Population Health Epidemiology IV Flashcards
What did Clemmensen 1965 say about epidemiology?
- The aim of every epidemiology study in cancer is to prevent it
What is the definition of risk factor?
- An environmental, behavioural or biological factor confirmed by temporal sequence, usually increasing the probability of a disease occurring and if absent or removed, reduces the probability
- They are part of the casual chain, or expose the host to the casual chain.
- Once disease occurs, removal of risk factor may not result in cure
What is the concept of cause?
- Few diseases have single ‘cause’
- Most result from exposure of susceptible individuals to one of more causal agents
- Exposure to causal agent(s) does not inevitably result in disease
- Investigation of cause complex:
- characteristics of susceptible/resistant individual
- types of exposure to external agent
What is the selected Bradford Hill Criteria for Causal association ie Factor under study likely to cause disease?
- Strength of association
- Dose response
- Change in risk factor – reduction
- Time sequence
- Consistency
- Specificity – defined exposures
- Biological plausibility
- Experimental preventive trials
What is a cause?
- External agent which results in disease in susceptible individuals
What are confounding variables in regard to Causes?
- Concept of cause must be distinguished from concept of association
- Not all factors associated with occurrence of disease are causes
- Some factors may be associated independently with a causal agent but do not themselves cause disease or increase risk of developing disease
What is definition of Confounding variable?
- Particular type of extraneous variable which for some reason has been left uncontrolled.
- The result is that on looking at the findings of an experimental study, rather than only one possible variable exerting influence on outcome, there are found to be others, which are said to be confounding the results
What is an example of Confounding variable of Drug trial for control of hypertension?
Test group (drug); Placebo group (control)
Result: test group lower blood pressure than placebo group
Confounding: average age of test group significantly lower than control group. Hypertension age related, therefore result may be due to age difference rather than effect of drug.
What are some negatives of descriptive epidemiology?
- Can only go so far
- Patterns and trends not causes
- Hypothesis generating
- Ecological fallacy
What is a Risk factor hypothesis?
- Suggestion that exposure to a particular agent may cause the development of a particular disease if susceptible individual exposed to agent in question
OR - Suggestion that possession of certain characteristics (e.g. socio-economic status, ethnicity, genetics) may make disease outcome more likely if exposed to certain agents
Gained from descriptive epidemiology, clinical impression, lab studies
What are some examples of examination of descriptive data?
- Decrease in caries levels associated with War-time sweet rationing
- Higher incidence of oral cancer in West of Scotland compared with rest of UK
- Caries more prevalent in children from low socio-economic groups
In each case, ask question why which generates hypothesis
How can you investigate risk factor hypothesis?
- In animals can conduct experiments
- In humans can’t use experimental approach so;
- Start with generation of hypothesis
- Should be biologically plausible
- Use Analytic observational study
What are the three common indices of risk?
- Absolute
- Relative
- Attributable
What is absolute risk?
- Most basic measure
- Incidence rate of disease amongst people exposed to agent
- Not very useful, as assumes no risk incurred by people not exposed to agent
What is Attributable risk?
- Difference between incidence rates in exposed and non-exposed groups
- Represents the risk attributable to factor being investigated
What is Relative risk?
- Ratio of incidence rate in exposed group to incidence rate in non-exposed group
- Measurement of proportionate increase in disease rates of exposed group
- Makes allowance for frequency of disease amongst people not exposed to supposed harmful agent
What are Analytic Observational Studies?
- Search for association between factor or set of factors and a disease
- Observational - not experimental i.e. investigator does not design study to expose one group on purpose to suspected factor or factors
- Investigator observes what is happening normally in population
Involves comparing disease experience of two or more groups of people in relation to their possession of certain characteristics or exposure to a suspected factor of factors
What are the two main types of Analytic Observational Studies?
- Cohort
- Case-control
What are the aims of Analytic Observational studies?
- Designed to test specific hypotheses
- Aim to define risk factors of disease more precisely
- From results may be possible to suggest ways of preventing/controlling disease
What are the types of Study?
- Cross-sectional (Descriptive) which is observational
- Cohort (Analytical) which is Observational
- Case-control (Analytical) which is observational
- Experimental; Clinical trial/ interventional which is experimental
What are Cohort studies?
- Prospective studies
- Recruit group of people who have not manifest the disease at time of recruitment and assess risk factors
- Individuals observed over period of time to measure frequency of occurrence of disease among:
- people exposed to risk factor
- people not exposed to risk factor
What are Case-Control studies?
- Retrospective studies
- Compare individuals with disease (cases) with those without disease (controls)
- Trace back to assess risk factors:
Past histories and exposure to suspected harmful agents compared
What are the pros and cons to Case-Control studies?
- Less robust than cohort studies
- May be used for preliminary investigation of hypothesis, followed by cohort (if possible)
- Value of study profoundly affected by method of selection of cases and controls
- Controls should be random sample of population from which cases selected
What are the major Risk factors of Dental Caries?
- Frequent intake non-milk extrinsic sugars (NMES)
- Dental plaque bacteria
- Inadequate exposure to fluoride
- Inadequate supply of saliva
- Socioeconomic status
What is the Analytical epidemiology of Dental caries?
- Diet and dental caries
- Fluorides and dental caries
- Oral cleanliness and dental caries
- SES
What evidence is there for diet and dental caries?
- Human observational studies
- Human intervention studies
- Animal experiments
- Plaque pH studies
What is the Vipeholm study?
- Conducted in swedish mental hospital in 1940-50s
- Sugar in sticky retentive forms increased caries
- Consumption of sugar, even at high levels, at meal times is associated with only a small increase in caries increment
- Consumption of sugar both between and at mealtimes is associated with a marked increase in caries increment
What was the Turka Suagr Study 1972-1974 (Human intervention study)
Aim
- To test, using human subjects, whether sugars vary in their cariogenic potential
Hypothesis
- Xylitol containing foods would be less cariogenic than sucrose and fructose containing foods due to inability of plaque to produce acids from xylitol metabolism
Human test group diets
- Sucrose-containing foods
- Fructose-containing foods
- Xylitol-containing foods
Results
- Substitution of sucrose by xylitol resulted in substantial reduction in caries incidence
- Substitution of sucrose by fructose did not lead to significant reductions in caries increment
What animal studies have showed for diet and dental caries?
- Have shown that local fermentable CHO necessary for caries development
- Have investigated the relative cariogenicity of different sugars
- Have investigated the effect of sugar concentration on caries development
- Have shown the importance of frequency of sugar intake and caries development
What have plaque pH studies shown for diet and dental caries?
- Importance of frequency of sugar intake
- Investigation of different sugars and concentration of sugars
- Investigation of artificial sweeteners
- Investigation of the effect of snack foods on plaque pH
- Investigation of effect of meal patterns on plaque pH
- Used in Switzerland to test cariogencity of different sweets
What have animal studies shown for Plaque as a caries risk factor?
- Shown dental plaque pre-requisite for caries development
i.e. no caries development in rats bred with bacteria-free mouths
What have human studies shown for Plaque as a caries risk factor?
- Results mixed re importance of plaque amount
- Streptococcus mutans is the major, but not the only, species associated with caries
What have animal experiments shown for link between mutans streptococci and caries?
- Mutans streptococci (ms) cause caries in gnotobiotic animals in presence of sugar
- Virulence properties: acidogenic, aciduric, produce extracellular glucans and intracellular storage polysaccharides
What is the Analytical epidemiology of Periodontal disease?
- Clear evidence that plaque has a role
Gingivitis - Levels of oral hygiene and severity of gingivitis highly correlated
Periodontitis - Only small amounts of plaque are required to initiate in a susceptible patient
- Once initiated, progressive destruction is largely independent of patient’s oral hygiene
- Instead host response factors and the presence of specific pathogens within subgingival microflora => progressive periodontitis
What are the associations of severe periodontitis from population studies?
- Older age-groups
- men > women
- Ethnicity
- Diabetes
- Osteoporosis
- Low socioeconomic status
- Smoking
- Infrequent dental attendance
- Presence of certain bacterial pathogens [plaque]
What are the risk factors of perio?
- Factors predisposing to plaque accumulation (anatomical, iatrogenic)
Factors modifying the inflammatory response - Smoking
- Dose response relationship (2-5x increase over non-smokers)
- Diabetes
- type 1 and type 2 diabetes mellitus
- Linked to status of diabetic control
? two way process
Risk factors of Oral cancer?
- Smoking
- Passive smoke
- Alcohol in non-smokers
- Diet
- SES
- HPV
What is a cause?
- External agent which results in disease in susceptible individuals
