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Lecture notes (overall summary of all classes) Introduction to epidemiology and public health (HNH24806)
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Introduction Epidemiology and public healthWEEK 1
Epidemiology = the study of what is upon the people
Questions: What, who where, when why
Important people: James Lind, Edward Jenner, Ignaz Semmelweis (ontdekker dat je handen moet
wassen), John Snow (cholera occurance, via water supply in households)
- Epidemiology has developed from social medicine and statistics.
Can be characterized by:
- Population thinking
- Group comparisons
Hippocrates: The first who suggested that the development of human disease might be related to
the external as well as the personal environment of an individual.
- Endemics: diseases usually found in some places, but not in others
- Epidemics: Diseases that are seen at some times, but not others
Roots of epidemiology:
- Acute disease investigation
- Medicine
- Statistics
- Social science
- Computer science
- Managerial science
- Genomics
Purpose of epidemiology: The prevention of disease and the promotion of health
History:
Pre-formal 1662-1990 (John Graunt (schreef boek), William Farr, John Snow)
- Epidemiologists wisten zelf ook nog niet goed wat epidemiologie inhield
- infectious diseases, nutritional deficiences
- Staten begonnen aantal inwoners & dodenaantal te tellen
- Dokters zagen dat ziektes niet gelijkmatig verspreidden over populaties
- Social drive om uit te zoeken waardoord e ziektes veroorzaakt werden en behandeld konden
worden: Hygiene & Sanitation
- People travelled all over the world
- Disease imported, exported, pueperal, fever, cholera
- Group thinking started to emerge: ziektes blijven niet bij 1 persoon (infectious diseases)
- Louis wordt gezien als de eerste klinische epidemioloog: hij ontdekte population thinking and group
thinking.
Early epidemiology 1900-1940
- Transition of acute infectious to chronic disease
- Interdisciplinary nature of epidemiology became more on the foreground
- Eerste epidemiology docent in Londen (heette Greenwood)
- Focus lag op non-communicable diseases (pellagra, vitamins)
Classical epidemiology 1940-1980
- chronic diseases
,- Large scale epidemiological studies started
- New epi-methods, study design
- Became established academic field in US/UK
- TBC, Tobacco smoke
→ Focused on infectious diseases & chronic diseases (any disease). And the controversy about the
health effects of tobacco smoke
- Methodology. Case-control, cohort, ecological, RCT, stratification & regression.
Definition of epidemiology: The study of the distribution and determants of health related states of
events in specific populations, and the application of this study to control health problems.
Modern epidemiology 1980-now
- All these different study design find a theoretical basis in RCT (random controlled trial),
differentiation of expertise
→ Prevention strategies (prim, sec, tertiary)
- Intervention trials
Definition of epidemiology: The ultimate goal of most epidemiologic research is the elaboration of
causes that can explain patterns of disease occurance.
Any disease → all aspects of human health
Measures of frequency:
1. Prevalence: hoevaak het voorkomt in de populatie op een bepaalde tijd
Prevalence proportion= aantal zieke mensen / totaal aantal mensen
point prevalence: Number of adults with an episode of flu on a specific point.
Period prevalence: Number of adults with an episode of flu in a specific time period.
2. Incidence: Counting new cases → measures how fast people are catching the disease over a
period in time.
Expressed as:
1) proportion of people who develop the disease (bv. 5%)
2) rate at which new cases of a disease have occurred (bv. 5000 new cases per 100.000 persons per
year)
Incidence proportion= aantal nieuwe zieke mensen in een bepaalde periode / aantal mensen die
risico lopen om het te krijgen
→ Proportion of population that develops a disease in a specific period
,Incidence rate= number of people who develop disease in a specific time period / total number of
person-time when people were at risk of getting the disease (alle Jaren die de mensen gevolgd zijn
bij elkaar optellen).
Hierbij moet je de personen die vanaf het begin af aan de ziekte al hadden eraf laten.
Als je weet wanneer de personen de ziekte hebben gekregen, moet je de tijd tot ze de ziekte kregen
vermenigvuldigen met het aantal personen die het hebben gekregen + de gehele tijd * het aantal
personen die tot het eind van het onderzoek zijn gevolgd.
250 per thousand persons per year.
Person-time = sum of persons * time
Because incidence rate includes persons entering and leaving study populations, whereas incidence
proportion assumes that those individuals were disease-free, it generally is more accurate than
incidence proportion for long-term studies.
Case fatality ratio: Proportion of people with a given disease who die from it in a given period.
- measure of the short term severity of an acute disease.
- No. of death from a disease in a specific period / no. of people diagnosed with the disease in same
period.
Closed population:
- Based on fixed membership
- No one can be added
- Becomes smaller with the time (people die/cure)
- everyone is followed
- You can calculate both IP and IR
Open population:
- Can take new members with time
- People move in & out
- Numbers remain about the same
- No follow-up when leaving
- You can only calculate IR
- If I want to say something about a specific disease in the Netherlands (=open population).
Relation between Incidence & Prevalence
P = IR x D
- Assuming that population doesn’t change
- Valid for diseases with low frequency
- Generally valid: P / (1-P) = IR x D
High prevalence + low incidence = long duration of the disease (mensen moeten lang genezen)
Use of incidence Use of prevalence
For acutely acquired diseases For more permanent states, conditions or
attributes of ill-health
More important when thinking of etiology of More important when thinking of societal
the disorder burden of the disorder including the costs and
resources consumed as a result of the disorder
, Andere termen waarbij het gebruikt wordt: Andere termen waarbij het gebruikt wordt:
- morbidity rate - disease rate at autopsy
- mortality rate - birth defect rate
- Case-fatality rate
- Attack rate. It's mainly used in the field of
infectious disease where many new cases
occur in a short time period (e.g. epidemic).
It’s an proportion.
Introduction to diabetes
Type 1 diabetes (5% heeft deze vorm): Auto-immune disease
- no production of insulin. Usually develops in childhood and patients require lifelong insulin
injections
Type 2 diabetes (90%): Metabolic disorder
Characterized by:
- hyperglycemia
- Altered lipid metabolism
Usually develops in adulthood (because of an unhealthy lifestyle)
Gestational diabetes: State of hyperglycemia
- developing during pregnancy
Complications can be:
- Macrovascular (grote vaten)
- stroke
- heart disease + hypertension
- peripheral vascular disease
- foot problems → diabetes is the most frequent cause of amputations
- Microvascular (kleine vaten)
- Diabetic eye diseases
→ May cause blindness
- Renal disease
→ may cause kidney failure
- Neuropathy → may cause foot problems
2 diagnostic criteria for pre-diabetes:
1) impaired (verminderd) fasting hyperglycemia (IFG)
- Fasting glucose level = 5.6 – 7.0 mM
2) Impaired glucose tolerance (IGT)
- fasting glucose < 7,0 mM + 2 hours post 75g glucose → 7.8 – 11.1 mM → IGT
Trends in diabetes & diagnosis
- sweet urine
- measure glucose levels
- oral glucose tolerance test
- Hba1c reflects glymeric control over past 6 weeks
Different screening methods causes different diabetes prevalence numbers
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