Epidemiology and Public HealthEpidemiology and Public Health

This presentationThis presentation

• Definition of epidemiology

• Beginnings of epidemiology

• Objectives/types of epidemiology

• Roles of an epidemiologist

• Examples

• Importance of communications

Definition of Epidemiology…Definition of Epidemiology…

Student“ The worst course at medical school ”

Clinicien“The science of making obscure what is already

simple and clear ”

Average citizen“The study of skin disease ”

Definition of epidemiologyDefinition of epidemiology

The study of the distribution and determinants of the health status or events in the population and its application to control public health problems

Source: Last 2001. A Dictionary of Epidemiology: 4th Edition. Oxford University Press: New York.

Another definition of Another definition of EpidemiologyEpidemiology

“A tool for action which promotes and protects the health of a population, based in science, causal reasoning, and common sense...”

The beginning of epidemiology The beginning of epidemiology and public health…and public health…

• Cholera epidemics in England – cause was unknown– 1831 : 22 000 deaths – 1848 : 52 000 deaths – 1853: 10,600 deaths

– 1854: Epidemic of cholera in London (Soho district)

• John Snow (1813-1858): physician, anesthesiologist, and “Father of Epidemiology” – Mapping of cases according to place of residence and work

Cont…Cont…

The distribution of cases led Snow to think that the water from pump A was causing the cholera

– Most of the cases had drunk water from pump A

– None of the workers at the nearby pub or workhouse had fallen sick (and had not drunk water from pump A)

– Certains cases outside of the zone had drunk water from pump A

The end…The end…

• Snow removed the handle of pump A and the epidemic stopped immediately

• Snow did subsequent studies to confirm his hypothesis of water as a vehicle for cholera transmission

And the pump

without the handle

is still there!!!!

Objective of epidemiology in Objective of epidemiology in public healthpublic health

• Determine the burden and trend of disease

• Identify the cause and mode of transmission

• Identify risk factors

• Guide public health measures and evaluate their impact

• Guide communications

The The ““epidemiologic triangleepidemiologic triangle””Factors that can affect the occurrence of diseaseFactors that can affect the occurrence of disease

Host

Agent

Environment

• Observational– Descriptive (person, place, time, clinical features)– Analytique (makes a comparison)

• Case control• Cohort• Cross-sectional

• Experimental (makes a comparison, assigns controls)

• Randomized, controlled• Non-randomized, controlled

Types of EpidemiologyTypes of Epidemiology

Descriptive Epidemiology Analytic Epidemiology

Search for clues Clues available

Formulate hypotheses Test hypotheses

No comparison group Comparison group

Answers: who, what, when, where, how much

Answers: How, why

Observational epidemiology

Principle activities of a field epidemiologistPrinciple activities of a field epidemiologist• Describe an event in terms of:

– Person Who ?– Place Where?– Time When?– How much Incidence/prevelence?– What Clinical features?

• Analyze the association between an event (illness, death) et its determinants (risk factors) – make comparisons

• Recommend preventive actions and control measures

• Evaluate impact or changing epidemiology

0

1

2

3

1883 1893 1903 1913 1923 1933 1943 1953 1963 1973 1983 1993 2003

Epidemicity*

1: epidemic, 2: probable pandemic, 3: pandemicPotter, C.W: Textbook of Influenza by Nichols, Webster, Hay, Blackwell Science 1998

30 years 10 10

39 years?

Recorded Influenza Pandemics

10 20

2006

Human Avian Influenza A/H5N1 CasesHuman Avian Influenza A/H5N1 Cases

Confirmed cases of Confirmed cases of Human AI Human AI H5N1H5N1Dec 2003 to 29 May Dec 2003 to 29 May 20062006

Country Cases Deaths

Azerbaijan 8 5

Cambodia 6 6

China 18 12

Djibouti 1 0

Egypt 14 6

Indonesia 48 36

Iraq 2 2

Thailand 22 14

Turkey 12 4

Viet Nam 93 42

Total 224 127

Over-all CFR: 57 %

Understanding the natural history of diseaseUnderstanding the natural history of disease

Expanding host range for Influenza A/H5N1

Owston Palm Civet, Domestic cat/feral cat, Stone marten, Cynomolgus macques, Ferret, New Zealand white rabbit, Leopard, Tiger, Rat, PigWood duck, Brazillian teal, Bahama pintail, Chestnut-breasted teal, Argentine shoveller, Domestic duck, Chiloe wigeon, Gadwall, Puna teal, Domestic goose, Lesser white-fronted goose, Bar-headed goose, Common pochard, Tufted duck, Canada goose, Red-breasted goose, Ringed teal, Manned wood-duck, Coscoroba swan, Black swan, Whooper Swan, Black-necked swan, Mute swan, White-faced whistling-duck, Smew/Common merganser, Hawaiian goose, Rosybill pochard duck, Red-crested pochard, Ruddy shelduck, Laughing gull, Brown-headed gull, Great black-headed gull, Black-headed gull, Green sandpiper, Asian open-billed stork, Grey heron, Great blue heron, Chinese pond heron, Little egret, Feral pigeon, Little cuckoo dove, Red-collared dove, Northern goshawk, Buzzard, Saker falcon, Peregrine falcon, Grey-headed fish-eagle, Serpent eagle, Crested hawk-eagle, Chukar partridge, Bobwhite quail, Japanese quail, domestic chicken, Kalij pheasant, Turkey, Pearl guineafowl, White Indian peafowl, Ring-necked pheasant, Brown (red-legged) crake, Coot, Common moorhen, Sultan (Purple swamphen), Crested mynah, House finch, Oriental magpie robin, Jungle crow, House crow, Black drongo, Hill mynah, Red-billed leiothrix, Scaly-breasted munia, Black-naped oriole, House sparrow, Eurasian tree-sparrow, Korean magpie, European starling, Zebra finch, Japanese white-eye, Great cormorant, Little cormorant, Greater flamingo, Great crested grebe, Budgerigar, Spot-bellied eagle-owl, Buffy fish-owl, Brown fish-owl, Spotted wood-owl, Emu

(10 mammalian and 88 avian species)

Influenza A/H5N1Influenza A/H5N1Likely Source of Exposure, IndonesiaLikely Source of Exposure, Indonesia

(data up to April 2006)(data up to April 2006)

Direct Exposure, 8

Indirect Exposure, 17

Fertiliser, 2

Inconclusive, 5

Direct ExposureIndirect ExposureFertiliserInconclusive

Prerequisites of a PandemicPrerequisites of a Pandemic• A novel influenza virus must emerge to which the

general population has little or no immunity and for which there is no effective vaccine

?

• The new virus must be able to replicate in humans and cause disease

• The new virus must be efficiently transmitted from one human to another causing global spread of disease

Clusters in IndonesiaClusters in IndonesiaCluster Cases Fatal Source H2H Type of cluster

1 3 (1 confirmed, 1 pending, 1 suspect)

3 Inconclusive Cannot be ruled out

Blood-related family

2 2 (2 confirmed) 1 Fertilizer Cannot be ruled out

Blood-related family

3 3 (3 confirmed) 0 Direct (sick chicken)

Unlikely Blood-related family

4 2 (2 confirmed) 1 Exposure (sick chicken)

Unlikely Blood-related family

5 4 (2 confirmed, 2 suspect)

2 Direct (sick chicken)

Unlikely Blood-related family

What does the epidemiology tell us about the What does the epidemiology tell us about the public health risk of an influenza pandemic?public health risk of an influenza pandemic?

• Current extent and frequency of H5N1 outbreaks among poultry is unprecedented

• Host range and geographic range is expanding

• H5N1 is entrenched in poultry in Asia, where humans and poultry live in close contact

• Clusters to date appear to be in blood relatives suggesting some genetic susceptibility factor

• High CFR in humans who contract the illness

• Efficient human-to-human transmission has not yet occurred

• There is still a “window” of opportunity to prepare, but the length of the window is unknown

Excellent epidemiology alone rarely leads to Excellent epidemiology alone rarely leads to improvements in public healthimprovements in public health

Mark White, 2002

Roles of the 21st Century epidemiologist Roles of the 21st Century epidemiologist working in public healthworking in public health

• To transform data into meaningful information to guide public health measures and maintain support for the measures

• To get the information to those who can affect change

• To communicate (rather than just disseminate) information

• To get involved in “risk communication”

• To work with various partners and across sectors to plan and implement effective strategies

Working across sectorsWorking across sectorsPandemic Preparedeness PlansPandemic Preparedeness Plans

• Animal Health Services• Biosecurity• Human Public Health• Continuity of Governance and

Rule of Law• Sustaining Economic and Social

Systems• Assessing vulnerability and

providing humanitarian relief

Animal

Health

Humanitarian& Relief

Coordination & Communication

Human

Health

Economy& Society

Governance& Rule of Law

PAHO

Documenting impact!Documenting impact!Monitoring progress over time towards measles eliminationMonitoring progress over time towards measles elimination

Reported measles cases by month, Cuba, 1971-1998Reported measles cases by month, Cuba, 1971-1998

Source: Ministry of Health, Cuba

1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

Month and Year

0

1

2

3

4

5

6Reported cases (thousands)

0

20

40

60

80

100MMR vaccine coverage (%)

Catch-up Follow-up

Keep-up

vaccinationcampaign

vaccinationcampaign

vaccination

Documenting a changing epidemiologyDocumenting a changing epidemiology

Cases of laboratory confirmed malaria and Cases of laboratory confirmed malaria and proportion due to proportion due to P. falciparum, 1992-96P. falciparum, 1992-96

0

100

200

300

400

500

600

1992 1993 1994 1995 1996

Others

Faciparum

Documenting a changing epidemiologyDocumenting a changing epidemiologyIncidence rate of pertussis notifications by age and year of onset,

Australia, 1991-97

Cas

es /1

00 0

00 p

opul

atio

n

Year

Source: Australia CDI (21)23, 25 December 1997

Mortality from tractor accidents by age Mortality from tractor accidents by age group. Georgia, 1971-81group. Georgia, 1971-81

Analytic epidemiologyAnalytic epidemiologyCohort StudiesCohort Studies

Disease No Disease

StudyPopulation

Exposed Non-exposed

No DiseaseDisease

Exposure isself selected

Follow throughtime

Source: Public Health Information Network (PHIN) Series I. North Carolina Center for Disease Preparedness and Virginia Department of Health

Analytic epidemiologyAnalytic epidemiologyCase-Control StudiesCase-Control Studies

Had Exposure No Exposure

StudyPopulation

Cases Controls

No ExposureHad Exposure

Source: Public Health Information Network (PHIN) Series I. North Carolina Center for Disease Preparedness and Virginia Department of Health

Table from a case control studyTable from a case control study

Table 5. Association between exposures and campylobacteriosis in case-control

study, Oslo, Norway, 1998. Univariate, matched analysis.

Exposure Cases Controls Odds 95% conf.

ratio interval

Eaten at pizza restaurant 9/37 12/70 1.8 0.62 - 5.0

Eaten at party 10/36 9/74 3.2 0.97 - 11

Eaten foods from deli 23/37 42/74 1.2 0.56 - 2.7

Eaten unpeeled fruits 19/37 54/74 0.27 0.10 - 0.78

Close contact with a case 7/35 2/72 13 1.5 - 110

Drank >4 glas of water per day 21/37 33/74 1.7 0.73 - 3.9

Customer of water company B 27/37 33/74 4.0 1.3 - 7.3

Source: Preben Aavitsland, tables, graphs, diagrams, EPIET training

• To maintain public confidence and trust

• not just information dissemination– Instead sharing the meaning of the information– Defining/understanding the audience– Selecting the best channels– Marketing the information

• a two-way process– “Communication surveillance” – listening to the concerns of the community

• risk communication/social mobilization• Communicating to promote behavior change that reduces risk

Tasks of the 21st Century epidemiologist Tasks of the 21st Century epidemiologist working in public healthworking in public health

““Communications”Communications”

Epidemiology and Public HealthEpidemiology and Public HealthCommunicationsCommunications

Avian influenza in AzerbaijanAvian influenza in Azerbaijan

“During the field visits to Daikyand settlement, it emerged that risk perception at community level was limited and that local residents persistently denied avian influenza as the cause of the illnesses and deaths of affected community members……

…..Unfortunately, this difficulty in communication hampered the implementation of control measures as well as the investigation of the source of infection.

Local residents did not believe that avian influenza had been diagnosed and were reluctant to provide further information that could negatively impact themselves (e.g. admitting to having de-feathered wild swans or having had contact with wild birds).”

Human avian influenza in Azerbaijan, February–March 2006WEEKLY EPIDEMIOLOGICAL RECORD, NO. 18, 5 MAY 2006

Uptake of the MMR vaccine in the UK since 1992 (source: MMR Decision Making Study, Durham University)

Wakefield study published

Maintaining public confidence Maintaining public confidence in public health measuresin public health measures

“We had to close our school, our playroom and open special wards for measles. 11 children were in ITU and 7 were ventilated…

…This was a pretty serious toll of preventable disease that children had to suffer because parents had not had their children vaccinated in sufficient numbers.”

By 2000, vaccination coverage had dropped to 60%. There were a total of 1603 cases. 600 were hospitalized.

Naomi Pop was too young to be vaccinated when she fell sick.

She was one of 3 children who died.

Understand the public

Risk communicationsRisk communications

Announce early

Outbreak Communications

Be transparent

Outbreak Communications

“In today’s globalized, wired world, information is almost impossible to keep hidden from the public. Eventually, the public health issue will be revealed.”

Communications

Epidemiology and Public HealthEpidemiology and Public HealthMeans working as a team!Means working as a team!

• Health/Agricultural Officials• Lab Workers• Clinicians• Policy makers• Media• Community & local leaders• Advocacy Groups