REGULAR OUTPATIENT MEDICAL AND DRUG ABUSE CARE AND SUBSEQUENT

HOSPITALIZATION OF PERSONS WHO USE ILLICIT DRUGS

Context: Patients and the public could benefit from identification of
factors that prevent drug users' heavy reliance on inpatient care;
however, optimal health care delivery models for illicit drug users
remain ill-defined.

Objective: To evaluate associations of outpatient medical and drug
abuse care with drug users' subsequent hospitalization rates.

Design and Setting: Retrospective cohort study of data from
longitudinally linked claims for all ambulatory physician/clinic
services and drug abuse services covered by the New York State
Medicaid program.

Subjects: A total of 11 556 human immunodeficiency virus
(HIV)-positive and 46 687 HIV-negative drug users.

Main Outcome Measures: Hospitalization in federal fiscal year (FFY)
1997 compared by 4 patterns of care in FFY 1996: regular drug abuse
care (6 months in 1 program), regular medical care(35% of care from 1
clinic, group practice, or individual physician), both, or neither.

Results: Hospitalization occurred in 55.6% of HIV-positive and 37.5%
of HIV-negative drug users, with a mean of 27.5 and 24.5 inpatient
days, respectively. In HIV-positive drug users, the adjusted odds
ratio (AOR) for hospitalization was lowest among those with both
regular medical and drug abuse care (AOR, 0.76; 95% confidence
interval [CI], 0.67-0.85) followed by those with regular medical care
alone (AOR, 0.82; 95% CI, 0.74-0.91) and regular drug abuse care alone
(AOR, 0.85; 95% CI, 0.76-0.96) vs those with neither.

In HIV-negative drug users, the AOR of hospitalization was lower for
those with regular medical and drug abuse care (AOR, 0.73; 95% CI,
0.68-0.79), regular drug abuse care alone (AOR, 0.71; 95% CI,
0.66-0.76), and regular medical care (AOR, 0.91; 95% CI, 0.86-0.95) vs
those with neither.

Both types of care showed favorable effects for all but drug
abuse?related hospitalizations.

Conclusion Our data indicate that regular drug abuse care with
regular medical care for drug users is associated with less subsequent
hospitalization.

JAMA. 2001;285:2355-2362

Users of illicit drugs have complex health care needs.1-5 Yet, many
drug users receive medical care only when crises arise that require
emergency department care or hospitalization.1, 6-9 Drug users are
twice as likely to visit an emergency department and nearly 7 times
more likely to be hospitalized than comparably aged persons who do not
use illicit drugs.10 Even in Canada, where citizens have access to
universal health insurance, substance abuse accounts for approximately
8% of hospitalizations.11 In the United States, public payers are
responsible for much of the hospitalization costs for persons with
substance abuse.9, 12 Once hospitalized, drug users also appear to
have longer lengths of stay. In a cohort of human immunodeficiency
virus (HIV)?infected Medicaid enrollees, we reported that drug users
averaged 2 weeks longer in the hospital than nonusers following
initial acquired immunodeficiency syndrome (AIDS) diagnosis.13
Patients and the public stand to benefit from the identification of
factors that prevent drug users' heavy reliance on inpatient care.

Medical care and drug abuse treatment in ambulatory settings may
reduce use of inpatient services by providing timely management of
medical conditions and by preventing drug abuse?related complications.
Having a regular source of medical care has been associated with
improved delivery of preventive care and reduced substance abuse in a
poor population.14 Having a regular source of care has also been
related to lower use of hospital services by HIV-positive persons.15
Outpatient drug abuse treatment frequently offers an array of services
that address not only drug abuse but also the social, psychological,
and legal needs of this population.16 Regular ambulatory substance
abuse treatment has been found to improve survival of drug users17 and
to reduce HIV risk behaviors.18

We hypothesized that a combination of regular medical care with
regular drug abuse treatment would show a protective association with
hospital use. To explore this hypothesis, we examined the association
of medical and drug abuse care with hospitalization in a cohort of
HIV-positive and HIV-negative drug users enrolled in the New York
State (NYS) Medicaid program.

METHODS

Data Sources

We conducted a retrospective cohort study of drug users enrolled in
the NYS Medicaid program from federal fiscal years 1996 through 1997.
Data were from longitudinally linked claims for all ambulatory
services from physicians and clinics and drug abuse services covered
by the Medicaid program. These files provide information on various
covered services: inpatient, pharmacy, home health care, selected case
management, and laboratory. The institutional review boards of Thomas
Jefferson University, the New York State Department of Health, and
Montefiore Medical Center approved the study.

Study Population

We identified Medicaid claims associated with illicit drug use, HIV
infection, and AIDS using previously tested algorithms developed by
our group.19-21 The algorithm to screen claims for illicit drug use
searches for International Classification of Diseases, Ninth Revision,
Clinical Modification (ICD-9-CM) codes for heroin, cocaine,
amphetamine, or unspecified illicit drug dependence or abuse; for
Medicaid services (or rate codes) for methadone treatment or medically
supervised drug abuse treatment; and for New York State diagnosis
related groups (DRGs) for inpatient drug detoxification. Persons
infected with HIV were identified by another case-finding method that
searches for at least 1 of the following: (1) 1 or more pharmacy
claims for an antiretroviral drug, (2) 1 or more inpatient stays with
a diagnosis of an AIDS-defining condition or HIV-related DRG, or (3)
at least 2 occurrences separated by more than 30 days of: an
outpatient physician or clinic visit with an HIV-related or
AIDS-defining diagnosis, an HIV-specific outpatient care rate code, or
inpatient stay for an HIV-related condition such as pneumonia.

Our initial longitudinal Medicaid analysis file included 78 943
persons who met the illicit drug use algorithm, were 13 through 59
years of age in 1996, and were enrolled continuously in Medicaid for
10 months or more in 1996. Of this group, 77 618 had any outpatient
visit(s) in 1996 to permit analysis of patterns of care. Of these, 59
104 were enrolled in Medicaid for 10 months or more in 1997 and 59 092
had demographic information. After excluding women with evidence of
pregnancy or delivery in 1997, the final study population totaled 58
243 persons.

To gauge the operating characteristics of these Medicaid claims
case-finding algorithms, we conducted a validation study using a
sample of patients treated at Montefiore Medical Center in the Bronx,
NY. From outpatient chart review supplemented by self-report data from
research questionnaires for some drug users, 207 Medicaid enrollees in
1996 were classified into 4 groups: using illicit drugs, never using
illicit drugs, HIV-positive, and HIV-negative. According to these
classifications, the NYS Medicaid claims algorithm had a sensitivity
of 0.86 and a specificity of 0.87 for identifying drug abuse, and
these characteristics were 0.96 and 1.0, respectively, for detecting
HIV infection. We conducted a detailed examination of Medicaid claims
for the 14 individuals who were classified as drug users according to
Medicaid data but classified as nonusers according to Montefiore data
sources. This review showed that 11 had numerous (ie 10) outpatient
visits for drug abuse treatment and/or at least 1 inpatient stay with
the diagnosis of illicit drug dependence, all from providers outside
of the Montefiore system.

Thus, they were most likely misclassified by the Montefiore-only data
sources.

Classification of Outpatient Patterns of Care

We categorized each drug user's pattern of outpatient care based on
Medicaid claims in 1996 as regular drug abuse care only, regular
medical care only, both, or neither.

Regular drug abuse care was defined as care from a single methadone or
drug-free treatment program for at least 6 contiguous calendar months
in 1996. We applied a 6-month criterion because a minimum length of
stay for effective methadone treatment according to Ball and Ross22 is
6 months and studies of treatment for cocaine abuse similarly define
treatment periods as 6 to 12 months.23 At least 3 weekly claims for
drug abuse treatment per month were required to fulfill criteria for
regular drug abuse care; this allows for at most a 1-week lapse in
treatment.

During hospital stays, patients were classified as having continued
their drug treatment if they had already started drug treatment before
the hospitalization. In the rare instances when outpatient drug abuse
treatment claims are submitted daily, we considered 15 or more such
claims from the same provider in each 30-day interval of
nonhospitalized days within a 6-month calendar period as indicating
regular drug abuse care.

We studied 2 types of ambulatory drug abuse treatment: methadone
maintenance treatment clinics and medically supervised (Title 1035 or
"medically supervised drug-free") clinics.

These clinics can be part of large programs with multiple sites but we
considered care within the same program as continuous, in part because
Medicaid claims often do not distinguish separate providers within
multisite practices.

We did not consider clinics that provided only alcohol abuse
treatment.

We also did not consider detoxification, residential, and
non?medically supervised ambulatory programs in this analysis because
we were interested in longitudinal ambulatory services supervised by a
professional. Furthermore, detoxification treatment for
opiate-addicted persons has been reported to be less successful in
reducing drug-related behaviors than standard methadone treatment.24
We also did not consider physicians who provide drug abuse treatment
in private offices because they delivered less than 10% of all drug
abuse care reimbursed by NYS Medicaid in 1998 (Peter Gallagher, NYS
Department of Health, oral communication, January 2001).

A regular source of medical care was defined as a clinic or physician
visited by a study subject at least twice as an outpatient during 1996
and delivering more than 35% of all outpatient encounters from primary
care physicians, obstetrician-gynecologists, or medical subspecialists
in that year.15 These providers could be clinics, group practices, or
individual physicians. When a patient saw 2 providers for the same
proportion of visits, we used a previously developed hierarchy of
specialties to select the regular medical provider.15 In a previous
study of HIV-positive Medicaid enrollees, we found no significant
differences in outcomes from 2 cutpoints(35% and 50%) for defining
regular medical care.15 Using the "greater than 35%" cutpoint avoids
misclassification of patients with more than one third of their care
from a given provider as having no regular medical care.

Main Outcome Variable

The study-dependent variable was 1 or more hospitalization during
federal fiscal year 1997. Hospitalizations were determined from
Medicaid claims for inpatient stays of at least 1 day. Using ICD-9-CM
diagnosis codes (up to 5 per hospital claim), we also classified
hospitalizations into 4 groups: drug abuse related (eg, illicit drug
poisoning or medical complications of drug abuse such as
endocarditis), alcohol related (eg, pancreatitis, cirrhosis,
Mallory-Weiss tear), mental health?related (eg, depression,
schizophrenia), and medical (eg, HIV-related and general medical
conditions such as pneumonia, sickle cell crisis, diabetes, congestive
heart failure). A hospital stay categorized into more than 1 of these
clinical types was considered in the analysis of each relevant
hospitalization type. Unclassified types of hospitalizations such as
injuries were placed in an "other" category.

A complete list is available from the authors.

Other Study Variables

Patient demographic characteristics were obtained from Medicaid claims
and eligibility files including those for age, sex, and NYS region of
residence. Residence was classified from ZIP codes as rural, small
city, upstate urban, New York City suburb, or New York City. New York
State Medicaid files do not contain reliable data on ethnicity.

Data on comorbid conditions were also obtained from ICD-9-CM codes on
inpatient and outpatient claims files in 1996. We used only 1996 data
to measure comorbid conditions to avoid analytic difficulties
associated with concurrent measurement of comorbidity and
hospitalization outcomes. Using diagnoses on Medicaid claims of
AIDS-defining conditions (eg, Pneumocystis carinii pneumonia or
tuberculosis) or HIV-related complications such as an episode of
pneumonia, we determined the HIV clinical stage of each patient.

We also identified specific types of drug abuse, psychiatric disease
(eg, depression, non?drug-related psychoses, anxiety disorders), and
chronic diseases other than HIV (eg, diabetes, hypertension, asthma,
sickle cell anemia) (Table 1). Lastly, we included a variable for the
total number of hospital days in 1996 in our models as a proxy for
unmeasured health status.

Analyses

All analyses were conducted separately for HIV-positive and
HIV-negative patients. After examining bivariate associations between
covariates and hospitalization end points, we estimated multivariable
regression models with any hospitalization (logistic regression) in
1997 as the dependent variable. We also estimated separate logistic
regression models for each clinical type of hospitalization.

To assess potential selection effects for the models with any
hospitalization as the dependent variable, we also conducted a
propensity score analysis that considered each patient's propensity of
being in a particular outpatient care group.25 To determine the
propensity scores, we conducted a polychotomous logistic regression
analysis with a variable indicating pattern-of-care group membership
as the dependent variable and the variables listed in Table 1 as the
independent variables.

Since there are 4 pattern-of-care groups, we derived 3 propensity
scores.

We then repeated the multivariable analyses using any hospitalization
as the outcome with the 3 propensity scores, including indicators for
quintiles of each propensity score and the pattern-of-care grouping
variable.

We compared these results to those of the logistic regression model
including separate patient characteristics. Analyses were performed
using SAS version 8.0 (SAS, Cary, NC).

RESULTS

Table 1 shows the baseline characteristics of the 11 556 HIV-positive
and 46 687 HIV-negative drug users in the analysis.

Approximately 30% of the study population had regular drug abuse care
alone or with regular medical care in 1996 but a higher proportion of
HIV-positive drug users had regular care of both types.

More than half of the study population had regular medical
care.

Associations of Patterns of Care With Hospitalization in
1997

In 1997, more than half of the HIV-positive and one third of the
HIV-negative group had at least 1 hospitalization (Table 2). Those who
were hospitalized spent nearly 1 month as an inpatient over the course
of 1997. In both groups, those with regular drug abuse care only or
with regular medical care had the lowest proportions of any
hospitalization in 1997. Similar relationships of the patterns of
ambulatory care with average number of inpatient days in 1997 were
observed in both groups.

The proportions of persons in both groups who were at least 50 years
old or who had another chronic disease such as diabetes were higher
among those with regular drug abuse care and regular medical care than
for those in the other patterns of care (data not shown). Among
HIV-negative persons, only medical care was more likely for those with
heroin or cocaine abuse or dependence, drug dependence of unspecified
type, acute drug-related complication (eg, cellulitis, drug
withdrawal, phlebitis), alcohol abuse, and alcohol-related
complication (eg, pancreatitis, acute alcoholic hepatitis). The
distribution of these characteristics by pattern of care for
HIV-positive drug users was less skewed.

Among HIV-positive drug users, regular drug abuse care with regular
medical care was associated with nearly a 25% reduction in the
adjusted odds of hospitalization vs neither type of care, while the
associations were somewhat weaker for either type of care alone (Table
3). Among HIV-negative drug users, regular drug abuse treatment alone
or with regular medical care was associated with a more than 25%
reduction in the adjusted odds of hospitalization (0.71 and 0.73,
respectively). However, we observed a greater benefit associated with
regular medical care alone for the HIV-positive drug users (ie,
adjusted odds of hospitalization reduced by 18%, vs 9% for
HIV-negative).

In both groups, the adjusted odds of hospitalization were greater for
persons with drug abuse or medical complications during 1996, the
baseline year. Of these factors, acute alcohol-related complications
were associated with the greatest increase in the likelihood of any
hospitalization. As expected, hospitalization in 1996 was strongly
related to the risk of hospitalization in 1997.

For both HIV-positive and HIV-negative groups, we estimated models
predicting the probability of an individual receiving each of the
patterns of care and included the propensity scores grouped in
quintiles from these models as independent variables in models
predicting any hospitalization (data not shown). Among HIV-positive
persons, the adjusted odds ratio (AOR) of any hospitalization from the
propensity score analysis was also lowest for persons with both types
of care (AOR, 0.76; 95% confidence interval [CI], 0.68-0.86), followed
by only regular medical care (AOR, 0.82; 95% CI, 0.74-0.91) and only
drug abuse care (AOR, 0.84; 95% CI, 0.75-0.95), compared with neither
type of care. In the model including the propensity score variables
for the HIV-negative group, the adjusted odds were similar for persons
with both regular drug abuse care and regular medical care (AOR, 0.67;
95% CI, 0.63-0.71) and those with only drug abuse treatment (AOR,
0.66; 95% CI, 0.61-0.71) vs persons with neither form of care. Only
regular medical care was less protective (AOR, 0.90; 95% CI,
0.86-0.94). These results closely resemble those for the model that
did not include the propensity scores (Table 3).

Association of Pattern of Care and Specific Types of
Hospitalization

Hospitalizations for the study population in 1997 were categorized by
discharge diagnoses on claims into 4 non?mutually exclusive clinical
categories (Table 4). All but 2843 (8.5%) hospitalizations were in 1
or more of these categories. Medical hospitalizations were the most
frequent type. Regardless of HIV status, regular drug abuse care with
or without regular medical care was associated with a reduction in the
adjusted odds of alcohol-related and mental health?related
hospitalizations. Regular drug abuse care with or without regular
medical care was associated with an approximately 15% reduction in
medical hospitalization in both groups, while in the HIV-positive
group only medical care was similarly protective.

The only significant associations with drug abuse?related
hospitalizations were found for drug abuse care alone, which was
associated with higher adjusted odds for this type of hospitalization
in HIV-negative persons.

Because a drug abuse?related hospitalization could be for
detoxification (a potentially desirable reason for hospitalization) we
repeated the analysis excluding hospitalizations for which
detoxification was indicated as a procedure during the hospitalization
(n = 456). In both groups, this model showed more protective
associations of regular outpatient care with drug abuse?related
hospitalization. In the HIV-positive group, the patterns of care were
associated with the following AORs for this outcome: regular drug
abuse care alone (AOR, 0.93; 95% CI, 0.78-1.11), regular medical care
alone (AOR, 0.87; 95% CI, 0.77-1.00), and both patterns of care
together (AOR, 0.76; 95% CI, 0.63-0.91). In the HIV-negative group,
the patterns of care were associated with the following results:
regular drug abuse care alone (AOR, 0.89; 95% CI, 0.79-1.01), regular
medical care alone (AOR, 0.96; 95% CI, 0.90-1.03), and both patterns
of care together (AOR, 0.89; 95% CI, 0.79-0.91).

COMMENT

Our study affirms the enormous demand by users of illicit drugs for
hospital care but also sheds light on possible solutions to this
problem. In our population-based cohort of nearly 60 000 drug users,
more than half of the HIV-positive group and one third of the
HIV-negative group were hospitalized in 1997 and those hospitalized
spent nearly 1 month as an inpatient over the course of the year. This
high use of hospital care not only reflects substantial morbidity in
this Medicaid-enrolled population but is also extraordinarily costly.

French et al26 reported that out-of-treatment chronic drug users
generated about $1000 annually in excess service use per individual
compared with nonusers, with most of this cost due to greater
inpatient care and emergency department use. That study also found
that drug users used fewer ambulatory services than nonusers.

Nearly 50% of our cohort did not have a regular source of medical
care. In addition, only 30% of our study population received regular
drug abuse treatment.

Engaging illicit drug abusers in treatment for at least 6 months has
been associated with significant improvement in both health and social
indicators such as keeping outpatient appointments and improving
housing situations.27 A reduction in hospitalization of HIV-positive
and HIV-negative patients has been associated with participation in
methadone treatment at 1 institution.28

Regardless of HIV status, we observed at least a one-quarter reduction
in the adjusted odds of any hospitalization in 1997 associated with
receipt of both regular medical care and regular drug abuse care in
1996. While the strongest protective association in the HIV-positive
group was observed for persons with both forms of care, HIV-negative
drug users with drug abuse treatment alone showed an equally favorable
association with lower hospitalization rates.

These data support the benefits of linking persons who abuse illicit
drugs to these 2 complementary types of ambulatory care to reduce
subsequent use of inpatient care. However, the observational nature of
this study prohibits conclusions about causal relationships. Although
our models adjusted for several demographic characteristics associated
with entry and retention in substance abuse treatment,29, 30 other
factors such as history of a criminal record and drug use during
treatment29 were unavailable for this claims-based analysis.

Following the recommendations of D'Agostino,25 we used propensity
score methods to reduce potential selection bias by categorizing
patients into quintiles of similar risk of having specific patterns of
care. Models including propensity scores showed little change in the
adjusted odds of hospitalization for persons with both regular medical
and regular drug abuse care. Furthermore, our adjusted analyses
included as a potential confounder an indicator for each patient's
total hospital days during the baseline year. Among HIV-negative
persons, Neimcryk and colleagues31 demonstrated that previous
hospitalization predicts future hospitalization. In that study, 58% of
persons hospitalized in the baseline time period had another
hospitalization in a subsequent time period. By including this
variable as a covariate, we biased our analysis against finding an
effect related to care type. We believe that these results are
sufficiently robust to support approaches to promote continuity of
medical and drug abuse treatment in drug users.

Regular drug abuse care alone or with regular medical care was most
strongly associated with lower likelihood of hospitalization for
alcohol-or mental health?related complications. As expected,
hospitalization for medical complications such as pneumonia was less
likely for persons with medical care alone whether or not they also
had regular drug abuse care. However, receipt of regular medical care
and/or regular drug abuse care showed a less favorable effect on the
probability of subsequent hospitalization for drug abuse?related
diagnoses. Stein1 reported that most hospitalizations for a sample of
HIV-positive persons without AIDS were for users of injected drugs
with drug abuse?related complications. Since drug users in treatment
often persist in using illicit drugs, albeit often at reduced levels,
it is possible that drug abuse?related conditions that warrant
hospitalization may be more likely to be detected while in drug
treatment, leading to greater inpatient care. When we excluded
hospitalizations for detoxification, regular medical and regular drug
abuse care were associated with significantly lower adjusted odds of
drug abuse?related hospitalization. The role of inpatient
detoxification is controversial and considered by some as not
warranting inpatient care.32 Nonetheless, these additional analyses
suggest that a substantial proportion of the drug use?related
hospitalizations might have been for detoxification.

Our claims-based analysis also did not distinguish specific services
delivered at the drug abuse treatment sites or whether medical care
services were available on site. Samet and colleagues33 postulated
that important benefits would accrue from linking drug abuse care to
medical care in the same setting.

New York State has fostered co-located medical care for HIV-positive
drug users in drug abuse treatment, which may explain the higher
proportion of these patients with both forms of care than among
HIV-negative drug users.

Others have found that on-site medical services have several effects
for HIV-positive patients.34, 35 For other diseases such as
tuberculosis, medical care linked to drug abuse treatment appears to
be cost effective.36 To improve the likelihood that drug users receive
both forms of care, the linked-care model should be explored for both
HIV-positive and HIV-negative persons on a broader scale.

Specific characteristics of medical care settings may also influence
the probability of hospitalization. For HIV-positive drug users with a
clinic as their usual source of medical care, we have shown previously
that the adjusted odds of hospitalization were at least 50% lower for
patients in clinics with case managers or with a high degree of
coordination of care according to the clinic director.37 To reduce
hospitalization of drug users, additional studies should assess
alternative drug abuse treatment models ranging from the most basic
(eg, striving to retain drug users in drug treatment and in medical
care) to more specific efforts (eg, offering targeted services in
these settings).

Our study years witnessed the introduction of highly active
antiretroviral therapy (HAART) that can reduce the need for inpatient
care of HIV-positive persons.38 We did not consider the use of HAART
in this analysis of both HIV-positive and HIV-negative drug users but
expect that improved access to these medications may contribute to the
benefit associated with regular medical care for HIV-positive persons.
In a sample of nearly 300 HIV-positive women in their first year
postpartum (of whom 29% had evidence of current drug abuse), we found
that visits to NYS medical providers offering an array of HIV-specific
services were associated with increased adjusted odds of
antiretroviral therapy treatment and adherence.39

Several other limitations of our study deserve mention.

We used claims data to identify our study population. Yet, our
validation study suggests that our algorithms performed well in
identifying drug users and persons with HIV infection.

We did not specifically investigate the impact of mental health and
alcohol treatment, but focused more narrowly on the relationship of
medical and drug abuse care and hospitalization. Use of psychiatric
and alcohol abuse services may further contribute to variation in
hospitalization.40

The study's strengths are its large population-based sample and
empirically defined patterns of care. Our data offer compelling
evidence of an association between drug users' outpatient care
patterns and future hospitalization. Efforts to promote access to and
retention in medical care and drug abuse treatment appear to be an
attractive strategy for improving the health of this medically complex
population.

Author/Article Information

Author Affiliations: Division of Internal Medicine (Dr Laine), Center
for Research in Medical Education and Health Care (Dr Laine), and
Division of Clinical Pharmacology (Dr Hauck), Jefferson Medical College,
Thomas Jefferson University, Philadelphia, Pa; AIDS Institute, New York
State Department of Health, Albany (Mr Rothman); Division of General
Internal Medicine, University of Pennsylvania School of Medicine,
Philadelphia, Pa (Drs Cohen and Turner); Division of Substance Abuse,
Department of Psychiatry and Behavioral Sciences, Montefiore Medical
Center/Albert Einstein College of Medicine, Bronx, NY (Dr Gourevitch).

Corresponding Author and Reprints: Barbara J. Turner, MD, MSEd, Division
of General Internal Medicine, University of Pennsylvania, 1122 Blockley
Hall/6021, 423 Guardian Dr, Philadelphia, PA 19104 (e-mail:
bturner@mail.med.upenn.edu).

Author Contributions: Study concept and design: Laine, Hauck,
Gourevitch, Rothman, Turner.

Acquisition of data: Laine, Turner.

Analysis and interpretation of data: Laine, Hauck, Gourevitch,
Rothman, Cohen, Turner.

Drafting of the manuscript: Laine, Turner.

Critical revision of the manuscript for important intellectual
content: Laine, Hauck, Gourevitch, Rothman, Cohen, Turner.

Statistical expertise: Laine, Hauck, Cohen, Turner.

Obtained funding: Laine, Hauck, Turner.

Administrative, technical, or material support: Gourevitch, Rothman,
Cohen, Turner.

Study supervision: Turner.

Funding/Support: This work was supported by the National Institute on
Drug Abuse (R01 DA11606), which had no role in the design or conduct of
the study or in the reporting of results.

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