Epidemiology as a tool to
assess the health effects of
climate changes
Annie J. Sasco, MD, DrPH
Epidemiology for Cancer Prevention,
Team of HIV, Cancer and Global Health,
Inserm U 897
René Labusquière Center
Bordeaux Segalen University, France
The opinions expressed in this talk are solely those of the speaker and should
not be taken as official position of the Inserm or the University
What is epidemiology ?
• Epidemiology is the science of the
occurrence of disease
• Its goals are (or should be) to:
- see and describe
- understand
- and last but not least allow to act
based on knowledge and ethical
What are the domains of
epidemiology and related population
health science ?
• Descriptive epidemiology
to see and describe the occurrence of
• Etiologic epidemiology
to discover and understand the causes
of the occurrence of disease
• Prevention of disease: primary,
secondary, tertiary
Alternative ways of looking at the
domains of epidemiology
Based on origin of study subjects
• Population based epidemiology
general population subjects
• Clinical epidemiology
patients exclusively
• Comparative epidemiology
humans and animals
• Evaluative epidemiology
methods of intervention
Questions to be answered by
• Or all the essential questions in life but
here constrained to disease occurrence
Descriptive epidemiology
• Description of the state of health or disease of
• Globally and as a function of
country or place
race or pertinent cultural background
many other determinants (if available…)
• Two sources of data
mortality / morbidity
Mortality data
• The most widely available, yet far from being
exhaustively universal
• Varying quality depending on
mode of certification of death (by whom?
how assessed?)
mode of registration of death (fact of death,
cause of death, level of anonymity)
legislation (access in particular)
usually extremely poor availability of covariables
Mortality data and estimates
• Real data for many but not all countries
(in particular for a national coverage)
• Estimates for other countries (based on
ad hoc studies, extrapolations and
• Available on the WHO mortality data
• Not really useful for non lethal diseases
or poorly diagnosed ones
Morbidity data
• Even less available than mortality data
• For a few diseases in some places,
based on disease registries
• Varying quality (mode of assessment,
reporting, classification) often linked to
the type of disease and the place of
• Only possibility to quantify the disease
when it is non lethal
Morbidity data and estimates
• No country has an exhaustive coverage
of all diseases at a national level
• Estimation from ad hoc studies, use of
routine data bases, surveillance
networks, extrapolations and modeling
Health effects of climate change
As listed in the US EPA and other reports
• Direct temperature effects
• Extreme events
• Climate-sensitive diseases
• Air quality
• Other health linkages
To which I shall add other effects, although
some of them are linked to the above
mentioned ones
Health effects of (extreme)
• Effects of hot or cold temperatures
Increased mortality associated with low
and high temperatures all over the
world, but usual temperature
modulates the heat threshold
Clearer for cardio-vascular and
respiratory mortality
Effects more marked in low- and
middle-income countries
Health effects of (extreme)
• Short-term effects of heat or cold waves
Increased mortality and morbidity in
particular for cardio-vascular and respiratory
Affecting the most vulnerable populations
(aged, poor, sick)
• Long term effects of climate change
Isolated effect of temperature not yet really
known but impact through other
Health effects of (extreme)
temperatures – Epidemiological
• Routine health statistics on mortality (and if
available in a few places on morbidity)
• Use of numbers and rates (for comparisons
in time and space), taking into account
baseline values
• For small effects in particular, sensitivity of
the results based on statistical approach
being used as well as unit of analysis or
choice of thresholds and latency
Extreme events
• Various climatic or linked to climatic events
floods, hurricanes, fires, etc
• Common outcome: increased mortality and injuries,
as well as stress related events
most marked in the poorest countries or population
• Changes in behaviors and conditions of living with
their health consequences (crowding, poor hygiene)
• Other outcomes dependant on the type of the event:
water-borne diseases if flood or extreme
precipitations, respiratory and ocular effects linked
to dust and particulate matters for fires (and volcanic
Extreme events –
Epidemiological assessment
• Sudden and usually important peaks in
immediate mortality and injuries, as well as
some diseases in the following days or
• Clear effects even in the absence of precise
statistics but may be under-estimated or
over-estimated for groups poorly accounted
for or voluntarily ignored in census statistics
(migrant populations, illegal aliens)
Climate refugees and similar
• Displaced populations
increase in water level on low lands
impact of droughts
• Will change way of life, social habits, food and water
availability, conditions of living, work and
employment possibilities, cultural context
• Health effects will be specific for each of the above
life modifications, affecting to a larger extent the
least favored groups and the most susceptible
subjects and clearer in the poorest, most
overcrowded countries
• Other health effects will be linked to the stress
experienced by the persons with increases in
unwanted psychological distress and conditions
Climate refugees and similar
populations – Epidemiological
• Most difficult to assess
• Will be dependant on type of data collected
if no data registered on place of origin,
reason for moving, no routine monitoring will
be possible
only ad hoc studies will bring about some
• Need for a climate refugee observatory or
rather a network of surveillance centers
Air and related pollution
• Agents of interest
- ozone: thinner ozone layer leading to increased
solar exposure with resulting higher risk of skin
cancer and in particular melanoma, most marked in
genetically predisposed populations (fair skinned)
higher ground level ozone: smog will
increase respiratory unwanted effects with higher
severity of asthma, and other chronic long term
respiratory diseases
- particulate matters, nitrogen oxides, volatile organic
compounds. Role of PM depending on size in
chronic respiratory diseases, cardiac diseases and
cancer of the lung
Water and soil pollution
• Will affect quality of drinking water and
• Agents of interests: water-borne
infectious agents, pollutants (including
residues from pesticides and fertilizers
if poorer quality of soil)
Air, water and soil pollution –
Epidemiological assessment
• Trends in the occurrence of pertinent
diseases in terms of occurrence,
morbidity and mortality based on
routine statistics, provided their quality
is good enough
• Specific comparative studies (different
places and populations, including non
Climate-sensitive diseases
• Traditionally the South has been the place for
diseases mostly linked to biological agents
viruses, bacteria and parasites
• The vast majority of tropical diseases are
linked to infectious agents and many of them
are either water borne or vector borne
diseases (mostly mosquitoes and ticks)
• With warmer climates extending to parts of
the North, the geography of these diseases is
going to change and expand
Climate-sensitive diseases of
specific interest
• Malaria and cholera may be the 2 most important
ones in terms of frequency
• Also an interest for dengue, yellow fever, various
encephalitis, chikungunya, West Nile fever, tularemia
• Some of these diseases are zoonoses
• All are preventable, including for some of them
through vaccines
• Level of curability varies
• Need to educate physicians from the North about
these diseases to avoid misdiagnosis, in particular
in non travelers
Carcinogenic biological agents
• Viruses
Human papilloma viruses (HPV)
Human immunodeficiency viruses (HIV)
Hepatitis B and C viruses (HBV, HCV)
Epstein-Barr virus (EBV)
Human herpes virus 8 (HHV 8)
Human T cell leukemia viruses (HTLV)
• Bacteria
helicobacter pylori
• Parasites
schistosoma, opisthorchis viverrini
Climate-sensitive diseases –
Epidemiological surveillance
• Trends in the occurrence of pertinent
diseases in terms of occurrence,
morbidity and mortality based on
routine statistics. As this will concern
countries of the North, it should be
• Need for serological population
surveys to assess the extent of
infection, even subclinical
In conclusion
• Epidemiology will have an important role to play in
the monitoring of the impact on health of climatic
• Yet, tools will have to be adapted and most
importantly data sources have to be improved in
terms of both quality, coverage and availability
• Background levels of all expected outcomes should
be obtained as soon as possible to permit
subsequent evaluation of trends
• Specific observatories should be set up
• An open mind should be kept for as yet unexpected
outcomes and long term monitoring, including of
seemingly acute events
Thank you for your attention
Any questions?