Epidemiology as a tool to assess the health effects of

climate changesAnnie J. Sasco, MD, DrPH

Epidemiology for Cancer Prevention, Team of HIV, Cancer and Global Health,

Inserm U 897René 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 principles

What are the domains of epidemiology and related population

health science ?• Descriptive epidemiology to see and describe the occurrence of

disease • 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 epidemiology

• Who?• When?• Where?• Why?• How?

• Or all the essential questions in life but here constrained to disease occurrence

Descriptive epidemiology

• Description of the state of health or disease of populations

• Globally and as a function of sex age country or place SES 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 co-

variables

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 modeling)

• Available on the WHO mortality data base

• 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 diagnosis

• 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) temperatures

• 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) temperatures

• Short-term effects of heat or cold waves Increased mortality and morbidity in

particular for cardio-vascular and respiratory diseases

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 mechanisms

Health effects of (extreme) temperatures – Epidemiological

monitoring• 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

groups• 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 events)

Extreme events – Epidemiological assessment

• Sudden and usually important peaks in immediate mortality and injuries, as well as some diseases in the following days or weeks

• 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 populations

• 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

assessment • 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 information

• 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 food

• 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 humans)

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 possible

• 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 change

• 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?