Mohammad Ehsanul KarimUniversity of British Columbia | UBC · School of Population and Public Health
Mohammad Ehsanul Karim
PhD
About
117
Publications
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Introduction
I am deeply interested in "causal inference" methodology.
Additional affiliations
Education
September 2009 - January 2015
September 2007 - August 2009
Publications
Publications (117)
Longitudinal observational data are required to assess the association between exposure to β-interferon medications and disease progression among relapsing-remitting multiple sclerosis (MS) patients in the "real-world" clinical practice setting. Marginal structural Cox models (MSCMs) can provide distinct advantages over traditional approaches by al...
http://www.bmj.com/content/347/bmj.f6651
Matched-cohort and nested case-control (NCC) analyses have been proposed as dynamic matching methods for exposure occurring over time. However, these methods might produce noisier estimates due to their matching mechanism. The literature suggests the consideration of multiple controls to reduce the variability in the effect estimates. In the presen...
Importance
Previous studies on the comparative effectiveness between buprenorphine and methadone provided limited evidence on differences in treatment effects across key subgroups and were drawn from populations who use primarily heroin or prescription opioids, although fentanyl use is increasing across North America.
Objective
To assess the risk...
Background
In many jurisdictions, policies restrict access to Opioid Agonist Treatment (OAT) in correctional facilities. Receipt of OAT during incarceration is associated with reduced risk of fatal overdose after release but little is known about the effect on nonfatal overdose. This study aimed to examine the association between OAT use during inc...
Introduction Comparative immunogenicity from different mRNA booster vaccines (directed at wild-type [WT], BA.1, or BA.4/5 antigens) remains unclear. Methods We included blood samples from adult paramedics who received three mRNA WT-directed vaccines plus a fourth dose of: (1) WT monovalent; (2) Moderna BA.1-WT bivalent; or (3) Pfizer BA.4/5-WT biva...
Recent research has highlighted the Omicron variant’s capacity to evade immune protection conferred by wild-type (WT) mRNA vaccines. Despite this observation, the potential involvement of antigenic sin phenomena remains unclear. Our hypothesis posited that a greater number of prior WT vaccine doses might lead to reduced anti-Omicron neutralization...
Background
HCV infection is associated with mortality due to extrahepatic manifestations (EHM). Sustained virologic response (SVR) following direct-acting antiviral (DAA) therapy has been linked to decreased all-cause and liver-related mortality. However, evidence regarding the impact of DAA on EHM-related deaths is lacking. This study aimed to ass...
Introduction : People with multiple sclerosis (MS) experience higher comorbidity burden than the non-MS population. Research has shown that having comorbidities alongside MS can lead to worse MS outcomes, including faster rates of disability progression, delays in initiating disease-modifying treatments, and earlier death. A comprehensive overview...
Background. We examined the 11 month longitudinal antibody decay among two-dose mRNA vaccinees, and identified factors associated with faster decay.
Methods. The study included samples from the COVID-19 Occupational Risk, Seroprevalence and Immunity among Paramedics (CORSIP) longitudinal observational study of paramedics in Canada. Participants wer...
This study investigated the association between previous SARS-CoV-2 infection and risk of symptoms associated with post COVID conditions among fully vaccinated paramedics in Canada. We included vaccinated paramedics who provided blood sample and questionnaire data on the same date during the study period. We examined the presence of symptoms associ...
Background
Recent data have demonstrated that healthcare use after treatment for respiratory tuberculosis (TB) remains elevated in the years following treatment completion. However, it remains unclear which TB survivors are high healthcare users and whether any variation exists within this population. Thus, the primary objective of this study was t...
Background
We examined the 11-month longitudinal antibody decay among 2-dose mRNA vaccinees, and identified factors associated with faster decay.Methods
The study included samples from the CORSIP longitudinal observational study of paramedics in Canada. Participants were included if they had received two mRNA vaccines without prior SARS-CoV-2 infec...
Background
We examined the 11-month longitudinal antibody decay among 2-dose mRNA vaccinees, and identified factors associated with faster decay.Methods
The study included samples from the CORSIP longitudinal observational study of paramedics in Canada. Participants were included if they had received two mRNA vaccines without prior SARS-CoV-2 infec...
Inverse Probability (of Adherence) Weighted per-protocol (IPW-PP) estimators are get- ting popular in addressing medication non-adherence while analyzing pragmatic trial data. However, their finite sample properties under different data generating mechanisms (DGMs) have not been investigated comprehensively. In the current work, we investigated the...
Background:
Despite data suggesting elevated morbidity and mortality among people who have survived tuberculosis disease, the impact of respiratory tuberculosis on healthcare utilization in the years following diagnosis and treatment remains unclear.
Methods:
Using linked health administrative data from British Columbia, Canada, we identified fo...
We investigated cardiovascular disease (CVD) risk associated with latent tuberculosis infection (LTBI) (Aim-1) and LTBI therapy (Aim-2) in British Columbia, a low-tuberculosis-incidence setting. 49,197 participants had valid LTBI test results. Cox proportional hazards model was fitted, adjusting for potential confounders. Compared with the particip...
Over 20 million adults in the United States live with High Impact Chronic Pain (HICP), or chronic pain that limits life or work activities for ≥3 months. It is critically important to differentiate people with HICP from those who sustain normal activities although experiencing chronic pain. Therefore, we aim to help clinicians and researchers ident...
Latent TB is associated with an increased CVD risk in a low-tuberculosis-incidence setting, with a higher risk associated with incomplete latent TB therapy and attenuated risk when therapy is completed.
Objectives:
Multimorbidity is the presence of two or more chronic health conditions. Tuberculosis (TB) survivors are known to have higher prevalence of multimorbidity, although prevalence estimates from high-income low-TB incidence jurisdictions are not available and potential differences in the patterns of chronic disease among TB survivors with...
Data on the contribution of hepatitis B virus (HBV) infection and related comorbidities to
liver-related mortality in Canada are limited. We assessed the concurrent impact of HBV infection, non-alcoholic fatty liver disease (NAFLD), and hepatitis C virus (HCV) coinfection on liver-related deaths in British Columbia (BC), Canada. We used data from t...
Background and objectives
Little is known of the potential sex and age differences in the MS prodrome. We investigated sex and age differences in healthcare utilization during the MS prodrome.
Methods
This was a population-based matched cohort study linking administrative and clinical data from British Columbia, Canada (population = 5 million). MS...
The relationship between antibodies to wild-type SARS-CoV-2 antigens and the risk of breakthrough infections is unclear, especially during time periods of Omicron. We investigated the association of anti-spike and anti-receptor binding domain antibody levels and the risk of subsequent breakthrough COVID-19. We included adult paramedics from an obse...
Live viral neutralizing antibody titers are an accepted measure of immunity; however, testing procedures are labor-intensive. COVID-19 antibody and angiotensin converting enzyme-2 (ACE-2) levels have been used as surrogates to live viral neutralizing antibody titers; however, validity among vaccinated individuals is unclear.
The SARS-CoV-2 belongs to the coronavirus family, which also includes common endemic coronaviruses (HCoVs). We hypothesized that immunity to HCoVs would be associated with stronger immunogenicity from SARS-CoV-2 vaccines. The study included samples from the COSRIP observational cohort study of adult paramedics in Canada. Participants provided blood...
Latent tuberculosis infection (LTBI) could increase the risk of cardiovascular disease (CVD), which is responsible for one-third of all global deaths. However, evidence is limited, with no evidence from low tuberculosis incidence settings like Canada, where tuberculosis is primarily concentrated among immigrants. In this study, we aimed to explore...
Pragmatic trials offer practical means of obtaining real‐world evidence to help improve decision‐making in comparative effectiveness settings. Unfortunately, incomplete adherence is a common problem in pragmatic trials. The commonly used methods in randomized control trials often cannot handle the added complexity imposed by incomplete adherence, r...
Last Observation Carried Forward (LOCF) is an ad-hoc method, with known limitations. In recent years, several methods publications have used LOCF in estimating the per-protocol effect via inverse probability of adherence weighted (IPAW) model, when a time-varying factor is partially measured by the study design. We compare the statistical performan...
Background
With many disease-modifying therapies currently approved for the management of multiple sclerosis, there is a growing need to evaluate the comparative effectiveness and safety of those therapies from real-world data sources. Propensity score methods have recently gained popularity in multiple sclerosis research to generate real-world evi...
Study objective
SARS-CoV-2 represents an occupational risk to paramedics, who work in uncontrolled environments. We sought to identify the occupation-specific risk to paramedics by comparing their seroprevalence of SARS-CoV-2 infection-specific antibodies to that of blood donors in Canada.
Methods
In this prospective cohort study, we performed ser...
Objective
Emerging evidence indicates that longer SARS-CoV-2 vaccine dosing intervals results in an enhanced immune response. However, the optimal vaccine dosing interval for achieving maximum immunogenicity is unclear.
Methods
This study included samples from adult paramedics in Canada who received two doses of either BNT162b2 or mRNA-1273 vaccin...
Purpose
: To explore the rheumatoid arthritis (RA)-cardiovascular diseases (CVD) association in relative and absolute risk scales among US adults aged ≥20 years over time and the effect modification of the association by age.
Methods
: We analyzed aggregated data from all ten continuous National Health and Nutrition Examination Survey cycles. A sa...
Among a cohort of adult paramedics in Canada, we investigated the performance of nucleocapsid (N) antibody detection (measured with a V-PLEX assay) to identify previous COVID-19 infections and compared differences among vaccinated and unvaccinated. Our data indicate that vaccinated and unvaccinated groups require different thresholds to achieve opt...
Background: Two-stage least square [2SLS] and two-stage residual inclusion [2SRI] are popularly used instrumental variable (IV) methods to address medication nonadherence in pragmatic trials with point treatment settings. These methods require assumptions, e.g., exclusion restriction, although they are known to handle unmeasured confounding. The ne...
Importance
Initiation of injection drug use may be more frequent among people dispensed prescription opioid therapy for noncancer pain, potentially increasing the risk of hepatitis C virus (HCV) acquisition.
Objective
To assess the association between medically dispensed long-term prescription opioid therapy for noncancer pain and HCV seroconversi...
Introduction
Unmeasured confounding poses a serious threat to observational studies of post-TB health outcomes. E-values have been recently proposed as a method to assess the magnitude of unmeasured confounding necessary to nullify, or to render non-significant, relative effect estimates from observational studies.
Methods
We calculated E-values f...
The optimal dosing interval for severe acute respiratory syndrome coronavirus 2 vaccines remains controversial. In this prospective study, we compared serology results of paramedics vaccinated with mRNA vaccines at the recommended short (17–28 days) vs long (42–49 days) interval. We found that a long dosing interval resulted in higher spike, recept...
Objective
To assess the association between long term prescription opioid treatment medically dispensed for non-cancer pain and the initiation of injection drug use (IDU) among individuals without a history of substance use.
Design
Retrospective cohort study.
Setting
Large administrative data source (containing information for about 1.7 million i...
Introduction: The instrumental variable (IV)-based methods (e.g., two-stage least square [2SLS], two-stage residual inclusion [2SRI], and nonparametric causal bound [NPCB]) can be used to address non-adherence in pragmatic trials. These methods require assumptions, e.g., exclusion restriction, although they are known to handle unmeasured confoundin...
Regular internet access is suggested to facilitate Comprehensive Correct HIV/AIDS Knowledge (CCAK). We assessed this association using the 2018 Nigeria Demographic Health Survey data, including 30,784 participants. CCAK was defined as knowing two primary HIV prevention methods, healthy-looking persons can have HIV, and rejecting two HIV misconcepti...
Purpose
Much of the extant research on quality-of-life (QoL) in homelessness has focused narrowly on health-related QoL. Far less is known about broader subjective quality-of-life (SQoL). The purpose of this study was to examine levels and predictors of SQoL among homeless and vulnerably housed individuals in a 4-year longitudinal study.
Methods
D...
Background
Interruptions in healthcare services contribute to an elevated risk of overdose in the weeks following release from incarceration. This study examined the association of use of community healthcare with nonfatal and fatal overdose in the 30 days following release.
Methods
We conducted a retrospective cohort study using linked administra...
Although the treatments are randomly assigned at baseline for pragmatic trials, subjects may deviate from the protocol because of switching to other treatments, loss to follow-up due to side-effects. An additional issue arises when there is an infrequent measurement frequency of post-randomization prognostic factors. Inability to adjust for non-adh...
Background
Hepatitis C virus (HCV) causes life-threatening chronic infections. Implementation of novel, economical or widely available screening tools can help detect unidentified cases and facilitate their linkage to care. We investigated the relationship between chronic HCV infection and a potential complete blood count biomarker (the monocyte-to...
Introduction
Increasing evidence indicates that chronic hepatitis C virus (HCV) infection is associated with higher risk of diabetes. Previous studies showed ethnic disparities in the disease burden of diabetes, with increased risk in Asian population. We described the incidence of type 2 diabetes related to HCV infection and assessed the concurren...
Purpose
: To estimate the risk of tuberculosis (TB)-associated depression. A second aim was to estimate the extent to which any increased risk of depression among TB patients may be mediated by the length of hospital length stay (LOS)
Methods
: Retrospective cohort study of linked healthcare claims and public health surveillance data. Our primary...
Background
The attained power, calculated conditional on the realized allocation, of a clinical trial may differ from the expected power, obtained pre-randomization through averaging over all potential allocations that could be generated by the randomization algorithm (RA). For example, a two-arm trial using a RA that is expected to allocate 20 par...
The measurement frequency of post-randomization prognostic factors in pragmatic clinical trials is typically infrequent. The inverse probability of adherence weighting (IPAW) method has been shown to substantially reduce the per-protocol effect estimate’s bias if those unmeasured longitudinal values are imputed more frequently. Previous application...
Introduction: Instrumental variable (IV)-based methods (e.g., two-stage least square [2SLS], two-stage residual inclusion [2SRI], and nonparametric causal bound [NPCB]) can be used to address non-adherence in pragmatic trials. These methods require assumptions, e.g., exclusion restriction, although they are known to handle unmeasured confounding. I...
Objective
Depression is a highly-prevalent disorder among US adults and despite advancements in treatment options, prevalence rates are increasing. With the emerging recommendations of dietary interventions such as high fish intake come potential risks, for example, exposure to methylmercury (MeHg). Case reports and animal models have suggested a p...
Participants in pragmatic clinical trials often partially adhere to treatment. However, to simplify the analysis, most studies dichotomize adherence (supposing that subjects received either full or no treatment), which can introduce biases in the results. For example, the popular approach of principal stratification is based on the concept that the...
Background
The 2018 World Health Organization HIV guidelines were based on the results of a network meta-analysis (NMA) of published trials. This study employed individual patient-level data (IPD) and aggregate data (AgD) and meta-regression methods to assess the evidence supporting the WHO recommendations and whether they needed any refinements....
Background: Administrative databases do not contain Body Mass Index (BMI) informa- tion. In proportion-based imputation (PBI) technique, a BMI category is assigned to an individual according to the proportions observed in external survey data. Alternatively, BMI can be imputed using Multiple Imputation (MI). Objectives: To compare MI with PBI to im...
Background
Current epidemiological evidence of post-TB airway disease is largely cross-sectional and derived from high-TB-incidence settings. We present the first cohort study of post-TB airway disease in a low-TB-incidence setting.
Aims
(1) analyze the risk of airway disease by respiratory TB, (2) assess potential unmeasured confounding between T...
Background
The use of individual patient data (IPD) in network meta-analyses (NMA) is rapidly growing. This study aimed to determine, through simulations, the impact of select factors on the validity and precision of NMA estimates when combining IPD and aggregate data (AgD) relative to using AgD only.
Methods
Three analysis strategies were compare...
Vitamin A deficiency (VAD) may cause anemia. The research aimed at evaluating the effect of Vitamin A supplementation (VAS) on hemoglobin (Hb) is, however, limited and, conclusions drawn from a few studies have been concluded inconsistently. In Bangladesh, the prevalence of childhood anemia is high, as well as the prevalence of VAD. Therefore, the...
Background
Current human papillomavirus (HPV) vaccine coverage in the United States (in 2019, 66–70%), remains below the Healthy People 2020 coverage goal of 80%. HPV vaccine misinformation, including parental concerns of sexual risk-compensation influence vaccine uptake. We examined the association between HPV vaccination and sexually transmitted...
Background
Propensity score (PS) analyses are increasingly used in multiple sclerosis (MS) research, largely owing to the greater availability of large observational cohorts and registry databases.
Objective
To evaluate the use and quality of reporting of PS methods in the recent MS literature.
Methods
We searched the PubMed database for articles...
Background: To address treatment nonadherence, many statistical methods are proposed: the naïve methods (e.g., intention-to-treat, naïve per-protocol, and as-treated), inverse probability-weighted per-protocol (IP-weighted PP), and instrumental variable (IV)-based methods (e.g., two-stage least square (2SLS), two-stage residual inclusion (2SRI), an...
The beta-interferons are widely prescribed platform therapies for patients with multiple sclerosis (MS). We accessed a cohort of patients with relapsing onset MS from British Columbia, Canada (1995-2013) to examine the potential survival advantage associated with beta-interferon exposure using a marginal structural model. Accounting for potential t...
Background
To inform World Health Organization (WHO) global guidelines, we updated and expanded the evidence base to assess the comparative efficacy, tolerability, and safety of first-line antiretroviral therapy (ART) regimens.
Methods
We searched Embase, Medline and CENTRAL on 28 February 2020 to update the systematic literature review of clinica...
Background:
Despite Canada's universal health-care system, millions of Canadians experience unmet health-care needs (UHCN). People with mood disorders may be at higher risk of UHCN due to barriers such as stigma and gaps in health-care services.
Aim:
We aimed to examine the relationship between having a diagnosed mood disorder and experiencing U...
Introduction:
Despite a recent meta-analysis including 31 randomised controlled trials comparing methadone and buprenorphine for the treatment of opioid use disorder, important knowledge gaps remain regarding the long-term effectiveness of different treatment modalities across individuals, including rigorously collected data on retention rates and...
- From the simulation, we found that the naïve PP, naïve AT, and IPCW methods prone to give biased estimates in the pragmatic trials. The naïve PP and AT estimates are biased due to non-random adherence, and the IPCW estimates can be biased due to the artificial censoring mechanism.
- To address nonadherence in the pragmatic trials, we can use the...
In veneer-drying facilities, controllers face many challenges to maintain desired parameters in the final product based on customer’s needs. The major challenge is setting process parameters to control the temperature and humidity within the various sections in the drying machine to obtain the desired properties of the final product. The regression...
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Objective
To compare non-tuberculosis (non-TB)-cause mortality risk overall and cause-specific mortality risks within the immigrant population of British Columbia (BC) with and without TB diagnosis through time-dependent Cox regressions.Methods
All people immigrating to BC during 1985–2015 (N = 1,030,873) were included with n = 2435 TB patients, an...
Background:
In a cross-sectional stepped-wedge trial with unequal cluster sizes, attained power in the trial depends on the realized allocation of the clusters. This attained power may differ from the expected power calculated using standard formulae by averaging the attained powers over all allocations the randomization algorithm can generate. We...
Pragmatic trials offer practical means of obtaining real-world evidence (RWE) to help improve decision-making in comparative effectiveness settings. Analyzing these trial data are, however, particularly challenging in the presence of incomplete adherence (e.g., due to treatment discontinuation/switching). A wide variety of statistical methods are p...
Study design:
Protocol for a pragmatic randomized controlled trial (the Exercise guideline Promotion and Implementation in Chronic SCI [EPIC-SCI] Trial).
Primary objectives:
To test if home-/community-based exercise, prescribed according to the international SCI exercise guidelines, significantly reduces chronic bodily pain in adults with SCI....
Background In a cross-sectional stepped-wedge trial with unequal cluster sizes, attained power in the trial depends on the realized allocation of the clusters. This attained power may differ from the expected power calculated using standard formulae by averaging the attained power over all allocations the randomization algorithm can generate. We in...
Background In a cross-sectional stepped-wedge trial with unequal cluster sizes, attained power in the trial depends on the realized allocation of the clusters. This attained power may differ from the expected power calculated using standard formulae by averaging the attained powers over all allocations the randomization algorithm can generate. We i...
The present study examined the association of residential instability with hospitalizations among homeless and vulnerably housed individuals over a 4-year time period. Survey data were linked to administrative records on hospitalizations. Specifically, we used data from the Health and Housing in Transition study, a prospective cohort study that tra...
Background:
Maternal and child mortality remain a global health concern despite different interventions that have been implemented to address this issue. Adequate antenatal care (ANC) is crucial in reducing maternal and neonatal morbidity and mortality. However, in Rwanda, there is still suboptimal utilization of ANC services. This study aims to a...
Abstract Health researchers are familiar with the concept of