HOSPITAL UTILIZATION AND COSTS IN A COHORT OF INJECTION DRUG USERS

Abstract

Background:

Many injection drug users (IDUs) seek care at emergency departments
and some require hospital admission because of late presentation in
the course of their illness. We determined the predictors of frequent
emergency department visits and hospital admissions among
community-based IDUs and estimated the incremental hospital
utilization costs incurred by IDUs with early HIV infection relative
to costs incurred by HIV-negative IDUs.

Methods:

The Vancouver Injection Drug User Study (VIDUS) is a prospective
cohort study involving IDUs that began in 1996. Our analyses were
restricted to the 598 participants who gave informed consent for our
study. We used the participants' responses to the baseline VIDUS
questionnaire and, from medical records at St. Paul's Hospital,
Vancouver, we collected detailed information about the frequency of
emergency department visits, hospital admissions and the primary
diagnosis for all visits or hospital stays between May 1, 1996, and
Aug. 31, 1999. The incremental difference in hospital utilization
costs by HIV status was estimated, based on 105 admissions in a
subgroup of 64 participants.

Results:

A total of 440 (73.6%) of the 598 IDUs made 2763 visits to the
emergency department at St. Paul's Hospital during the study period.
Of these 440, 265 (60.2%) made frequent visits (3 or more). The
following factors were associated with frequent use: HIV-positive
status (seroprevalent: adjusted odds ratio [OR] 1.7, 95% confidence
interval [CI] 1.2-2.6; seroconverted during study period: adjusted OR
3.0, 95% CI 1.6-5.7); more than 4 injections daily (adjusted OR 1.5,
95% CI 1.1-2.1); cocaine use more frequent than use of other drugs
(adjusted OR 2.0, 95% CI 1.2-3.6); and unstable housing (adjusted OR
1.5, 95% CI 1.1-2.2). During the study period 210 of the participants
were admitted to hospital 495 times; 118 (56.2%) of them were admitted
frequently (2 or more admissions). The 2 most common reasons for
admission were pneumonia (132 admissions among 79 patients) and
soft-tissue infections (cellulitis and skin abscess) (90 admissions
among 59 patients). The following factors were independently
associated with frequent hospital admissions: HIV-positive status
(seroprevalent: adjusted OR 5.4, 95% CI 3.4-8.6; seroconverted during
study period: adjusted OR 2.9, 95% CI 1.4-6.0); and female sex
(adjusted OR 1.8, 95% CI 1.1-3.1). The incremental hospital
utilization costs incurred by HIV-positive IDUs relative to the costs
incurred by HIV-negative IDUs were $1752 per year.

Interpretation:

Hospital utilization was significantly higher among community-based
IDUs with early HIV disease than among those who were HIV negative.
Much of the hospital use was related to complications of injection
drug use and may be reduced with the establishment of programs that
integrate harm reduction strategies with primary care and addiction
treatment.

Many injection drug users (IDUs) use emergency departments as a
regular source of care because of the lack of accessible primary care
services or their inability to attend set appointment times. [1,2,3,4]
Poor health status among IDUs because of drug use, HIV infection or
hepatitis C is common, and some IDUs present later in the course of an
illness and thus require hospital admission. [4,5,6,7,8] IDUs at all
stages of HIV infection are admitted to hospital significantly more
often than non-IDUs with HIV infection. [9]

Because hospital admissions among HIV-positive IDUs are largely
attributable to complications of injection drug use [10] that are not
directly related to the HIV infection, it is unclear whether
community-based HIV-negative IDUs have similar hospital utilization
patterns as IDUs with early HIV disease. Other studies of health care
use by IDUs have been in the setting of drug treatment or clinics and
reflect a highly selected population. [11,12] We therefore conducted
this study to determine the predictors of frequent emergency
department use among community-based IDUs. We also examined the
predictors of frequent hospital admission and reviewed the primary
diagnosis for each encounter. To assess whether there was a difference
in hospital utilization costs according to HIV status, we estimated
the incremental costs incurred by IDUs with early stage disease
relative to costs incurred by HIV-negative IDUs. With the rising
prevalence of HIV infection among IDUs in many Canadian cities,
including Vancouver, [13,14] these data may be crucial for planning
and evaluating programs that provide appropriate health care services
to reduce drug-related harm among active IDUs with or at risk of HIV
infection.

Methods

We obtained informed consent from 598 participants of the Vancouver
Injection Drug User Study (VIDUS) to review their medical records at
St. Paul's Hospital, the main teaching hospital for IDUs and HIV care
in Vancouver. The hospital's Committee on Human Experimentation
approved the study. The research design and methods of the VIDUS have
been previously described; [13] the primary aim was to determine the
risk practices associated with HIV seroconversion. In brief, subjects
were eligible to participate in the VIDUS if they had injected illicit
drugs in the month before enrolment and resided in the Greater
Vancouver region. Most participants (82%) were recruited through word
of mouth and street outreach programs. Participants provided blood
samples for HIV antibody testing and responded to an
interviewer-administered questionnaire semi-annually. Responses from
the baseline survey were used for our analyses. We reviewed medical
records from St. Paul's Hospital for the 598 participants to determine
the frequency of emergency department use and hospital admissions as
well as the presenting problem for each emergency department visit and
the primary diagnosis for each hospital admission between May 1, 1996,
and Aug. 31, 1999.

Hospital utilization costs were estimated according to the inpatient
resource-utilization profiles of a random sample of 64 participants
who were admitted to hospital during the study period. Our cost
estimates were for the first 105 admissions. For each admission,
information was abstracted from the medical records, including the
nursing ward, medications received, investigations, physicians' visits
and length of stay. To distinguish between costs and charges, [15] we
estimated inpatient unit costs using a model of simultaneous
allocation [16] of all expenditures including overhead, opportunity
cost of hospital resources as well as a 5% global depreciation of
capital equipment.

Contingency tables were used to examine associations between frequent
users and nonfrequent users of the emergency department and hospital
by their HIV status and other sociodemographic and behavioural
characteristics. We defined a priori frequent emergency department use
as 3 or more visits and frequent hospital admission as 2 or more stays
during the study period. We classified HIV status as seroprevalent (n
= 166), seroconverted (for HIV seroconversions that occurred during
the study period) (n = 51) and negative (n = 381). Unstable housing
was defined as living in a single-occupancy room hotel, boarding room,
hostel, transition house, jail or on the street in the 6 months before
enrolment in the study. [3,13] The Wilcoxon rank-sum test was used to
compare continuous variables.

To identify independent predictors of frequent emergency department
use, variables significant at the 0.05 level in the univariate
analysis were entered into logistic regression models in a stepwise,
hierarchical fashion. In the final model, all relevant 2-way
interactions were considered. This procedure was also performed to
identify predictors of frequent hospital admission. We also compared
self-reported hospital admissions in the 6 months before entry into
the study and at follow-up (1999) by HIV status to assess the extent
to which HIV-negative IDUs could have been admitted to hospital elsewhere.

To estimate the incremental difference in hospital utilization costs
between IDUs with early HIV infection and HIV-negative IDUs, the
average daily cost was multiplied by the median length of stay and
then the annualized frequency of hospital admission per person by HIV
status. [17] We performed 2-way sensitivity analyses using the lower
and upper limits of the 95% confidence interval (CI) for the hospital
utilization costs and simultaneously varying the length of stay by
calculating the difference in length of stay by HIV status using the
25th and 75th percentiles.

Results

Hospital Utilization

Of the 598 participants included in our analysis, 440 (73.6%) of them
visited the emergency department a total of 2763 times during the
39-month study period. Of these 440 IDUs, 265 (60.2%) visited the
emergency department frequently and 91 (20.7%) visited more than 10
times. The annualized frequency of emergency department use by HIV
status was 2.6 for the IDUs with seroprevalent HIV infection (1171
visits among 137 patients), 2.9 for the IDUs with seroconverted HIV
infection (387 visits among 41 patients) and 1.4 for the HIV-negative
IDUs (1205 among 262 patients). The 2 most common reasons for visiting
the emergency department were soft-tissue infections (cellulitis and
skin abscess) and problems directly related to illicit drug use (e.g.,
drug intoxication, overdose and drug withdrawal)

Overall, 210 (35.1%) of the 598 participants were admitted to the
hospital 495 times during the study period. Of these 210, 118 (56.2%)
were admitted frequently and 21 (10.0%) had 5 or more admissions. The
annualized frequency of hospital admissions by HIV status was 0.89 for
the IDUs with seroprevalent HIV infection (294 admissions among 102
patients), 0.80 for the IDUs with seroconverted HIV infection (52
admissions among 20 patients) and 0.52 for the HIV-negative IDUs (149
admissions among 88 patients). The 2 most common reasons for admission
were pneumonia (132 admissions among 79 patients) and soft-tissue
infections (cellulitis and skin abscess, 90 admissions among 59
patients) (Table 1). The HIV-negative IDUs were less likely than the
HIV-positive IDUs to report hospital admissions in the 6 months before
entry into the study (odds ratio [OR] 0.43, 95% CI 0.29-0.67) and in
the 6 months before follow-up (OR 0.48, 95% CI 0.29-0.77).

The crude and adjusted ORs for the predictors of frequent emergency
department use and frequent hospital admission are shown in Table 2
and Table 3 respectively. Logistic regression analysis showed that
frequent emergency department use was associated with HIV infection
(seroprevalent: adjusted OR 1.7, 95% CI 1.2-2.6; seroconverted:
adjusted OR 3.0, 95% CI 1.6-5.7), injection more than 4 times daily
(adjusted OR 1.5, 95% CI 1.1-2.1), cocaine use more frequent than use
of other drugs; adjusted OR 2.0, 95% CI 1.2-3.6) and unstable housing
(adjusted OR 1.5, 95% CI 1.1-2.2). The following factors were
independently associated with frequent hospital admission: HIV
infection (seroprevalent: adjusted OR 5.4, 95% CI 3.4-8.6;
seroconverted: adjusted OR 2.9, 95% CI 1.4-6.0) and female sex
(adjusted OR 1.8, 95% CI 1.1-3.1).

Utilization Costs

The 64 IDUs included in the subgroup cost analysis were admitted to
hospital 184 times during the study period. Of the 64 participants, 33
had seroprevalent HIV infection at baseline and 5 became HIV positive
during the study period, with a median CD4 count of 389 x 106/L
(interquartile range [IQR] 216-592 x 106/L) at their first hospital
admission. The 5 who became HIV positive during the study period had
not been admitted to hospital when they were HIV negative. The IDUs
who were HIV-positive had a longer length of stay (median 7 days, IQR
5-12 days) than the HIV-negative IDUs (median 5 days, IQR 4-8 days).
The annualized frequency of hospital admissions was 0.96 among the
seroprevalent HIV-positive IDUs and 0.77 among the HIV-negative IDUs.
The fully allocated average hospital utilization cost per day was
$610.33 (95% CI $575.70-$644.96). The incremental hospital utilization
cost incurred by the HIV-positive IDUs relative to the HIV-negative
IDUs was $1752 per year (the sensitivity analyses showed that the
incremental cost varied from $990 to $3457 per year).

Interpretation

We found that the HIV-positive IDUs visited the emergency department
and were admitted to hospital substantially more often than the
HIV-negative IDUs. This may have been due to continued high-risk
injection behaviours, particularly among the IDUs who became HIV
positive during the study period. Our annualized frequency of
emergency department use among the HIV-negative IDUs was higher than
the estimate reported by French and associates [4] (1.4 v. 0.78); the
same was true for the annualized frequency of hospital admissions
(0.52 v. 0.32). These differences may have been due to differences in
population, health care systems and ascertainment of health care use
(self-report versus actual).

Our finding that female sex was an independent predictor of frequent
hospital admission is consistent with previous findings. [6,18,19] The
recent HIV Costs and Services Utilization Study in the United States
reported that the suboptimal pattern of care among women and IDUs was
largely mitigated by adjusting for insurance coverage and race or
ethnic background. [20] Comparisons with US findings are difficult
given differences in the health care systems and the demographic
composition of the study populations. The association between the use
of cocaine and unstable housing with frequent emergency department use
has been noted elsewhere. [21,22,23,24]

The predominant reasons for hospital admission (pneumonia and
soft-tissue infections) in our study are directly and indirectly
related to needle use and highlight the importance of counselling and
providing the tools necessary to practise safe injection techniques.
In a study by Stein, [10] HIV-positive IDUs were admitted to an urban
hospital primarily because of injection-related complications. In
another study, involving IDUs in drug treatment, those with early HIV
infection used more ambulatory and inpatient services than
HIV-negative IDUs. [12] An increased biological susceptibility to
bacterial infections [8,25] or poor hygiene and high-risk drug
injection practices [13,26] are possible explanations for the higher
frequency of hospital admissions among HIV-positive IDUs.

Our study had several limitations. First, we may have underestimated
the emergency department and hospital use because the participants may
have received care from other hospitals. Second, we did not capture
outpatient clinic visits. Third, we used a relatively small sample of
IDUs to estimate the hospital utilization costs. Finally, the study
participants may not be representative of all IDUs, because those in
the lowest socioeconomic group may have been overrepresented in our
study population.

Our cost analysis builds on previous work in that we examined actual
hospital costs for IDUs by assigning fully allocated costs of actual
resource use. In other studies costs were derived from charge data,
[4,10,27] or aggregated service utilization costs were used to
calculate costs per patient-year. [28,29] The incremental hospital
utilization costs incurred by the HIV-positive IDUs relative to the
costs incurred by the HIV-negative IDUs were $1752 per person; this
translates into an additional $197 976 per year for hospital care for
the 113 HIV-positive IDUs who were admitted to hospital during our
study period.

A recent study reported high hospital use and costs among poor people
in Toronto. [30] Our results provide some reasons for their findings
among the IDU subgroup. Much of the health care use was largely
attributable to complications of injection drug use, regardless of HIV
status. The use of sterile injecting equipment and safe injection
practices might have prevented many of these conditions and, thus,
reduced the need for emergency department visits or hospital
admissions. [31,32] Programs that integrate harm reduction strategies
with primary care and addiction treatment [33,34] should be considered
by jurisdictions serving this vulnerable population.

Competing Interests: None declared.

Contributors: Anita Palepu was the principal author, conceived and designed
the study and was responsible for the interpretation of the data. Mark
Tyndall was responsible for the analysis and interpretation of data and for
revising the manuscript. Hector Leon was responsible for the costing of the
hospital resource use profiles and for revising the manuscript. Jennifer
Muller was responsible for data collection and linkage to the Vancouver
Injection Drug User Study survey data and for revising the manuscript.
Michael O'Shaugnessy and Martin Schechter contributed to the interpretation
of the data and revision of the manuscript. Aslam Anis contributed to the
study design, was responsible for the costing methodology and
interpretation and for revising the manuscript.

Acknowledgements: We thank Kathy Li for the statistical analyses, Laura
Kuyper for database management, the Vancouver Injection Drug User Study
(VIDUS) staff and the VIDUS Community Advisory Board.

This research was funded by the British Columbia Health Research
Foundation, the National Institutes of Health (grant R01 DA11591-01),
the British Columbia Ministry of Health and Health Canada. Anita
Palepu was supported by a National Health Research Scholar Award from
the National Health Research and Development Program of Health Canada,
and Martin Schechter was supported by a National AIDS Research
Scientist Award.

This article has been peer reviewed.

Correspondence to: Dr. Anita Palepu, Rm. 620B, St. Paul's Hospital,
1081 Burrard St., Vancouver BC V6Z 1Y6; fax 604 806-8005;
anita@hivnet.ubc.ca

References

1. Solomon L, Frank R, Vlahov D, Astemborski J. Utilization of health
services in a cohort of intravenous drug users with known HIV-1 serostatus.
Am J Public Health 1991;81:1285-90. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid'026649&Dopt=r
]

2. Markson LE, Houchens R, Fanning TR, Turner BJ. Repeated emergency
department use by HIV-infected persons: effect of clinic accessibility and
expertise in HIV care. J Acquir Immune Defic Syndr Hum Retrovirol
1998;17:35-41. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=98097256&Dopt=r
]

3. Palepu A, Strathdee SA, Hogg RS, Anis AH, Rae S, Cornelisse PG, et al.
The social determinants of emergency department and hospital use by
injection drug users in Canada. J Urban Health 1999;76:409-18. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid075682&Dopt=r
]

4. French MT, McGeary KA, Chitwood DD, McCoy CB. Chronic illicit drug use,
health services utilization and the cost of medical care. Soc Sci Med
2000;50:1703-13. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid256184&Dopt=r
]

5. Weber AE, Yip B, O'Shaughnessy MV, Montaner JS, Hogg RS. Determinants
of hospital admission among HIV-positive people in British Columbia
../../vol-162/issue-6/0783.htm . CMAJ 2000;162(6):783-6.

6. Aday L. Health status of vulnerable populations. Annu Rev Public Health
1994;15:487-509. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"331077&Dopt=r
]

7. Guydish J, Bucardo J, Clark G, Bernheim S. Evaluating needle exchange:
a description of client characteristics, health status, program
utilization, and HIV risk behavior. Subst Use Misuse 1998;33:1173-96.
[MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=98255821&Dopt=r
]

8. Stein MD. Medical complications of intravenous drug use. J Gen Intern
Med 1990;5:249-57. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=90257738&Dopt=r
]

9. Brettle RP, Willcocks L, Cowan FM, Richardson AM. Inpatient health care
utilization for patients with HIV and AIDS in the Edinburgh City Hospital.
Int J STD AIDS 1994;5:194-201. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"339223&Dopt=r
]

10. Stein MD. Injected-drug use: complications and costs in the care of
hospitalized HIV-infected patients. J Acquir Immune Defic Syndr
1994;7:469-73. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"210372&Dopt=r
]

11. Umbricht-Schneiter A, Ginn DH, Pabst KM, Bigelow GE. Providing medical
care to methadone clinic patients: referral versus on-site care. Am J
Public Health 1994;84:207-10. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"127627&Dopt=r
]

12. Stein MD, O'Sullivan PS, Ellis P, Perrin H, Wartenberg A. Utilization
of medical services by drug abusers in detoxification. J Subst Abuse
1993;5:187-93. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"003984&Dopt=r
]

13. Strathdee SA, Patrick DM, Currie SL, Cornelisse PG, Rekart ML,
Montaner JS, et al. Needle exchange is not enough: lessons from the
Vancouver injecting drug use study. AIDS 1997;11:F59-65. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid--366914&Dopt=r
]

14. Patrick DM, Strathdee SA, Archibald CP, Ofner M, Craib KJ, Cornelisse
PG, et al. Determinants of HIV seroconversion in injection drug users
during a period of rising prevalence in Vancouver. Int J STD AIDS
1997;8:437-45. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid--372351&Dopt=r
]

15. Finkler SA. The distinction between cost and charges. Ann Intern Med
1982;96:102-9. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=82089562&Dopt=r
]

16. Drummond M. Methods for the evaluation of health care programmes.
Oxford: Oxford University Press; 1996.

17. Anis AH, Hogg RS, Wang XH, Yip B, Palepu A, Montaner JS, et al.
Modelling the potential economic impact of viral load-driven triple drug
combination antiretroviral therapy. Pharmacoeconomics 1998;13:697-705.
[MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=98280305&Dopt=r
]

18. Solomon L, Stein M, Flynn C, Schuman P, Schoenbaum E, Moore J, et al.
Health services use by urban women with or at risk for HIV-1 infection: the
HIV Epidemiology Research Study (HERS). J Acquir Immune Defic Syndr Hum
Retrovirol 1998;17:253-61. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=98154614&Dopt=r
]

19. Hulka B, Wheat J. Patterns of utilization: the patient perspective.
Med Care 1985;23:438-60. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=85239174&Dopt=r
]

20. Shapiro MF, Morton SC, McCaffrey DF, Senterfitt JW, Fleishman JA,
Perlman JF, et al. Variations in the care of HIV-infected adults in the
United States: results from the HIV Cost and Services Utilization Study.
JAMA 1999;281:2305-15. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=99313126&Dopt=r
]

21. Padgett DK, Struening EL. Influence of substance abuse and mental
disorders on emergency room use by homeless adults. Hosp Community
Psychiatry 1991;42:834-8. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid'372799&Dopt=r
]

22. Bangsberg D, Tulsky JP, Hecht FM, Moss AR. Protease inhibitors in the
homeless. JAMA 1997;278:63-5. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid--350965&Dopt=r
]

23. Smith MY, Rapkin BD, Winkel G, Springer C, Chabra R, Feldman IS.
Housing status and health care service utilization among low-income persons
with HIV/AIDS. J Gen Intern Med 2000;15:731-8. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid539449&Dopt=r
]

24. Kushel MB, Vittinghoff E, Haas JS. Factors associated with the health
care utilization of homeless persons. JAMA 2001;285:200-6. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=21105380&Dopt=r
]

25. Selwyn PA, Alcabes P, Hartel D, Buono D, Schoenbaum EE, Klein RS, et
al. Clinical manifestations and predictors of disease progression in drug
users with human immunodeficiency virus infection. N Engl J Med
1992;327:1697-703. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"063108&Dopt=r
]

26. Archibald CP, Ofner M, Strathdee SA, Patrick DM, Sutherland D, Rekart
ML, et al. Factors associated with frequent needle exchange program
attendance in injection drug users in Vancouver, Canada. J Acquir Immune
Defic Syndr Hum Retrovirol 1998;17:160-6. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=98132360&Dopt=r
]

27. Bentham WD, Cai L, Schulman KA. Characteristics of hospitalizations of
HIV-infected patients: an analysis of data from the 1994 healthcare cost
and utilization project. J Acquir Immune Defic Syndr 1999;22(5):503-8.
[MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid415786&Dopt=r
]

28. Beck EJ, Whitaker L, Kennelly J, McKevitt C, Wadsworth J, Miller DL,
et al. Changing presentation and survival, service utilization and costs
for AIDS patients: insights from a London referral centre. AIDS
1994;8:379-84. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"304560&Dopt=r
]

29. Beck EJ, Kennelly J, McKevitt C, Whitaker L, Wadsworth J, Miller DL,
et al. Changing use of hospital services and costs at a London AIDS
referral centre, 1983-1989. AIDS 1994;8:367-77. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"304559&Dopt=r
]

30. Glazier RH, Badley EM, Gilbert JE, Rothman L. The nature of increased
hospital use in poor neighbourhoods: findings from a Canadian inner city.
Can J Public Health 2000;91:268-73. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid442852&Dopt=r
]

31. Vlahov D, Sullivan M, Astemborski J, Nelson KE. Bacterial infections
and skin cleaning prior to injection among intravenous drug users. Public
Health Rep 1992;107:595-8. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid"029205&Dopt=r
]

32. Van Haastrecht HJ, Bindels PJ, Sluijs TA, Van den Hoek AA, Reijneveld
SA, Coutinho RA. The impact of drug users on inpatient hospital care during
the human immunodeficiency virus epidemic in Amsterdam. Int J Epidemiol
1996;25:846-53. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid--079755&Dopt=r
]

33. McGeary KA, French MT. Illicit drug use and emergency room
utilization. Health Serv Res 2000;35:153-69. [MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid239099&Dopt=r
]

34. Laine C, Hauck WW, Gourevitch MN, Rothman J, Cohen C, Turner BJ.
Regular outpatient medical and drug abuse care and subsequent
hospitalization of persons who use illicit drugs. JAMA 2001;285:2355-62.
[MEDLINE
http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m&form=6&uid=21242940&Dopt=r