Regional and temporal trends in migration among people living with HIV/AIDS in British Columbia, 1993-2005.

Lima, Viviane D. ; Druyts, Eric ; Montaner, Julio S.G. 等

It was estimated that 12,300 individuals were living with HIV in British Columbia (BC) in 2005, representing 21% of all prevalent HIV cases in Canada, next only to Ontario (48%) and Quebec (28%). (1-4) In BC, new HIV infections were historically observed in gay and bisexual men, most residing in Vancouver. Specialized HIV-related services have therefore been centralized in Vancouver. (5) However, over time an increasing number of new infections have been observed in other subpopulations, such as disadvantaged individuals and visible minorities, some of whom reside outside Vancouver. (6)

Two earlier studies indicate that when antiretroviral therapy became widely available throughout the province in the early to mid-1990s, a large number of people migrated to Vancouver from other parts of the province. (7,8) This was believed to be driven by the availability of specialized HIV-related services in Vancouver. (9) Therefore, moving to Vancouver was seen as a way to alleviate problems related to the geographical accessibility of services. However, despite a universal health care system where medically necessary services and antiretroviral therapy are provided free of charge to clinically eligible people with HIV, it is estimated that only 50% of the eligible HIV-positive individuals in BC are currently accessing therapy. (10)

The purpose of this study was to examine regional and temporal trends in migration among patients receiving antiretroviral therapy for the treatment of HIV in BC. Analyses were stratified by regional health authority and local health areas during 1993-2005.

Estimates of migration between and within regions over time can provide useful information for health planners and policy-makers to make informed decisions regarding the allocation of services for those in medical need.

METHODS

Study population

Data for this study were drawn from the BC Centre for Excellence in HIV/AIDS Drug Treatment Program (DTP). The DTP has a provincial mandate to distribute antiretroviral therapy at no cost to all clinically eligible HIV-positive patients in BC. (11,12) The guidelines for clinical eligibility of antiretroviral therapy are consistent with those published by the International AIDS Society-USA. The DTP administrative database includes information on patients' residential address, history of antiretroviral medication, markers of HIV disease progression (i.e., HIV viral load, CD4 cell count, antiretroviral resistance), mortality, and co-morbidities, among other clinically relevant factors. Typically, patients on antiretroviral therapy are monitored by physicians at intervals no longer than three months, at which time prescriptions are renewed or modified and patients' addresses are updated in the DTP database. Since 1992, the DTP has provided treatment to over 9,000 individuals in BC. (12)

The data used in this study were a subset of the DTP, and include administrative records of patients >18 years of age who started antiretroviral therapy between January 1, 1993 and November 30, 2004, and followed until death, the last contact date, or the end of study follow-up (November 30, 2005). This analysis has received ethical approval from the University of British Columbia/ Providence Health Care Research Ethics Board.

Regional health boundaries in BC

Our analyses were conducted using the following geographical boundaries defined by the BC Ministry of Health: 89 local health areas (LHA) nested within 16 health services delivery areas (HSDA), within 5 health authorities (HA). (13) The 5 HAs--Interior, Fraser, Vancouver Coastal, Vancouver Island and Northern--are responsible for the management and delivery of health services in geographically defined subpopulations in BC. The 89 LHAs are used predominantly for data-disseminating purposes within each HSDA. The HSDAs are responsible for managing the delivery of health services in their respective areas, and meeting performance objectives set by HAs. The LHAs and HAs were used to define place of residence of the patients in this study. The map of BC stratified by HSDA and HA, with their respective names, is presented in Figure 1.

Migration indicators and analyses

We define migration (or internal migration) as the movement from one LHA (or HA) to another. This movement can be temporary or permanent and may be for voluntary or involuntary reasons. (14) A number of population and migration indicators were used to study the migration trends across the HAs during 1993-2005. (14,15) First, we assessed internal migration of different HAs by comparing the last recorded HA of residence to the first recorded HA of residence for each patient. Second, we calculated three common migration rates for each HA defined as:

* In-migration rate: ([I.sub.HA.sub.[i]]/[P.sub.HA.sub.[i]]) x 1000, where [I.sub.HA.sub.[i]] is the number of in migrants during a specified time for the [i.sup.th] HA (i = Interior, Fraser, Vancouver Coastal, Vancouver Island and Northern); and [P.sub.HA.sub.[i]] is the population of the [i.sup.th] HA at the mid-point of the migration interval.

* Out-migration rate: ([O.sub.HA.sub.[i]]/[P.sub.HA.sub.[i]]) x 1000, where [O.sub.HA.sub.[i]] is the number of outmigrants during a specified time for the [i.sup.th] HA (i = Interior, Fraser, Vancouver Coastal, Vancouver Island and Northern); and [P.sub.HA.sub.[i]] is defined above.

* Net-migration rate: (([I.sub.HA.sub.[i]]-[O.sub.HA.sub.[i])/[P.sub.HA.sub.[i]]) x 1000, where [I.sub.HA.sub.[i]], [O.sub.HA.sub.[i]] and [P.sub.HA.sub.[i]] are defined above.

Third, we calculated three measures of population distribution. The first two measures examine the degree of non-uniformity in the distribution of the patients' residence across the HAs; they are called the concentration ratio and the index of concentration. They both measure the degree of variability of the population distribution at a given point in time. They can also be interpreted as the percentage of HIV-infected patients who would need to move locations so that an even distribution of HIV-positive individuals is obtained among the different HAs. These indexes usually give very similar results, however the index of concentration is less computationally intensive. The third measure is called the index of dissimilarity, and it measures the change in the degree of variability in a given area between two points in time. In our database, it was possible to account for all migration movements, provided the participant communicated a change in address when they refilled their prescriptions. Therefore, a patient can move more than one time during a particular era, or even during a particular year, and the data were built to account for all such movements. Thus, we calculated these measures comparing different milestone years in our drug treatment program: 1993 (pre-highly active antiretroviral therapy (HAART)) & 1996 (first time HAART became available containing non-boosted protease inhibitors), 1996 & 1999 (when HAART containing nonnucleoside reverse transcriptase inhibitors became available), 1996 & 2001 (when boosted protease inhibitors [more potent than the unboosted version of this drug] became available), 1996 & 2003 (newer drug combinations introduced to patients in our Centre) and 1996 & 2005 (the latest drug combinations available to our patients).

[FIGURE 1 OMITTED]

We also used mapping to contrast low and high disease risk areas, identify geographical clusters of disease incidence, and provide etiological clues based on the distribution of disease risk. (16) Crude migration rates at the LHA level were mapped over time to show the spatial distribution of place of residence of patients. We calculated these crude rates using non-overlapping time intervals, defined by the periods 1993-1996, 1997-1999, 2000-2002, and 2003-2005. To calculate the migration rates over time, we used the annual BC population size estimates for 1993-2005 as a denominator. (17) These population estimates represent individuals aged 1564 years and are specific to each HA and LHA. Analyses were conducted using SAS version 9.1.3 (SAS, Cary, NC) and ArcView version 9 (ESRI, Redlands, CA).

RESULTS

A total of 3,588 patients enrolled in the DTP were followed between January 1, 1993 and November 30, 2005, translating into a median follow-up time of 3.9 years (interquartile range: 1.8-6.7 years). At the end of follow-up, 19.3% of patients died of non-AIDS or AIDS-related causes (rate 44.8 per 1000 person-years), 7.9% were lost to follow-up (rate 18.3 per 1000 person-years), 3.5% moved out of BC (rate 8.1 per 1000 person-years), 2.3% were censored because they had enrolled in a blinded trial involving receiving placebo medication, and 67.0% were followed until the study ending date (rate 155.1 per 1000 person-years).

Table 1 displays the results of the different migration and population indicators. Table 1(a) shows the distribution of the patient's initial residence recorded at the beginning of the study period by their last residence recorded. We observed that for all HAs except Vancouver Coastal, about half of the patients did not migrate during the study period, or if they did, they returned to their first residence recorded by the end of the study (Interior: 47%, Fraser: 50%, Vancouver Island: 60%, and Northern: 48%). Most patients living in Vancouver Coastal remained in this region during this period, or at least had the same first and last residences during the study period (81%). Patients who migrated most often migrated to the Vancouver Coastal HA (from the Interior: 30%, Fraser: 41%, Vancouver Island: 28%, and Northern: 19%). Consequently, we obtained negative net-migration rates of -240.0, -150.0, and -32.3 per 1000 population for the Interior, Vancouver Island, and Northern HAs, respectively, indicating that patients were leaving these HAs at a higher rate than entering them. Vancouver Coastal HA had a net-migration rate of 40.7 per 1000 population. What is perhaps more interesting is that the Fraser HA also had a positive net migration rate (8.2%), with most of these patients coming from the Vancouver Coastal HA.

The maps in Figure 2 illustrate the distribution of patients' place of residence while on treatment, for every 10,000 population by LHA. In the pre-HAART period (panel A), most patients were living in areas around the large cities in BC: Vancouver (Vancouver Coastal), Victoria (Vancouver Island), Prince George (Northern), Penticton, Vernon, Central Okanagan and Kamloops (Interior), and Surrey, Coquitlam, and Burnaby (Fraser). When HAART first became available (panel B), there was a high migration from remote areas to these large population centres, especially those close to Vancouver. This pattern became more evident as we approached the year 2005 (panels B-D).

Figure 3 shows the distribution of patients' place of residence from 1993 to 2005. No obvious trends were observed in Northern, Vancouver Island or Interior. As expected, the majority of patients are receiving treatment in Vancouver Coastal (p<0.01). Note that the percentage of patients residing in Fraser, while fluctuating, has been increasing since 1998 with an approximate increase of 46% in the average number of patients treated during 1993-1997 as opposed to 1998-2005 (p<0.01).

The concentration ratio, index of concentration and index of dissimilarity between different periods of time are shown in Table 1(b). These population indicators have changed significantly over time, showing that in more recent years, when compared to the first time HAART became available (1996), the heterogeneity in the distribution of the population across health regions in BC has increased over time.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

DISCUSSION

The results of this study demonstrated that Vancouver Coastal, specifically the LHAs representing Vancouver, has attracted the majority of migrant patients with HIV since the early stages of the epidemic in BC. This area attracted patients from all other regions in BC and this movement intensified over time. We also demonstrated that more patients are either migrating to Fraser (hosting the second largest centre for treatment in BC)--most likely from Vancouver Coastal--or deciding to stay in Fraser.

The results are comparable to those of other studies, where people with HIV are highly likely to move between communities and regions. (8,18-22) Reasons for migration may range from the desire to be near caregivers, specialized care, and better access to health care services, to being in communities with members of similar social interests or close to family or friends. Therefore, with inadequate health care planning, migration can impose a tremendous burden on health care systems of larger communities/cities not prepared to accommodate these extra patients. Future analysis should focus on understanding the reasons for migration of HIV patients in BC.

There are several features of this study that should be highlighted. First, this study was based on a large sample of patients within a province-wide treatment program, in which all patients had free access to medical attention, combination antiretroviral therapy, and laboratory monitoring. We are confident, therefore, that our results were not seriously influenced by inadequate sample size. Second, delayed reporting of deaths was not likely a factor since most deaths were reported within three months through active follow-up with physicians and regular linkages to the BC Vital Statistics Agency. Third, in this group of patients, given that 19.3% of patients died and 13.7% of patients were censored and not followed until the end of the study, our migration rates and indicators may have been underestimated. Finally, it is likely that over time, patients might be treated by more experienced physicians and therefore be more likely to migrate. (9,22)

Our results demonstrate that migration among patients receiving antiretroviral therapy in BC is not homogeneous, with areas around large urban centres having the highest influx of patients. It is thus important that health authorities in BC work in partnership to monitor and evaluate accessibility of HIV-related health care services to ensure universal access for all patients. Furthermore, enhanced HIV care and support services need to be developed, on a province-wide basis, and funding allocation needs to be adjusted to reflect patient migration in BC.

Acknowledgements: We thank Christopher Au-Yeung, Benita Yip, Marnie Gidman, Elizabeth Ferris, Nada Gataric, Kelly Hsu, Myrna Reginaldo, and Peter Vann for their assistance.

Conflict of Interests: Drs. Hogg and Montaner have received honoraria, travel grants to attend conferences and research grants from pharmaceutical companies working in the area of HIV/AIDS. Dr. Lima and Mr. Druyts declare no conflict.

Received: June 11, 2009 Accepted: October 8, 2009

REFERENCES

(1.) Public Health Agency of Canada. HIV and AIDS in Canada. Surveillance Report to June 30, 2006. Surveillance and Risk Assessment Division, Centre for Infectious Disease Prevention and Control, Public Health Agency of Canada, 2006.

(2.) Statistics Canada. Estimates of population, by age group and sex, Canada, provinces and territories, annual. CANSIM Table 051-0001. Available at: http://www40.statcan.ca/l01/cst01/demo02a.htm (Accessed January 29, 2009).

(3.) Bitera R, Alary M, Fauvel M, Parent R; Institut national de sante publique du Quebec. Programme de surveillance de l'infection par le virus de l'immunodeficience humaine (VIH) au Quebec--Mise a jour des donnees au 30 juin 2008. Available at: http://www.inspq.qc.ca/pdf/publications/895_SurvVIH.pdf (Accessed September 2, 2009).

(4.) Remis RS, Swantee C, Schiedel L, Lui J. Report on HIV/AIDS in Ontario 2006. Ontario Ministry of Health and Long-Term Care, March 2008. Available at: http://www.phs.utoronto.ca/ohemu/doc/PHERO2006_report_final.pdf (Accessed September 2, 2009).

(5.) Wood E, Low-Beer S, Bartholomew K, Landolt M, Oram D, O'Shaughnessy MV, et al. Modern antiretroviral therapy improves life expectancy of gay and bisexual males in Vancouver's West End. Can J Public Health 2000;91(2):125 28.

(6.) British Columbia Centre for Disease Control. STI/HIV Prevention and Control. HIV/AIDS Annual Report 2007. Available at: http://www.bccdc.org/downloads/pdf/std/reports/HIV-AIDS %20Update%20Report_2007.pdf (Accessed March 11, 2009).

(7.) Hogg RS, Schechter MT, Schilder A, Le R, Strathdee SA, Goldstone IL, et al. Access to health care and geographic mobility of HIV/AIDS patients. AIDS Patient Care 1995;9(6):297-302.

(8.) Hogg RS, Whitehead J, Ricketts M, Heath KV, Ng E, Lalonde P, et al. Patterns of geographic mobility of persons with AIDS in Canada from time of AIDS index diagnosis to death. Clin Invest Med 1997;20(2):77-83.

(9.) Heath KV, Bally G, Yip B, O'Shaughnessy MV, Hogg RS. HIV/AIDS care giving physicians: Their experience and practice patterns. Int J STD AIDS 1997;8(9):570-75.

(10.) Lima VD, Johnston K, Hogg RS, Levy AR, Harrigan PR, Montaner JSG. Expanded access to highly active antiretroviral therapy: A potentially powerful strategy to curb the growth of the HIV epidemic. J Infect Dis 2008;198(1):59-67.

(11.) Lima VD, Hogg RS, Harrigan PR, Moore D, Yip B, Wood E, et al. Continued improvement in survival among HIV infected individuals following initiation of triple and boosted combination antiretroviral regimens. AIDS 2007;21(6):685-92.

(12.) British Columbia Centre for Excellence in HIV/AIDS. Therapeutic Guidelines. 2006. Available at http://www.cfenet.ubc.ca/content.php?id=12 (Accessed November 15, 2008).

(13.) British Columbia Ministry of Health Services. Health Authorities. Roles and Responsibilities of Health Authorities. Available at http://www.healthservices.gov.bc.ca/socsec/roles.html. (Accessed December 15, 2008).

(14.) Shryock H, Siegel J. The Methods and Materials of Demography. Washington, DC: U.S. Department of Commerce, Bureau of Census, 1980.

(15.) Kpedekpo GMK. Essentials of Demographic Analysis for Africa. London, UK: Heinemann, 1982.

(16.) Lima VD. Small-Area Disability-Adjusted Life Years: A New Approach to the Spatio-Temporal Analysis of Public Health Surveillance Data. Doctoral Thesis Monograph. University of British Columbia, 2005.

(17.) BC Stats, BC Ministry of Labour and Citizens' Services, Government of British Columbia. Population Estimates and Projections (P.E.O.P.L.E. 31) by Standard Age Groups. Available at http://www.bcstats.gov.bc.ca/ data/pop/pop/estspop.asp (Accessed September 10, 2008).

(18.) Agee BS, Funkhouser E, Roseman JM, Fawal H, Holmberg SD, Vermund SH. Migration patterns following HIV diagnosis among adults residing in the nonurban Deep South. AIDS Care 2006;18(Suppl 1):S51-S58.

(19.) Berk ML, Schur CL, Dunbar JL, Bozzette S, Shapiro M. Short report: Migration among persons living with HIV. Soc Sci Med 2003;57(6):1091-97.

(20.) Harris NS, Dean HD, Fleming PL. Characteristics of adults and adolescents who have migrated from place of AIDS diagnosis to place of death, United States, 1993-2001. AIDS EducPrev 2005;17(6 Suppl B):39-48.

(21.) Rachlis B, Brouwer KC, Mills EJ, Hayes M, Kerr T, Hogg RS. Migration and transmission of blood-borne infections among injection drug users: Understanding the epidemiologic bridge. Drug Alcohol Depend 2007;90(2-3):107-19.

(22.) Delgado J, Heath KV, Yip B, Marion S, Alfonso V, Montaner JS, et al. Highly active antiretroviral therapy: Physician experience and enhanced adherence to prescription refill. Antivir Ther 2003;8(5):471-78.

Viviane D. Lima, PhD, [1,2] Eric Druyts, BA, [1] Julio S.G. Montaner, MD, FRCPC, FCCP, [1,2] Robert S. Hogg, PhD [1,3]

Author Affiliations

[1.] British Columbia Centre for Excellence in HIV/AIDS, Vancouver, BC

[2.] Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC

[3.] Faculty of Health Sciences, Simon Fraser University, Burnaby, BC

Correspondence: Viviane Dias Lima, HIV/AIDS Drug Treatment Program, BC Centre for Excellence in HIV/AIDS, 608-1081 Burrard Street, Vancouver, BC V6Z 1Y6, Tel: 604-806-8796, Fax: 604-806-9044, E-mail: [email protected]

Table 1. Mobility indicators, British Columbia, 1993-2005

(a) Inter-regional migration rates per 1000 population

                          First Residence Recorded

Last Residence Recorded   Interior        Fraser

Interior                  101             20
Fraser                    34              365
Vancouver Coastal         65              299
Vancouver Island          12              32
Northern                  5               10
Total                     217             726

                          Population      In
Region                    at Risk         Migrants

Interior                  175             74
Fraser                    732             367
Vancouver Coastal         2259            493
Vancouver Island          360             112
Northern                  62              31
Life-time migrants        3588            1077

(b) Concentration ratio, index of concentration and indice
of dissimilarity

                          Years

Indicators                1993 & 1996     1996 & 1999
                          %               %

Concentration ratio       39.5            45.9
Index of concentration    73.4            79.1
Index of dissimilarity    12.1            16.5

(a) Inter-regional migration rates per 1000 population

                          First Residence Recorded

Last Residence Recorded   Vancouver       Vancouver
                          Coastal         Island

Interior                  42              10
Fraser                    295             31
Vancouver Coastal         1766            117
Vancouver Island          56              248
Northern                  8               8
Total                     2167            414

                          Out             In-migration
Region                    Migrants        Rate

Interior                  116             422.9
Fraser                    361             501.4
Vancouver Coastal         401             218.2
Vancouver Island          166             311.1
Northern                  33              500.0
Life-time migrants        1077

(b) Concentration ratio, index of concentration and indice
of dissimilarity

                          Years

Indicators                1996 & 2001     1996 & 2003
                          %               %

Concentration ratio       49.8            54.1
Index of concentration    81.6            86.2
Index of dissimilarity    13.2            17.1

(a) Inter-regional migration rates per 1000 population

                          First Residence Recorded

Last Residence Recorded   Northern        Total

Interior                  2               175
Fraser                    7               732
Vancouver Coastal         12              2259
Vancouver Island          12              360
Northern                  31              62
Total                     64              3588

                          Out-migration   Net-migration
Region                    Rate            Rate

Interior                  662.9           -240.0
Fraser                    493.2           8.2
Vancouver Coastal         177.5           40.7
Vancouver Island          461.1           -150.0
Northern                  532.3           -32.3
Life-time migrants

(b) Concentration ratio, index of concentration and indice
of dissimilarity

                          Years

Indicators                1996 & 2005
                          %

Concentration ratio       57.4
Index of concentration    88.9
Index of dissimilarity    26