Week 3 Flashcards
(35 cards)
acute
- short term bursts of exposures (hours to days)
- often higher concentrations/doses
- may be followed immediately by symptoms or exacerbation of existing condition
chronic
- longer-term periods of exposure (years to lifetime)
- often lower concentrations/doses
- may be associated with onset of new disease (sometimes after long latency period)
form of exposure routes
Three routes of exposure
- dermal
- inhalation
- ingestion
- (also mother-> fetus)
Human barriers to the environment
- skin
- respiratory tract
- GI tract
Exposure route will influence both how you assess exposure and, potentially, how you intervene to reduce exposure
The environmental risk paradigm (exposure pathway - pollutants)
pollutant emissions -> movement of pollutants -> exposure -> dose -> effect
- pollutant emission, movement, exposure and dose are exposure assessment
what is exposure pathway?
The physical pathway a pollutant moves from the source to the subject
- how it moves through the environment (air, water) and how it enters the body (inhalation, ingestion, skin contact)
what is exposure route?
The way a substance enters the body
- inhalation, ingestion, or skin contact
Exposure pathways: where to intervene (3 intervention spots)
- at the source
- along the pathway
- at the household or individual
Air pollution example:
Pollution released into the environment (reduce emissions) -> movement of pollution (taller smoke stacks) -> exposure (air cleaners) -> (masks) -> dose -> effect (medical interventions)
How to reduce hazard exposure?
Produce less of that hazard
- less carbon emission (electrical cars, transit)
3 key ideas in exposure assessment
- concentrations vary in time
- temporal variation - concentrations vary from place to place
- spatial variation - people move around
- we want to know: what is the concentration where people are and when they are there?
Exposure assessment methods - direct methods
Includes:
- personal measurements
- biological markers (biomarkers)
Tradeoffs:
- can provide a better estimate of true exposure
- expensive and time-consuming
- high demand on participants
- often not feasible on a large scale
Exposure assessment methods - indirect methods
Includes:
- “area” measurements
- questionnaires
- models
Tradeoffs:
- may provide a poorer estimate of true exposure
- less expensive and time-consuming
- little to no participant demand
- can be applied to large populations
Direct methods: Biomarkers
Measure pollutants or metabolite in a biological material
- exhaled breath, urine, blood, teeth, hair
Tradeoffs:
- estimates dose and incorporates multiple routes of exposure
- can be intrusive, interpretation can be difficult
Indirect - Questionnaire-based exposure assessment made possible by
- knowledge of exposure: exposure of interest in this case was self-administered
- exposure of interest administered in consistent, quantifiable “units”
- stable exposures: smoking patterns don’t typically fluctuate widely over time; people tend to smoke in consistent patterns (amount, type)
Dr. Irving Selikoff (1915-1992)
- 1950s, several workers from a nearby asbestos factor sought treatment at Selikoff’s clinic
- he tried to get the workers medical records from their employer, but was denied
- working through the labor union, he was eventually able to obtain the workers records
epidemiology definition
The study of the distribution and determinants of disease in humans
3 key ideas in epidemiology
- not everyone who is exposed to a hazard will develop disease/illness from that exposure
- some kids who ate cold chicken did not get sick
- some people who smoke do not get lung cancer - Not every case of a disease/illness is the result of the exposure of interest
- some kids who did not eat cold chicken got sick
- some non-smokers develop lung cancer - Correlation is not the same as causation
- umbrellas don’t cause rain
- ash trays don’t cause lung cancer
Correlation does not equal causation
- the fact that A and B are correlated does not necessarily mean that A causes B or that B causes A
- causation can be difficult to prove, and observational studies alone generally cannot prove causality
-> experimental designs can provide stronger evidence of causality - the most compelling evidence often comes after replication and when the epidemiological and toxicological evidence converges
observational study designs
- cross-sectional
- case-control
- cohort
- time series
Experimental study designs
- RCT
- natural experiments
Experimental designs are uncommon in environmental and occupational health research
RCT - the ‘gold standard’ study design
- questions about external validity
- can be difficult to “blind” participants
- ethical concerns
-> usually we can only reduce exposure
-> should evaluate interventions and outcomes relevant to the population - usually evaluating exposure reductions at the individual or household level
-> generally not feasible to randomise cities, provinces, or countries to policy changes - generally not useful for evaluating diseases with long latency periods
-> acute or sub-chronic exposures, well defined exposure “window”
Cross-sectional study design
- “snapshot”
-> assess exposure and outcome at a single point in time - often a good place to start, “hypothesis-generating”
-> quick, inexpensive - not good for providing evidence of causality
-> temporal relationship between exposure and health outcomes is unknown
Cohort studies
- identify participants who do not have the disease of interest, observe them over time to assess new cases of the disease
Advantages:
- generally less susceptible to bias than cross-sectional or case-control
- temporal relationship between exposure and outcome is known
- can study rare exposures
Disadvantages:
- expensive and time-consuming (prospective cohort)
- not useful for studying rare diseases
case-control studies
- identify participants based on disease (Outcome), then determine who previously had the exposure
Advantages:
- often, relatively small sample sizes are adequate
- can study rare diseases
Disadvantages:
- exposure assessment is difficult (retrospective)
- not useful for studying rare exposures
odds ratio
the ratio of odds in favour of exposure among the cases to the odds in favour of exposure among the non-cases
