PubMed Health⌕ Search

Biomedical subjects

Mark Tyndall

Publications and source records attributed to Mark Tyndall.

At least 19 recordsLinked to original sources
PubMed2007

Changes in injecting practices associated with the use of a medically supervised safer injection facility.

Injection drug users (IDUs) are vulnerable to serious health complications resulting from unsafe injection practices. We examined whether the use of a supervised safer injection facility (SIF) promoted change in injecting practices among a representative sample of 760 IDUs who use a SIF in Vancouver, Canada. Consistent SIF use was compared with inconsistent use on a number of self-reported changes in injecting practice variables. More consistent SIF use is associated with positive changes in injecting practices, including less reuse of syringes, use of sterile water, swabbing injection sites, cooking/filtering drugs, less rushed injections, safe syringe disposal and less public injecting.

Adult↗
PubMed2006

Using latent class analysis (LCA) to analyze patterns of drug use in a population of illegal opioid users.

BACKGROUND: The objective of this paper is to empirically determine a categorization of illegal opioid users in Canada in order to describe and analyze drug use patterns within this population. METHODS: Drug use patterns of 679 eligible illegal opioid users outside treatment from the OPICAN study, a pan-Canadian cohort (recruited March to December, 2002) involving the cities of Toronto, Montreal, Vancouver, Edmonton and Quebec City, were empirically examined using latent class analysis. These latent classes were then further analyzed for associations using chi-square and t-test statistics. FINDINGS: The opioid and other drug user sample surveyed were categorized into three latent classes. Class 1 (N=256) was characterized by the use of Tylenol 3 and benzodiazepines along with high levels of depression and self-reported pain. Class 2 (N=68) was described by the non-injection use of both heroin and crack while having a high level of homelessness. Class 3 (N=344) was shown to consist of injection drug users of heroin and cocaine exhibiting the highest levels of HIV and Hepatitis C infections amongst the classes. CONCLUSIONS: Using latent class analysis we found distinct patterns of drug use amongst illegal opioid users differing in terms of type of drugs co-used, social context, and co-morbid pathologies. These data may be useful as the empirical basis for the planning of specific prevention and treatment interventions.

Acetaminophen↗
PubMed2006

Predictors of non-fatal overdose among a cohort of polysubstance-using injection drug users.

BACKGROUND: Non-fatal overdose is a major determinant of morbidity among injection drug users (IDU). We sought to evaluate factors associated with non-fatal overdose among IDU in Vancouver. METHODS: We examined non-fatal overdose among participants in the Vancouver Injection Drug Users Study. Correlates of non-fatal overdose occurring between 1996 and 2004 were identified using generalized estimating equations (GEE). RESULTS: There were 1587 participants included in this analysis, including 576 (36%) women. At baseline, 750 (47%) reported a history of non-fatal overdose. In total, 985 reports of non-fatal overdose were made during follow-up by 519 (32.7%) participants. In multivariate GEE analyses, factors independently associated with non-fatal overdose included: heroin injection (AOR=2.67), cocaine injection (AOR=2.01), benzodiazepine use (AOR=2.00), requiring help injecting (AOR=1.58), binge drug use (AOR=1.52), homelessness (AOR=1.38), alcohol use (AOR=1.32), street injecting (AOR=1.22), non-injectable opiate use (AOR=1.16), speedball use (AOR=1.15), and recent incarceration (AOR=1.14). Younger age (AOR=0.99) and methadone use (AOR=0.51) were protective. CONCLUSIONS: We found that non-fatal overdose was common among local IDU. Non-fatal overdose was associated with several factors that may be amenable to intervention, including opiate and stimulant use, and the characteristic of requiring help with injecting. These findings indicate the need for the ongoing development of structural interventions to address this common cause of morbidity among IDU.

Adolescent↗
PubMed2006

Disease progression in patients with virological suppression in response to HAART is associated with the degree of immunological response.

OBJECTIVE: To determine if immunological response is associated with disease progression in patients with virological suppression after initiating HAART. DESIGN: A cohort study of 1084 treatment-naive participants in the British Columbia HIV/AIDS Drug Treatment Program who had achieved viral loads < 500 copies/ml at 3-9 months after initiating triple-drug therapy. METHODS: Cox proportional hazards was used to model the association with disease progression of baseline variables, change in CD4 cell counts and CD4 cell count strata at 6 months. Logistic regression analysis was used to examine associations with two definitions of poor immunological response. RESULTS: Patients were followed for a median of 51.4 months. In univariate analyses, increases in CD4 cell counts of < 25 cells/microl and absolute CD4 cell counts of < 200 cells/microl were associated with an increased risk of death or new AIDS events. Two mulitivariate models, one including baseline CD4 cell count and change in CD4 cell count from baseline and the other including only absolute CD4 cell counts at 6 months, were found to predict disease progression in this setting. Increases in CD4 cell count of < 25 cells/microl were associated with increasing age and inversely associated with low baseline CD4 cell counts, high baseline viral loads and good adherence to therapy. CD4 cell counts of < 200 cells/microl at 6 months were associated with low baseline CD4 cell counts and having AIDS at baseline. CONCLUSION: Patients with virological suppression are still at risk for HIV disease progression if adequate immunological responses are not achieved.

Adult↗
PubMed2006

Impact of a medically supervised safer injection facility on community drug use patterns: a before and after study.

PROBLEM: Illicit use of injected drugs is linked with high rates of HIV infection and fatal overdose, as well as community concerns about public drug use. Supervised injecting facilities have been proposed as a potential solution, but fears have been raised that they might encourage drug use. DESIGN: A before and after study. Participants and setting 871 injecting drug users recruited from the community in Vancouver, Canada. KEY MEASURES FOR IMPROVEMENT: Rates of relapse into injected drug use among former users and of stopping drug use among current users. STRATEGIES FOR CHANGE: Local health authorities established the Vancouver supervised injecting facility to provide injecting drug users with sterile injecting equipment, intervention in the event of overdose, primary health care, and referral to external health and social services. EFFECTS OF CHANGE: Analysis of periods before and after the facility's opening showed no substantial increase in the rate of relapse into injected drug use (17% v 20%) and no substantial decrease in the rate of stopping injected drug use (17% v 15%). LESSONS LEARNT: Recently reported benefits of supervised injecting facilities on drug users' high risk behaviours and on public order do not seem to have been offset by negative community impacts.

Adult↗
PubMed2006

Crack across Canada: Comparing crack users and crack non-users in a Canadian multi-city cohort of illicit opioid users.

AIMS: To examine possible differences between crack users and crack non-users across Canada. DESIGN: Cohort study of illicit opioid and other drug users in five cities across Canada. SETTING: Vancouver, Edmonton, Toronto, Montreal and Quebec City, Canada. PARTICIPANTS: Regular illicit opioid and other street drug users not in treatment at time of assessment. MEASUREMENTS: Participants (n = 677) were assessed at baseline (2002) by way of an interviewer-administered questionnaire, a psychiatric diagnostic instrument (Composite International Diagnostic Interview), and salivary antibody tests for infectious disease. FINDINGS: Approximately half the sample had used crack in the past 30 days, although prevalence rates differed strongly between study sites. When examined by discriminant analysis, crack users in the study population were more likely to have: no permanent housing, have illegal and sex work income, indicate physical health problems and hepatitis C virus (HCV) antibodies, use walk-in clinics, use heroin and to have been arrested and in detention (in past year). They were less likely to report depressive symptoms, and use Dilaudid (hydromorphone) and alcohol. CONCLUSION: These results illustrate crack users' pronounced social marginalization (as expressed by homelessness and high involvement in illegal activities) as well as extensive health problems compared to non-crack users in the Canadian context. The development of targeted interventions-addressing the dynamics of social marginalization-of this population is urgently needed.

Adult↗
PubMed2006

EMF issues must be fully managed.

Commanding increased attention are issues relating to electromagnetic fields (EMFs) in the workplace and a new EC Directive. Technical report by Dr Didier Bozec DUT (France) BSc (Hons) PhD MIEE MIEEE MIHEEM, laboratory manager, York EMC Services; and Dr Mark Tyndall MPhys (Hons) PhD, engineer, York EMC Services.

Electromagnetic Fields↗
PubMed2005

Discordant immunologic and virologic responses to highly active antiretroviral therapy are associated with increased mortality and poor adherence to therapy.

OBJECTIVE: To examine the independent association of discordant virologic and immunologic responses to highly active antiretroviral therapy (HAART) with mortality. METHODS: A population-based study of 1527 treatment-naive individuals initiating HAART used Cox proportional hazards modeling to determine the independent association of treatment response at 3 to 9 months with nonaccidental mortality. Logistic regression was used to examine associations with discordant responses. RESULTS: Viral load (VL)/CD4 discordant responses were seen in 235 (15.4%) of subjects, and VL/CD4 responses were seen in 179 (11.7%) of subjects. In adjusted Cox regression models, discordant responses were found to be independently associated with an increased risk of mortality (VL/CD4: relative hazard [RH] = 1.87, 95% confidence interval [CI]: 1.15 to 3.04; VL/CD4: RH = 2.47, 95% CI: 1.54 to 3.95). VL/CD4 discordance was found to be associated with increasing age, baseline HIV RNA load <100,000 copies/mL, baseline CD4 counts <50 cells/muL, the use of lamivudine (3TC)/zidovudine (ZDV), and poor adherence to therapy. VL/CD4 discordance was associated with younger age; injection drug use; baseline HIV RNA load >100,000 copies/mL; the use of 3TC/ZDV, didanosine (ddI)/3TC, or ddI/stavudine; and poor adherence to therapy. CONCLUSION: Discordant responses are independently associated with an increased risk of mortality and are, in turn, associated with poor adherence to therapy.

Adult↗
PubMed2005

Illicit opioid use in Canada: comparing social, health, and drug use characteristics of untreated users in five cities (OPICAN study).

Most of the estimated 125,000 injection drug users (IDUs) in Canada use illicit opioids and are outside treatment (i.e., methadone maintenance treatment). Empirical data suggest that illicit opioid users outside treatment are characterized by various health and social problem characteristics, including polydrug use, physical and mental morbidity, social marginalization, and crime. Although required for evidence-based programming, systematic information on this specific substance-user population is sparse in Canada to date. This article presents and compares key characteristics of population of illicit opioid users outside treatment in five cities across Canada (OPICAN cohort). Overall, the majority of OPICAN participants regularly used both a variety of illicit opioids and cocaine or crack, reported physical and mental health (e.g., mood disorder) problems, lacked permanent housing, were involved in crime, and had their "ideal" treatment not available to them. However, key local sample differences were shown, including patterns of heroin versus prescription opioid use and levels of additional cocaine versus crack use as well as indicators of social marginalization. Illicit opioid user population across Canada differ on key social, health, and drug use indicators that are crucial for interventions and are often demonstrated between larger and smaller city sites. Differentiated interventions are required.

Adult↗
PubMed2005

Comorbid depression among untreated illicit opiate users: results from a multisite Canadian study.

OBJECTIVES: This study aimed to describe patterns of major depression (MDD) in a cohort of untreated illicit opiate users recruited from 5 Canadian urban centres, identify sociodemographic characteristics of opiate users that predict MDD, and determine whether opiate users suffering from depression exhibit different drug use patterns than do participants without depression. METHOD: Baseline data were collected from 679 untreated opiate users in Vancouver, Edmonton, Toronto, Montreal, and Quebec City. Using the Composite International Diagnostic Interview Short Form for Major Depression, we assessed sociodemographics, drug use, health status, health service use, and depression. We examined depression rates across study sites; logistic regression analyses predicted MDD from demographic information and city. Chi-square analyses were used to compare injection drug use and cocaine or crack use among participants with and without depression. RESULTS: Almost one-half (49.3%) of the sample met the cut-off score for MDD. Being female, white, and living outside Vancouver independently predicted MDD. Opiate users suffering from depression were more likely than users without depression to share injection equipment and paraphernalia and were also more likely to use cocaine (Ps < 0.05). CONCLUSIONS: Comorbid depression is common among untreated opiate users across Canada; targeted interventions are needed for this population.

Adult↗
PubMed2004

Determinants of overdose incidents among illicit opioid users in 5 Canadian cities.

BACKGROUND: Drug overdose is a major cause of death and illness among illicit drug users. Previous research has indicated that most illicit drug users experience nonfatal overdoses and has suggested a variety of factors that are associated with risk of overdose. In this study, we examined the occurrence of and the factors associated with nonfatal overdoses within a Canadian sample of illicit opioid users not enrolled in treatment at the time of study recruitment. METHODS: Interviewers used a standard questionnaire to collect data on sociodemographic characteristics, drug use, health and health care, experience in the criminal justice system and treatment for drug problems; they also performed standard assessments for mental health and infectious disease. The association between overdose and sociodemographic and drug-use factors was examined with chi(2) and t test analyses; marginally significant variables were examined with logistic regression to determine independent effects. RESULTS: A total of 679 subjects were interviewed; 651 provided answers sufficient for this analysis. One hundred and twelve (17.2%) of the 651 respondents reported an overdose episode in the previous 6 months. In the logistic regression analysis (after adjustment for sociodemographic factors), homelessness, noninjection use of hydromorphone in the past 30 days and involvement in drug treatment in the past 12 months were predictors of overdose (p < 0.05). INTERPRETATION: Overdose poses a considerable health risk for illicit opioid users. We found that a diverse set of factors was associated with overdose episodes. Prevention efforts will likely be more effective if they can be directed to specific causal factors.

Adult↗
PubMed2004

Psychosocial determinants of adherence to highly active antiretroviral therapy among injection drug users in Vancouver.

BACKGROUND: Sub-optimal adherence to highly active antiretroviral therapy (HAART) among injection drug users (IDUs) is a significant concern. As such, there is an urgent need to identify psychosocial determinants of adherence that can be incorporated into interventions designed to promote optimal adherence. OBJECTIVE: To identify psychosocial determinants of adherence to HAART, as well as self-reported reasons for missing doses of HAART among HIV-infected IDUs. METHODS: We developed an eight-item adherence self-efficacy scale comprised of two sub-scales: adherence efficacy and self-regulatory efficacy. We examined correlates between adherence self-efficacy, outcome expectations, socio-demographic characteristics, drug use and risk behaviours, social support and HAART adherence among 108 HIV-infected participants in the Vancouver Injection Drug Users Study (VIDUS). Pharmacy-based adherence to HAART was obtained through a confidential record linkage to the province of British Columbia's HIV/AIDS Drug Treatment Program. Participants were defined as adherent if they picked-up 95% of their HAART prescriptions. Participants were also asked to indicate reasons for missing doses of HAART. Logistic regression was used to identify the factors independently associated with adherence to HAART. RESULTS: Seventy-one (66%) HIV-infected IDUs were less than 95% adherent. Forgetting was the most frequently cited reason (27%) for missing doses of HAART. Factors independently associated with adherence to HAART included adherence efficacy expectations [OR=1.8 (95% CI: 1.0-3.1); P=0.039] and negative outcome expectations [OR=0.8 (95% CI: 0.7-0.9); P=0.027]. CONCLUSIONS: We found low rates of adherence to HAART among IDUs. Psychological constructs derived from self-efficacy theory are highly germane to the understanding of adherence behaviour, and interventions that address these constructs should be developed and tested among HIV-infected drug users.

Adult↗
PubMed2003

Impaired virologic response to highly active antiretroviral therapy associated with ongoing injection drug use.

Injection drug users who continue to use drugs may not respond to highly active antiretroviral therapy (HAART) as well as other HIV-infected individuals, even after adjusting for a reliable measure of adherence. We therefore compared the virologic response among participants in a population-based HIV/AIDS Drug Treatment Program in British Columbia, Canada, by injection drug use activity. Participants who were HIV infected and naive to antiretroviral therapy and who were prescribed antiretroviral treatment between August 1996 and December 2000 were eligible for this study. They were classified as current, former, or non-injection drug users. The main outcome was having two consecutive HIV-1 RNA levels less than 500 copies/mL. We used logistic regression to adjust for baseline HIV-1 RNA, type of antiretroviral regimen (2 nucleosides + nonnucleoside reverse transcriptase inhibitor versus 2 nucleosides + protease inhibitor), duration of therapy (months), adherence (derived from refill compliance data), and age. A total of 578 participants were first prescribed HAART during the study period. Among them, 78 (13%) were current injection drug users, 96 (17%) were former injection drug users, and 404 (70%) never injected drugs. In the multivariable logistic regression, relative to non-drug users, current injection drug users were significantly less likely to suppress their HIV-1 RNA (adjusted OR [AOR] = 0.30, 95% CI: 0.13-0.67), and former injection drug users were not significantly different from non-drug users (AOR = 0.56, 95% CI: 0.24-1.34). There was a significant interaction between drug use and adherence. In the analyses stratified by drug use, the adherence of former and non-drug users was positively associated with HIV-1 RNA suppression (AOR = 1.33, 95% CI: 1.14-1.55), whereas for current drug users, it was not (AOR = 1.07, 95% CI: 0.87-1.33). Current injection drug users were less likely to achieve HIV-1 RNA suppression compared with non-drug users. Adherence as measured by pharmacy refill compliance was not a reliable measure in this subpopulation.

Adult↗
PubMed2003

Sexual violence among a cohort of injection drug users.

The objective of this study was to determine the prevalence of, and factors associated with, sexual violence in childhood, adolescence and adulthood, among injection drug using men and women. The Vancouver Injection Drug User Study is a prospective cohort of injection drug users (IDU) begun in 1996. The analysis included all individuals who completed the baseline questionnaire who responded to a question about sexual assault. Multivariate modeling was used to determine and to what extent a history of sexual violence at different ages is predictive of HIV risk and other health risk behaviors. HIV prevalence was calculated as the total current number of HIV-positive individuals in the cohort. Of the 1437 eligible individuals, 36% reported a lifetime history of sexual violence; 68% of women, and 19% of men (p<0.001). After adjusting for fixed sociodemographics, these individuals were more likely to have ever been in the sex trade, to knowingly share needles/rigs with HIV-positive people, to have attempted suicide, to have ever accidentally overdosed, to binge on alcohol, and to have been diagnosed with a mental disorder/disability. The prevalence of child sexual abuse in this cohort is 21%; 33% for women, and 13% for men. The data show a dose-response relationship between age at first sexual violence and most risk behaviors examined. These relationships are further mediated by gender. The prevalence of HIV among individuals who ever experienced sexual violence was 25%, compared to 19% among those who never experienced sexual violence (p=0.006). Sexual violence, and especially child sexual abuse, is highly prevalent among this cohort, particularly among women. Child sexual abuse has worse consequences for both genders than sexual violence later in life. Nevertheless, women and men are affected differently by sexual violence at different ages, and this has significant implications for health promotion programs, and specifically HIV prevention.

Adolescent↗
PubMed2002

Risk-taking behaviors among injecting drug users who obtain syringes from pharmacies, fixed sites, and mobile van needle exchanges.

Needle-exchange programs (NEPs) have been shown to be effective in reducing harm related to injection drug use and to act as an important link between the injection drug using community and preventive/treatment services. Different needle-exchange distribution methods may reach different subpopulations of injecting drug users (IDUs). We undertook this study to characterize risk behaviors by primary source of clean needles accessed by IDUs in a city with pharmacy access and fixed and mobile exchange programs. We hypothesized there would be a gradient of risk across the three types of distribution. Data were collected from within the Vancouver Injection Drug Users Study (VIDUS), a prospective cohort study. Participants who primarily obtained clean needles from pharmacies, fixed sites, or mobile exchange vans were compared using the Cochran-Armitage trend test to test for trends in increasing risk behaviors across the three types of distribution. Ordinal multivariate regression was used to adjust the associations for potential confounders. Results illustrate clear trends for increasing risk profiles from pharmacy to fixed site to mobile exchange vans. Van users were generally at higher risk than fixed-site and pharmacy users. Independent predictors of van use were fewer years injecting, difficulty finding needles, Aboriginal ethnicity, incarceration in the previous 6 months, and injecting cocaine daily. An important component of needle-exchange programs is outreach to access those who are at highest risk. Use of distribution beyond fixed sites will improve such outreach, thereby increasing program effectiveness and further preventing the transmission of blood-borne infections.

Adult↗