epidemiologia ambiental classroom 2012 d

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

[email protected]

ext: 1441

1

Environmental Epidemiology
mailto:[email protected]:[email protected]


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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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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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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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Design

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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.htm


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Assessment of exposure


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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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


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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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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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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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.pdf


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Choose a study design

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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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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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Statistical modeling

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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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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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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


Main objective is to

assess association

between asthma

onset in children and

traffic related air

pollution.

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.pdf


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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


http://oem.bmj.com/content/61/9/773.full.pdf+htmlhttp://oem.bmj.com/content/61/9/773.full.pdf+html


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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.


Assess association

between outdoor air

pollution and low

birth weight.http://oem.bmj.com/content/56/8/539.full.pdf

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.pdf


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GISA project

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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).

http://www.biomedcentral.com/content/pdf/1471-2458-10-613.pdfhttp://www.biomedcentral.com/content/pdf/1471-2458-10-613.pdf


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GISA project

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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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GISA project

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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



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GISA project

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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.

epidemiologia ambiental classroom 2012 d

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