PREVENTING THE CAUSES OF DISEASE

David Kim, PhD

Vestergaard Frandsen West Africa

18 March 2011

BIRTH DEATH

HEALTH

DISEASE

The Workplace

Mine

Busy Street

Farm

The Environment

Indoor Cooking

Swimming Pools

Vehicular Emissions

Prevention

The act of hinderingMerriam-Webter’s dictionary

Prevention of Disease Requires…

1. Hazard identification

2. Dose-response assessment

3. Exposure assessment

4. Risk characterization

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.

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.

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.

Person

Place

• Family

• Village

• City

• Country

• Continent

• Global

Time

• Hour

• Day

• Week

• Month

• Year

• Decade

• Century

Unit of Measure

1000 people living in Accracontracted the flu last year. Whatis the incidence rate?

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?

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.

Woburn MA: place

Woburn MA: time

Woburn MA: Relative Risk

RR = 9

For those living near contaminatedwell water relative to all residentsof Woburn. Is there a reason forconcern?

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

Dose-Response Assessment

• Determine whether the causative agent can damage human cells/tissues/organs.

• Studies are typically conducted in laboratories.

• Fundamental science is toxicology

Toxicology

Paracelsus, the father of

toxicology

“The dose makes the poison”

Toxicokinetics

• What the body does to the chemical.

• Defined by absorption, distribution, metabolism, and excretion (ADME).

• Establishes the DOSE in dose-response.

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

In Vivo Experiments

In Vitro Experiments

In Silico Experiments

Dose-Response Curves

• NOAEL: No Observed Adverse Effect Level

• LOAEL: Lowest Observed Adverse Effect Level

Dose-Response Curve for Cr(VI)

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

Exposure Assessment

Study of contaminant levels in:

– Air

– Water

– Soil

– Biological Samples

– Food

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.

Air Monitoring

Water Monitoring

Spoil Monitoring

Biological Monitoring

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

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.

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.

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?