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7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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Seminar on Environmental Epidemiology
Integrated Master in Environmental Engineering
Instituto Superior Tcnico2nd Semester 2011/2012
Manuel Castro Ribeiro
ext: 1441
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Environmental Epidemiology
mailto:[email protected]:[email protected]7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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Topics
2IST-UTL, March 6th 2012
Introduction- What is environmental epidemiology
Concepts- Design, outcome, exposure
Methods- Measures of exposure, disease
Some case studies- Air quality
Introduction Concepts Methods Case studies
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Milestones
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Introduction Concepts Methods Case studies
Hippocrates (460-370 BC) On Airs, Waters, and Places. Connection between
different diseases occurring at different places.
Ramazzini (1633-1714) The disease of workers. Occupational diseases
(connection between adverse health effects on occupations exposed to dust,chemicals, metals.
Richard Doll (1912-2005) Smoking and carcinoma of the lung (BMJ, 1950).
Established link between smoking tobacco and lung cancer
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Environmental epidemiology
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Introduction Concepts Methods Case studies
Epidemiology - Study of the determinants of health-related states or events, in time,
space and populations (Last).
Environmental Epidemiology - Study of the determinants of health-related states or
events that are influenced by environment, in time, space and populations.
Environment- All that is external to human host. Environment can be divided into
biological, physical, chemical, social, cultural (Last, 1995).
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Systemic approach
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Introduction Concepts Methods Case studies
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Design
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Introduction Concepts Methods Case studies
Whoshould be studied? population at risk? Who should be selected?
Where should the study to take place? Should geographical position, altitude,
meteorology, etc., be taken into account in selecting a locality? Are there existing
monitoring stations or sets of data relating to the environmental factors in question?
Whenshould the study be carried out? Are seasonal effects likely to be important?
Is the available time-span long enough to provide a satisfactory estimate of long-
term exposures? Should exposures be averaged over months or years, or are short-
term peaks relevant in some cases?
Whatshould be measured? Single pathway (for example, via inhalation) or several
ways of entry to be considered simultaneously? How are effects on health to be
assessed?
In International programme on chemical safety Guidelines on studies in environmental epidemiology
Url: http://www.inchem.org/documents/ehc/ehc/ehc27.htm#PartNumber:1
http://www.inchem.org/documents/ehc/ehc/ehc27.htmhttp://www.inchem.org/documents/ehc/ehc/ehc27.htm7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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Assessment of exposure
Introduction Concepts Methods Case studies
Environmental Exposure- Opportunity to absorb into the body as a result of coming
into contact with a environmental factor. To assess exposure we can use direct or
indirect methods.
Direct methodsPersonal monitors- devices used by individuals (workplace, home) that collect
quantitative measures of personal exposure to environmental pollutants (ex:
dosimeter to estimate total exposure to radiation in workplace).
Biologic markers- Key molecular or cellular events that link a specific environmental
exposure to a health outcome (ex: maternal urinary iodine to prevent damagingconsequences on fetal and infant development).
Indirect methods
Combine concentrations measured in environment (through environmental
monitoring) to which people may be exposed, with information on peoples activities
collected through questionnaires or (time activity) diaries.
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Environmental monitoring
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Introduction Concepts Methods Case studies
Assessment of exposure (quantitative terms)
Environmental monitoring , systematic collection of environmental samples for
analysis of pollutant concentrations" (Berlin et al., 1979).
Berlin, A.; Wolff, A.H. and Hasegawa, Y., ed. (1979) The use of biological specimens for the assessment of human exposure to
environmental pollutants. In: Proceedings of the International Workshop CEC-WHO-EPA, 1977, The Hague, Nijhoff, 368 pp.
- What pollutant(s) to study?- How long and how often should samples be taken?- Where should samples be drawn from, or instruments located?- What quality of data is needed?- Which instruments or analytical techniques should be used?
The quality is determined both by sampling and byanalytical procedures. If the quality of exposureassessment is below a certain minimum, the dataobtained may be valueless.
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Assessment of outcome
Introduction Concepts Methods Case studies
Outcome- Health-related state or event under investigation.
Clinical data- information collected by health professionals on diagnosis, treatment
and care of each patients. Outcome definition should be clear and specific.
Diagnostic tests to predict the presence of an outcome: sensitivity(proportion ofpatients with outcome and positive test) and specificity(proportion of patients without
outcome and negative test). Use of standard clinical criteria and case definition to
reduce misclassification and to reduce bias.
Aggregated health data- data concerning diagnosis, treatment and care of
populations (grouped data) usually published by national statistical institutes orhealth observatories
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Introduction Concepts Methods Case studies
Conceptual risk model
True intake may differ considerably from the levels of exposure calculated from
concentrations in ambient air, food, or drinking-water.
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Introduction Concepts Methods Case studies
Induction and Latency
Induction and latency periods can take hours (ex: sunburn) or years (ex: cancers)
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Methods in epidemiology
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Introduction Concepts Methods Case studies
Study design (or study protocol)- formal approach of scientific investigation. It guides
researcher along the path of systematically collecting, analyzing and interpreting
results.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1519688/pdf/envhper00381-0018.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1519688/pdf/envhper00381-0018.pdfhttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC1519688/pdf/envhper00381-0018.pdf7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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Choose a study design
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Introduction Concepts Methods Case studies
Descriptive studiesFirst step in epidemiology research. Focus on description of health event in time,
place and population. Can provide clues on etiologic relation between environment
and disease (just hypothesis).
Analytical studies
Adequate to identify etiologic relation between environment and disease.
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Basic designs
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Introduction Concepts Methods Case studies
Cohort study- exposure status is measured for all persons at beginning of follow
up and during follow up. Usually prospective. There is no temporal ambiguity
concerning exposure.
Case-control (CC)- retrospective study, with controls (healthy persons) and cases
(persons with disease) selected at beginning of study. Exposure are measured
retrospectively. Very useful for rare diseases, specially if latent periods are long.
Cross-sectional- all variables measured at a point in time (snapshot). Only suited
to measure prevalence (nr of patients at a specific snapshot of time). No follow up
is needed, less time consuming and costly (than some other types of study).Important for planning health services and policy analysis.
Ecological- The unit of observation is a group and not a person. Official statistics
(publish aggregated data) can provide data for analysis. Suppress the need to
collect data individually. Easy to study large populations. Exposure of individuals
are not linked to disease occurrence of those individuals.
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Basic designs
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Introduction Concepts Methods Case studies
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Statistical modeling
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Introduction Concepts Methods Case studies
Applied in all designs. Instruments suited to measure exposure, outcome and
associations between exposure and outcome.
(Ill focus on outcome measures)
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Statistical modeling
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Introduction Concepts Methods Case studies
Basic statistics to deal with epidemiological data
They can be descriptive or they can measure strength of association between
outcome and some environmental factor. Some of the more important
epidemiological indicators measured.
Incidence - Nr of newly diagnosed cases during a specific time period.
Prevalence - Nr new and pre-existing disease cases alive on a certain date.
Risk ratio (or Relative risk) - Measures excess of disease occurrence
Odds ratio - Measures excess of disease occurrence.
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Cause-effect
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Introduction Concepts Methods Case studies
Several criteria exist
Strength of association the relationship must be clear.
Consistency observation of the association must be repeatable in different
populations at different times.
Temporality the cause must precede the effect.
Plausibility the explanation must make sense biologically.
Biological gradient there must be a dose-response relationship.
Adapted from The Bradford-Hill criteria (J Roy Soc Med 1965:58:295-300)
I t d ti C t M th d C t di
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Cohort
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217 children (10-18 yrs) with no reported asthma selected from ongoing study, were
followed for 8 years (annual reports). Passive samplers for NO2 placed outside
residences of children (2 weeks on winter and summer campaigns). In the end of
follow up period, 30 cases of asthma have been reported. Several covariates havebeen collected (socioeconomic and meteorological variables).
Hazard ratio (a specific type of Relative risk) was 1.29 (1.07-1.56) for an average
increase of 6.2 ppb in annual residential NO2. This risk suggests that air pollution
contributes to new-onset asthma.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569108/pdf/ehp-116-1433.pdf
Introduction Concepts Methods Case studies
Main objective is to
assess association
between asthma
onset in children and
traffic related air
pollution.
I t d ti C t M th d C t di
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569108/pdf/ehp-116-1433.pdfhttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569108/pdf/ehp-116-1433.pdf7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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Case-Control
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Main objective is to
assess association
between exposure to
hydrocarbons and
childhood leukemia.
Hospital based, selected 280 cases (0-14 yrs at time of diagnosis) diagnosed
between 1995-1999 and 285 controls (hospitalized for acute pathologies, traumatic,
orthopedic, non-cancer disease) matched on age, sex and ethnicity. Standardized
questionnaire on past history of exposure to hydrocarbons, neighbouring business,
heavy traffic in vicinity of children's homes, parents occupations, pregnancy
exposure to solvents.
No clear association between maternal occupation exposure to hydrocarbons during
pregnancy and leukemia or residential traffic density and leukemia. Associations
were found for dwellings near petrol stations, repair garage during childhood and risk
of childhood leukemia (OR 4, 1.5, 10.3).
http://oem.bmj.com/content/61/9/773.full.pdf+html
Introduction Concepts Methods Case studies
I t d ti C t M th d C t di
http://oem.bmj.com/content/61/9/773.full.pdf+htmlhttp://oem.bmj.com/content/61/9/773.full.pdf+html7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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Cross-sectional
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Parents of farmers children and a random sample of non-farmers children
completed a questionnaire on asthma, hay fever, atopic eczema diagnosed by doctor
and exposure to farming environment during pregnancy and early life (n=812).
Exposure to stables and farm milk for children
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Ecological
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Unit of analysis is district . Air quality monitoring stations
for TSP, SO2 and Nox. Annual average concentrations by
district.
Pregnancy outcomes provided by Czech Statistical Office(outcomes). Data on several socio-economic factors were
collected (confounding factors).
Birth weight was associated with SO2 (OR 1.1; 1.02,1.17).
Association between air pollution and birth weight requires
further investigation.
Introduction Concepts Methods Case studies
Assess association
between outdoor air
pollution and low
birth weight.http://oem.bmj.com/content/56/8/539.full.pdf
Introduction Concepts Methods Case studies
http://oem.bmj.com/content/56/8/539.full.pdfhttp://oem.bmj.com/content/56/8/539.full.pdfhttp://oem.bmj.com/content/56/8/539.full.pdfhttp://oem.bmj.com/content/56/8/539.full.pdf7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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GISA project
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Introduction Concepts Methods Case studies
Assess associations between
outdoor air quality and birth
outcomes in Alentejo Litoral
region?
http://www.biomedcentral.com/content/pdf/1471-2458-10-613.pdf
A retrospective cohort study, participants are all mothers that had one birth between
2007-2010 in Alentejo Litoral region, that accept to participate. Lichen biomonitoring
program is used for ecologic assignment of personal exposure (at same sampling
sites we also set four campaigns with passive samplers for SO2, NOx and O3 to
validate lichen data).
Questionnaire on socioeconomic and demographic, clinical data, past obstetric
history, place of residence, place of work, mothers occupation during pregnancy,smoking habits, diet, housing conditions (n=1655).
Introduction Concepts Methods Case studies
http://www.biomedcentral.com/content/pdf/1471-2458-10-613.pdfhttp://www.biomedcentral.com/content/pdf/1471-2458-10-613.pdf7/31/2019 Epidemiologia Ambiental ClassRoom 2012 d
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GISA project
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Introduction Concepts Methods Case studies
Research team
1 meteorologist
1 statistician
1 sociologists
3 biologists
6 engineers
8 doctors20 nurses
Ethical issues- data onhealth is sensitive. A written
informed consent must be
fullfilled by each participant
(http://www.cnpd.pt/). Also
an ethical committee must
read and agree with the
research(http://www.cnecv.pt/)
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Introduction Concepts Methods Case studies
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GISA project
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Introduction Concepts Methods Case studies
0.0%
10.0%
20.0%
0 50 100
%BPN
Biodiversidade liqunica mdia
=-0,615
10.9%8.6%
8.2%
6.9%
6.8%
6.5%
5.7%
3.2%
Sines*Alentejo 2009
*Portugal 2009
Alentejo Litoral
Grndola
Odemira
Stgo Cacm
Alccer SalBaixo peso nascena
Introduction Concepts Methods Case studies
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GISA project
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Introduction Concepts Methods Case studies
Other covariates that are associated with an increased risk of low birth weight:
Pregnancies followed in Sines primary health centre
Low weight gain during pregnancy
Null parity
Preterm birth
Previous preterm birth
Previous low birth
Intrauterine growth retardation
Preeclampsia
Several multivariate models (glm) are being fitted and we are performing several
tests to identify (and remove) confounders and effect modifiers.