The Economic Burden of Asthma in Canada
Condition: Asthma
MeSH terms: Asthma; Financial Stress
Study type: Observational

Summary: 
      The study will consist of three phases: Phase A: General population survey for estimation of
      the prevalence of asthma, and prospective collection of resource utilization and
      quality-of-life data for 12 months, Phase B: comparison of healthcare resource usage
      collected prospectively to the data collected using administrative data in the population
      recruited in Phase A, and Phase C: Economic modeling of asthma to extrapolate the findings
      across Canada and into the future years.
    

Detailed description: 
      Phase A: This phase will be a prospective cohort study of randomly chosen residents of two
      census subdivisions of BC with a self-reported physician diagnosis of asthma. The study
      participants will be recruited via landline and cell phone-based random digit dialing across
      two regions in British Columbia: the Census Sub-Division of the city of Vancouver and the
      Census Division of Central Okanagan. The target area was chosen based on Census Sub-Division
      as it provides a clear definition of the target population for whom demographic and
      socioeconomic data is available through national and provincial census and surveys. The
      Okanagan Census Sub-Division was particularly chosen as it provides data on both urban and
      rural populations (18.6% rural population in 2006). According to 2006 census profile, the
      population of these two Census Sub-Divisions is, respectively, 578,041 and 162,276.
      Accordingly, about 78% of participants would be recruited from Vancouver, and 22% from
      Okanagan. The study will randomly sample participants from all the area codes in these
      regions. The target population will include household residents residing in telephone
      exchanges within the target Census Sub-Divisions. Random digit dialing will be geographically
      stratified with an associated sample weight that will approximate a probability sample of the
      individuals in the population. Previous studies have shown that acceptably high response
      rates can be achieved among Canadian participants with asthma.

      Random digit dialing samples have been shown to be more representative than population
      samples drawn using alternative methods such as telephone directories or electronic white
      pages. However, random digit dialing is not free of bias. Non-random non-response is an
      issue, and it has been shown that reducing the non-response rate may directly reduce
      non-response bias. Non-responders in random digit dialing may not have been contacted because
      the non-responders work multiple minimum-wage jobs. The investigators will place multiple
      calls and leave messages on answering machines. Random digit dialing is also subject to
      no-telephone bias - households without telephones are out of reach by random digit dialing,
      and the households without telephones probably differ in socioeconomic status than the
      overall population. However, for the urban, suburban, and semi-rural sub-populations within
      British Columbia, telephone coverage is almost universal.

      Inclusion of cell phones in random digit dialing is an attempt to mitigate such biases and
      increase the fraction of population covered by sampling. More importantly, the inclusion of
      cell phones is likely to result in inclusion of participants that might be absent from
      landline random digit dialing (younger and more educated groups) thus mitigating the sampling
      bias of random digit dialing. Cell phone random digit dialing is an active area of research
      and it is too soon to know with confidence what should and should not be regarded as a "Best
      Practice". For inclusion of cell phones in random digit dialing, the investigators will use
      the "Screening Approach". In this approach the interview is only conducted with participants
      sampled via the cell phone frame who do not have a landline, thus excluding numbers from the
      cell phone sample in the overlap (i.e., screening out the participants with both a cell phone
      and a landline). In this alternative sampling design, participants who have at least one
      household landline telephone and use at least one cell phone would be eligible for inclusion
      only from the landline frame. This decreases the bias due to higher probability of sampling
      from households who have both a landline and cell phone.

      The study will employ the Waksberg method of random digit sampling. In this method, all
      telephone numbers are initially split into blocks of equal size, called "primary sampling
      units". The primary sampling unit will be a mixture of landlines and cell phones. One
      randomly selected telephone number is called from each selected primary sampling unit. When a
      residential connection is reached in the first stage, the primary sampling unit qualifies for
      inclusion in the second stage.

      Respondents will be asked the following question: "Is there a member of the household between
      ages of 1 to 85 who has had asthma ever diagnosed by a physician". If the response is
      affirmative the study assistant will ask if the participant in question can continue the
      conversation directly (parents in case of children). Eligible participants (or in the case of
      children their parents or guardians) will be informed of the objectives of the study,
      verbally consented, and then screened for eligibility based on age and history of asthma.
      Participants who meet eligibility criteria and verbally consent over the phone will be asked
      to come to the study laboratory (one at Vancouver and one at Kelowna, corresponding to the
      two Census Sub-Divisions) and the participant will receive a detailed explanation of the
      study and the study consent form at that time.

      All participants who provide signed consent will then proceed to spirometry (simple
      spirometry without bronchodilator response) and study data collection. After the baseline
      visit, participants enter a 12-months period of follow-up with visits at months 3, 6, 9, and
      12. Participants will be asked to attend one of the study centres and data on the quality of
      life and asthma-related resource utilization will be gathered. On the final visit,
      participants will undergo spirometry for objective diagnosis of asthma with possible
      methacholine challenge test for the participants whose asthma cannot reliability be included
      or excluded.

      Phase B: In this phase of the study, health records of participants who have participated in
      the phase A of the study for the entire follow-up period and the 12 months period prior to
      the participants' enrolment will be retrieved from the BC Linked Health Database. In
      addition, the investigators will identify cases of asthma in the entire British Columbia
      population based on the administrative data for the same period of time. The BC Linked Health
      Database is a longitudinal administrative health care database containing
      participant-specific, anonymized health data from 1985 onwards on British Columbia's 4
      million residents with health insurance. Records will be matched based on participants'
      unique Personal Health number and hence the matching will be almost completely accurate. Data
      extracted from the BC Linked Health Database will include Medical Services Plan data, which
      encompass fee-for-service physicians, the Discharge Abstracts Database of hospital inpatient
      separation records, as well as records of death certificates. Prescription drug use will be
      determined from the BC Pharmanet database. This is a population-based prescription drug
      database that captures essentially all dispensing episodes by outpatients residing in the
      province on a prescription-by-prescription basis (regardless of funding source)..

      One request thought the British Columbia ministry of health (personal communication with Data
      Stewardship Secretariat) is required to retrieve data on the study participants as well as
      cases of asthma across the entire province, without additional cost for the latter group. The
      investigators will use this opportunity to retrieve data on cases of asthma in the entire
      province and compare different aspects of resource utilization between objectively verified
      cases of asthma and the data retrieved using a case definition algorithm on an administrative
      database. Such data will be used to retrospectively estimate the direct costs of asthma
      during the follow-up and in the 12 months prior to the enrolment in the study. The direct
      medical costs calculated in this way will be compared with the direct costs calculated in the
      prospective phase of the study. In addition, the investigators will examine the
      representativeness of the sample population by comparing the participant's health records
      with case of asthma in British Columbia identified through the BC Linked Health Database.
      Given the objective validation of the diagnosis of asthma at the end of the follow-up period
      in Phase A, the investigators will also be able to explore the sensitivity of existing case
      ascertainment algorithms based on administrative data at levels of severity and control.

      Phase C: Economic model of asthma: The data collected from participants during this study
      will be extrapolated to the population of British Columbia and Canada by appropriate
      adjustment for demographic and socioeconomic differences and reported prevalence of asthma in
      the country. The data will also be used to populate a Markov model of asthma to project the
      burden of asthma for the next 10 years. The Markov model of asthma will extend the model
      previously developed by Price et al. However, the investigators will model all 4 states of
      severity as defined by the Global Initiative in Asthma and whether at each year the
      participant's symptoms are controlled or uncontrolled. The Markov model will hence consist of
      8 states (plus state of death) for all permutations of levels of severity and control. The
      model will also incorporate both the steady-state of chronic asthma and the acute state
      associated with an asthma exacerbation. Whenever possible, the investigators will estimate
      the parameters of the model from the cohort of participants in the Phase A and B of the
      study. This will include the initial distribution of individuals according to levels of
      severity and control, and the quality of life weights and annual direct and indirect costs
      estimated from the statistical analysis of the cohort data. The long term transition
      probabilities among levels of severity and control cannot reliably be estimated given the
      short follow-up of the participants in this study. The investigators will use values
      estimated from the literature for these and other components of the model.
    

Intervention name(s): breathing test
Intervention type(s): Diagnostic Test
Intervention description(s): Spirometry is a non-invasive means of measuring lung function: The participant is asked to take a deep breath and then exhale into the sensor as hard and as long as possible. Soft nose clips may be used to prevent air escaping through the nose. If the participant does not show a definitive diagnosis of asthma, a methacholine challenge test will be performed to elicit bronchoconstriction in participants. In methacholine challenge test, the participant breaths in standardized dose of nebulized methacholine again. Methacholine challenge test is widely accepted and standardized method for assisting the diagnosis of asthma and there will be no experimental altercation in the method methacholine challenge is performed.
Observational model: Case-Only
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Phase A of the study will be based on the survey of the general population (1-85 y/o) of
        two well-defined target areas and recruitment of those with a self-reported physician
        diagnosis of asthma. Phase B of the study is the retrospective elicitation of the health
        record of participants. In Phase C of the study builds upon the data of Phase A and B and
        other published studies to extrapolate the results to the Canadian population for the next
        10 years, as such it does not involve direct population sampling.