1. Assume we have a group of workers in a factory and many of them already have a respiratory
illness. We want to design a study to evaluate if exposure to some specific factor relates to the
illnesses. What study design should we use and how would we conduct the study?
2. Imagine that an industrial hygienist and a safety engineer identify that there is an exposure to
a new chemical that represents a major health hazard in your factory. They immediately
recommend that all of the employees exposed to the chemical use a specific and appropriate type
of PPE. Is this the only thing they should do? What other control measure should we consider
and potentially implement as management of the factory? Why?
3. What is indicated by a LD-50? What is indicated by ED-50? What might it mean if the ED50 equals the LD-50?
Module 5: Recognition, Assessment, and
Prevention
Dr. Neyens
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Chapter 24: Epidemiology
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Epidemiology
• Epidemiology is the study of the distribution and determinants
of disease frequency among populations.
• The goal of this field is to identify and investigate hypotheses
about the causal relationships between exposures and diseases
or injuries
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How do we quantify exposure?
• Accurate exposure measurement is critical?
• Issues with exposure measurement:
– Exposures are not usually constant in space and time
– Workers are hired and fired/quit
– Exposures vary over time due to process changes
– Exposures can change based on weather, temperature, etc.
– Personal exposures are difficult to collected
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Example of quantifying exposure
• Car crashes
– We can count the number of crashes that occur in an area for a group of
people.
– Let’s say that there are 5,000 crashes in SC involving 16-year-old drivers
during 2013.
– That could be a lot or it could be very few
– We need to account for exposure of some sort
• We could count
– The number of 16-year-olds
– The number of 16-year-olds who drive
– The number of miles that 16-year-olds drive
– The amount of time that 16-year-old drivers drive
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Measures of disease occurrence
• Incident proportions
• Prevalence (prevalence rates)
• Rate ratios and risk ratios
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How do we interpret and understand rates?
• Crude ratesà Calculated without accounting for exposure (e.g.,
16-year-old drivers crashes per population)
• Specific ratesà Calculated for homogeneous groups (e.g., 16year-old drivers’ crashes per 16-year-old drivers)
• Adjusted ratesà Rates adjusted for other types of exposures or
groups (e.g., 16-year-old drivers’ crashes per mile driven by
16-year-olds)
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Study designs
• Cross sectional studies à whole population, snapshot in time,
examines the association between exposure and health outcome
• Cohort studiesà large populations, longer study, identifies
those exposed and those not exposed, and follows them to see if
health outcomes occur
• Case-control studiesà smaller populations (typically),
identifies those with a health outcome and those without and
identifies differences in exposure.
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Precision and validity
• These study designs are not random controlled trials (or clinical
trials) so we need to think about biases and validity
– Selection bias: Who is selected from a population for a study (ideally
random, but not always possible).
– Information bias: Like measurement errors, wrong information can
lead to incorrect conclusions
– Confounding bias: Something outside of the study is affecting the
relationship between exposure and health outcomes
– Healthy worker bias: Healthy workers will more likely be employed
and willing to participate, sick workers may not still be employees.
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Chapter 25: Toxicology
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Toxicology
• The study of the harmful effects of chemicals on living
organisms.
• For a chemical to actually have an effect, it must follow an
exposure pathway to get to the organism’s system or organ or
cells that the chemical might affect.
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Dose-response relationship
• D-R curves describe how a particular response increases as the dose
of a chemical (or something) increases.
• Effect dose-50 (ED50):
The dose that produces a
specific effect in 50% of
the population
• Lethal dose-50 (LD-50):
A dose that kills 50% of
the population
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Chapter 26: Occupational and Environmental
Hygiene
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Occupational (Industrial) Hygiene
• Environmental science concerned with anticipating,
recognizing, evaluating and controlling health hazards in the
workplace
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Controlling hazards
• Strategies for controlling hazardous exposures
Once identified PPE should be used immediately until the
following controls can be used.
– 1. Change industrial process or materials to reduce exposure
– 2. Isolate the hazard and install engineering controls
– 3. Use administrative controls, controlled schedules, limited
exposures, and lastly prolonged use of PPE (e.g., PPE only).
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