.
Persons excluded from the survey, including
members of the military and institutionalized
persons (eg, prisoners and patients in nursing
homes), represent less than 2% of the US
population.7
Survey participants were selected
according to a stratified multistage sampling
design. Final response rates varied from 69% to
89%. To account for oversampling of certain
demographic groups and for other factors, such
as nonresponse, participants were assigned
weights equal to the inverse of their
probability of selection.
Participants were interviewed at
home by trained interviewers using methods to
ensure privacy and confidentiality and to
promote disclosure. For all sensitive questions,
including questions about drug use, participants
were interviewed in a private area and asked to
record, on an answer sheet, responses to
questions read aloud by the interviewer.
Participants did not reveal their responses to
the interviewers, and interviewers were not
allowed to view the completed answer sheets.
From 1999 through 2002, responses to sensitive
questions were gathered by audio
computer-assisted self-interviewing, in which
participants listened to questions through a
headphone and recorded their answers on a touch
screen.7
IDU QUESTIONS
In 1979 and 1982, respondents were asked if they
had ever used heroin with a needle, but were not
asked about any other IDU. Questions were
subsequently added about lifetime use of cocaine
(1985) or amphetamines (1988) by injection.
Beginning in 1990, participants were asked
specifically about lifetime history of IDU with
questions such as, "Have you ever, even once,
used a needle to inject a drug that was not
prescribed for you, or that you took only for
the experience or feeling it caused?" For this
analysis, persons were considered to have ever
used injection drugs (IDU-ever) if they
responded yes to any of these questions.
In the analysis of trends over
time, we divided data into 6 periods of 2 to 3
surveys each. To be as consistent as possible
across the various periods, we defined IDU-ever
in this analysis as ever having used heroin,
cocaine, or stimulants by injection.
Persons were considered to have
had recent IDU if they met 1 of 2 criteria: (1)
the respondent had used heroin, cocaine, or
stimulants by injection during the previous year
(1988-2002) or (2) the respondent had ever used
heroin (1979-1985) or cocaine (1985) by
injection and had used that drug during the
previous year.
RESULTS
The 17 surveys included 452 567 participants.
The number of participants varied from 5624 in
1982 to 58 680 in 2000.
2000-2002 SURVEYS
Of the 168 320 survey participants, 1841 had
ever used injection drugs and 363 had used
injection drugs within the previous year. The
most common drugs used by injection were heroin
(46.0%), cocaine (59.1%), and stimulants
(46.1%). Of all participants who had ever used
injection drugs, 87.2% had used at least 1 of
these 3 drugs. Among the remaining 12.8%, 32.8%
had injected other opiates, 25.4% had injected
anabolic corticosteroids, and 41.9% either
injected other drugs or did not specify the
drugs they had injected (percentages do not
total 100 because of rounding).
The weighted prevalence of IDU-ever
was 1.5%, implying that 3.4 million persons had
used injection drugs during their lifetimes.
The prevalence of IDU-ever was higher among
males than females (P<.001) and was highest
among persons aged 35 to 49 years (3.1%; 95% CI,
2.8%-3.4%; P<.001 for differences by age) (Table
1). Among participants younger than 50 years,
the prevalence of IDU-ever was higher among
non-Hispanic whites (henceforth referred to as
"whites") than non-Hispanic blacks ("blacks") or
Hispanics (P<.001 for both). Among participants
50 years and older, there were no statistically
significant differences between the 3
race/ethnic categories (P>.80 for all
comparisons).
On univariate analysis, IDU-ever
was also associated with birth in the United
States, lower educational level, lower annual
income, and lack of full- or part-time
employment (Table 2). Prevalence was higher
among persons who were divorced, separated, or
never married and was lower among widowers.
Military service was associated with IDU-ever
only among men aged 20 to 49 years. Among
persons aged 20 to 64 years who were employed
full- or part-time, neither random nor nonrandom
drug testing in the workplace was associated
with IDU-ever.
In a multivariate logistic
regression model that included an interaction
term for age and race, IDU-ever was
independently associated with several factors
(Table 3). Adjusted odds ratios were
statistically significantly (P<.05) lower among
blacks than whites in all age groups except the
oldest, in which the adjusted odds ratio was
higher among blacks.
The weighted prevalence of recent
IDU was 0.19% (95% CI, 0.16%-0.23%),
corresponding to 440 000 (95% CI, 360 000-530
000) persons. Recent IDU was more prevalent
among males than females (P=.01), but was not
significantly different by race (Table 2).
Prevalence varied less markedly by age: 0.15%
(95% CI, 0.12%-0.20%) among persons aged 12 to
17 years, 0.28% (95% CI, 0.23%-0.34%) among
persons aged 18 to 49 years, and 0.06% (95% CI,
0.02%-0.16%) among persons 50 years and older.
Recent IDU prevalence varied with
other demographic factors in a manner similar to
that for IDU-ever, except for a lack of
association with military service among 20- to
49-year-old men (Table 2). Also, recent IDU was
less prevalent among full- or part-time
employees aged 20 to 64 years who were subjected
to nonrandom workplace drug testing compared
with those not subjected to drug testing (Table
2).
On multivariate analysis, recent
IDU was independently associated with male sex,
residence in a metropolitan statistical area,
birthplace in the United States, marital status
other than married or widowed, lower educational
level, lower annual family income, and
unemployment. Recent IDU was not associated with
a history of military service. Adjusted odds
ratios were lower among blacks than whites aged
20 to 34 years, but were not statistically
significantly different among participants in
older age groups (Table 3).
1990-1992 SURVEYS
Of the 70 685 participants in the 1990-1992
surveys, the weighted prevalence of IDU-ever was
1.6% (95% CI, 1.5%-1.8%), corresponding to 3.3
million (95% CI, 3.0-3.6 million) persons. The
weighted prevalence of recent IDU was 0.32% (95%
CI, 0.26%-0.40%), corresponding to 650 000 (95%
CI, 530 000-810 000) persons.
The prevalence of IDU-ever was
not statistically significantly different
between whites (1.6%; 95% CI, 1.4%-1.8%), blacks
(2.0%; 95% CI, 1.6%-2.5%), or Hispanics (1.8%;
95% CI, 1.4%-2.4%). Among participants aged 12
to 29 years, IDU-ever was more prevalent in
whites than blacks (2.2% vs 1.5%; P=.02), but
there was no difference for recent IDU (0.6% vs
0.5%; P=.70). Among participants 30 years and
older, IDU-ever was more prevalent among blacks
than among whites (2.3% vs 1.3%; P=.02), as was
recent IDU (0.5% vs 0.2%; P=.04).
TRENDS
Among participants younger than 35 years, the
prevalence of IDU-ever generally decreased
throughout the 1990s (Figure 1A and B). The
decline in prevalence was particularly striking
among young blacks (Figure 1B), in whom the
prevalence was less than 0.3% in the final
period (2001-2002) in all 3 age groups younger
than 35 years. Among white participants 35 years
and older (Figure 1C), the prevalence of
IDU-ever increased markedly. This increase began
in the 35- to 49-year age group around 1980 and
in the 50- to 64-year age group approximately 15
years later, when birth cohorts born in 1945 and
later first became part of these groups. Trends
in the prevalence of IDU-ever in non-Hispanic
black participants 35 years and older varied by
age group (Figure 1D).
A trend of decreasing recent IDU
among participants younger than 35 years (Figure
2A and B) was particularly striking among black
participants (Figure 2B). Among older
participants, almost all recent IDU was in the
35- to 49-year age group (Figure 2C and D).
>From 1979 to 2002, the mean age
of participants with recent IDU increased from
21 to 36 years (Figure 3). During the same
period, the mean age of participants with
IDU-ever increased from 26 to 42 years.
LIFETIME PROBABILITY OF IDU
Lifetime probability of engaging in IDU,
estimated from a logistic regression model that
included age, sex, race, and birth cohort as
dependent variables, showed strong cohort
effects (Figure 4) and peaked approximately 5 to
10 years earlier among blacks compared with
whites. From cohorts born before 1955, trends
among Hispanics were generally similar to those
among whites. For later cohorts, the lifetime
probability of IDU was lower among Hispanics.
Among black cohorts, the probability of IDU was
higher than among whites for cohorts born before
1955, but was substantially lower for cohorts
born after 1955. The probability of IDU was
almost always higher among men than among women,
although differences between men and women
progressively narrowed over time.
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