University of Ghana SPH Lecture on Prevention
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Transcript of University of Ghana SPH Lecture on Prevention
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PREVENTING THE CAUSES OF DISEASE
David Kim, PhD
Vestergaard Frandsen West Africa
18 March 2011
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BIRTH DEATH
HEALTH
DISEASE
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The Workplace
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Mine
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Busy Street
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Farm
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The Environment
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Indoor Cooking
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Swimming Pools
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Vehicular Emissions
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Prevention
The act of hinderingMerriam-Webter’s dictionary
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Prevention of Disease Requires…
1. Hazard identification
2. Dose-response assessment
3. Exposure assessment
4. Risk characterization
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Hazard Identification
Group Exercise:
You are part of a public health team that has been sent
to a neighbourhood of a city where parents have been
complaining of their children experiencing coughing,
runny noses, and fevers that won’t go away. The
number of children with these symptoms is growing
every year; the numbers are 4 times larger than
expected. With your team, discuss the possible causes
of these symptoms.
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Childhood Leukaemia in Woburn
• A 1981 Department of Public Health study confirmed a childhood leukaemia cluster in Woburn, MA. The number of cases was 4 times higher than the national average.
• Woburn has a 130-year industrial history that resulted in significant local deposition of chemical manufacturing waste.
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Epidemiology
• Epidemiology is the basic science of public health.
• Purpose is to study (1) the distribution of disease in a population, and (2) the determinants of that disease.
• Concerned with person, place, and time.
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Person
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Place
• Family
• Village
• City
• Country
• Continent
• Global
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Time
• Hour
• Day
• Week
• Month
• Year
• Decade
• Century
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Unit of Measure
1000 people living in Accracontracted the flu last year. Whatis the incidence rate?
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Relative Risk
The IR of swine flu when flying with Deltais 2 cases per 1000 people each week. TheIR of swine flu on all airlines is 1 case per1000 each week. What is the RR of gettingswine flu when flying with Delta?
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Woburn MA: person
• Child diagnosed with leukaemia before 19th
birthday.
• Diagnosed between 1969 and 1989.
• A resident of Woburn MA at the time of diagnosis.
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Woburn MA: place
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Woburn MA: time
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Woburn MA: Relative Risk
RR = 9
For those living near contaminatedwell water relative to all residentsof Woburn. Is there a reason forconcern?
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Summary of Epidemiology Studies
Advantages
• Study human populations.
• Can examine adverse effects associated with exposures to risk factors in real time.
• Convincing data if studies are conducted correctly.
Disadvantages
• Long time to execute
• Costly
• Difficult to establish causality
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Dose-Response Assessment
• Determine whether the causative agent can damage human cells/tissues/organs.
• Studies are typically conducted in laboratories.
• Fundamental science is toxicology
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Toxicology
Paracelsus, the father of
toxicology
“The dose makes the poison”
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Toxicokinetics
• What the body does to the chemical.
• Defined by absorption, distribution, metabolism, and excretion (ADME).
• Establishes the DOSE in dose-response.
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Toxicodynamics
• What the chemical does to the body.
• Defined by cellular damage, DNA modifications, protein concentration changes, etc.
• Establishes the RESPONSE in dose-response.
Decreased dopamine levels in Parkinson’s disease patients
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In Vivo Experiments
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In Vitro Experiments
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In Silico Experiments
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Dose-Response Curves
• NOAEL: No Observed Adverse Effect Level
• LOAEL: Lowest Observed Adverse Effect Level
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Dose-Response Curve for Cr(VI)
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Summary of Toxicology Studies
Advantages
• Highly controlled.
• Fast results.
• Can better establish causal relationship between dose and effect.
Disadvantages
• Laboratory conditions
• Extensive use of animals
• Questionable relevance to humans
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Exposure Assessment
Study of contaminant levels in:
– Air
– Water
– Soil
– Biological Samples
– Food
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Objectives of Exposure Assessment
• Measure the amount of contaminant in the environment.
• Record how often humans come into contact with the contaminant.
• Identify who comes into contact with the contaminant.
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Air Monitoring
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Water Monitoring
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Spoil Monitoring
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Biological Monitoring
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Summary of Exposure Studies
Advantages
• Quantitative
• Real-world values
Disadvantages
• High cost of conducting studies (i.e., analytical chemistry)
• Small number of samples due to intensive nature of studies
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Risk Characterization
• Final phase of a risk assessment.
• Integrates information collected from EPIDEMIOLOGY, TOXICOLOGY, and EXPOSURE ASSESSMENT studies.
• Qualitative and quantitative conclusions.
• Synthesizes all the information and recommends actions to prevent diseases from spreading.
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Risk Characterization for Cr(VI)
• Clearly there is an association between leukaemia and living where Cr(VI) levels are high.
• Toxicological studies demonstrate a positive dose-response, suggesting a causal relationship.
• Exposure studies have measured presence of Cr(VI) levels in drinking water that exceed health standards.
• All evidence seems to point to the need to reduce Cr(VI) levels in order to prevent childhood leukaemia from occurring.
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Final Group Exercise
• Small-scale mining in Ghana.• Mercury is used to clean gold
nuggets.• Mercury is associated with skin
cancer and other deadly ailments later in life.
• Environmental contamination has made water undrinkable.
• Biological monitoring shows that people are exposed to dangerous levels of mercury.
What evidence do you need to evaluate whether or not preventive action should be taken?