Epidemiology in Public Health

Lesson Tasks

• Epidemiology: The Backbone of Public Health is useful for understanding the lesson with a 6 minute video
• It is important to read the CDC’s epidemiology module, complete exercises, and knowledge check assignments up to topic #3
• Essential to read the article regarding Grassy Narrows mercury victims
• Reviewing online lesson notes and completing non-graded activities is key for graded assessments
• Complete three discussion posts during this academic term

Lesson Outcomes

• Understanding epidemiology and is crucial to public health is key
• Recognize the differences between descriptive and analytic epidemiology
• Describe how epidemiology is applied in public health
• Describe the epidemiological triangle and its uses to understand epidemiological problems
• Explain host, agent, environment, and time characteristics in relation to epidemiology
• Survey the utilization of surveillance for epidemiological data collection

Key Terms

• Epidemiology is a key term for this lesson
• Descriptive Epidemiology is a key definition
• Analytic Epidemiology falls under key definitions
• Evidence is a key term
• Epidemiologic triangle is a key term to understand
• Agent/host/environment are features that need to be defined

Lesson 6 Introduction

• Epidemiology is a branch of public health focused on measuring and analyzing health and illness patterns in populations
• Unlike public health policy, it is quantitative, thus uses math to understand illness at a population level through numbers
• It complements and expands material from assigned readings and videos
• The material is closely aligned with CDC modules, offering multiple explanations for better understanding

What is Epidemiology?

• The WHO defines epidemiology as "...the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems.”
• The CDC says it relies on a systematic, unbiased approach to collecting, analyzing, and interpreting data
• Epidemiologic methods use observation and valid comparison groups to assess differences, such as disease cases or exposure frequencies
• Epidemiology studies patterned health and disease across populations over time, using surveillance data to examine disease distributions
• Epidemiology models future health issues and plans interventions

Analytic vs. Descriptive Epidemiology

• Epidemiology relies on quantitative study designs
• Descriptive epidemiology answers who, what, and where questions, characterizing disease amount and distribution
• Descriptive epidemiology is a critical first step for any epidemiological investigation
• Early COVID-19 epidemiology used surveillance and contact tracing to locate the virus, determine disease prevalence, and identify affected populations
• Analytic epidemiology asks "why" and "how" questions to understand causality patterns around certain diseases
• COVID-19 analytic epidemiology identified risk factors and how it spread
• Experimental epidemiology is an analytic form that tests interventions through controlled comparison, such as mask mandates and vaccines

Epidemiology in Practice: Applications

• Historical epidemiology studies trends in disease historically to understand health and illness changes
• Historical epidemiology uses sources like newspapers, reports, census data, personal accounts etc
• Historical epidemiology is useful for current disease analyses, for ideas on how to cope with a present disease
• Community epidemiology aids community planning and advocacy, often using descriptive methods to depict overall community health
• Community epidemiologists work with local health units, Community Health Centres, universities, or NGOs
• Epidemiology for policy, organization, and governance can be descriptive or analytic, to understand the population or intervention for policy development
• Policy development uses existing epidemiological data or new, targeted studies
• Policy studies are conducted by civil servants in policy-generating government arms, such as Public Health Ontario or the Public Health Agency of Canada
• Clinical epidemiology tracks new conditions/clinical interventions and supports existing interventions
• Clinical epidemiology takes place within university kinesiology departments, also within research and development departments of pharma companies, or within hospital settings

A Special Note About Correlation

• Correlation does not imply causation, which is an important golden rule about epi
• Epidemiological studies reveal correlations
• Early COVID-19 epidemiology showed people with certain blood types were more susceptible to severe COVID-19
• It's important not to misread correlation as causation, as other variables come into play
• Epidemiological studies are not designed to investigate individual, granular-level effects of disease
• Other study designs are needed to determine causality

The Epidemiological Triangle

• The epidemiological triangle is a tool epidemiologists use - it breaks down a disease or health issue into inter-related parts
• One point represents the agent which is what is triggering the disease or health issue
• One point represents the host which is the entity experiencing the disease or health issue
• One point represents the environment, which is the space or place in which the disease or health issue occurs
• Some triangles feature “time” in the middle of the triangle, representing a timeframe in which the disease or health issue occurs
• The cholera triangle includes:
  • The agent is vibrio cholera: a waterborne bacterium whose toxic by-products cause intense, often fatal gastroenterological distress in humans
  • The hosts are human beings who live in dense, crowded areas without adequate access to clean water sources. This often means the hosts live in some degree of poverty, and thus may not have the means to adequate assistance
  • The environment is contaminated water, in which cholera lives and which is used by humans for drinking or cleaning purposes

Sources of Epidemiological Data

• There are ways of collecting epidemiological data from various sources
• Methods have been discussed from a few lessons ago when surveillance was talked about
• Data can be divided into: primary and secondary

Primary Data

• Primary data are collected to answer questions about the epidemiological issue under investigation
• Surveys, questionnaires, interviews with key informants, physical examinations, and ethnographic observations gather primary data
• Primary data are collected to answer the epidemiological study

Secondary Data

• Secondary data has already been collected for other purposes
• Often, sources of this data are collected as part of larger efforts to maintain population-level data, like censuses
• Census data, birth and death records, hospital and physician records, household surveys, insurance and actuarial data, local population data, and media sources are sources of secondary data
• These datasets are originally collected for other reasons than the epidemiological issue being asked in question

Global Public Health Information Network (GPHIN)

• Canada hosts a public health program called the Global Public Health Information Network (GPHIN)
• GPHIN collects and analyzes media outputs globally to warn about biological, nuclear, chemical, and radiological threats
• GPHIN collects, culls, and crunches multilingual data including media forms across the world

Reflection Activity: The Grassy Narrows Story

• Epidemiology can help "see" health concerns in marginalized populations, providing "hard" evidence

• Epidemiology fosters equity and action for issues rooted in inequality

• Grassy Narrows is a reserve in northern Ontario on a waterway polluted by industry. 90% of residents suffer from mercury poisoning

• The advocacy from Grassy Narrows members, who were bolstered by work from epidemiologists since the 1970s, the mercury poisoning issue has gotten political traction over the past decade

  1. Using the article and movie on Grassy Narrows, please fill in the below epidemiologic triangle (in your notes) with as much detail as you can about the Grassy Narrows mercury crisis in terms of agent, host and environment (person, pollutant and place).

• The agent of Grassy Narrows mercury crisis is mercury, which is a toxic heavy metal for industrial processing. It ingested when humans are in contact with it

• Mercury poisoning happens from ingesting mercury contaminated environments; in particular, ingesting contaminated food and water

• The mercury crisis host are the people of Grassy Narrows, who are from the Asubpeeschoseewagong First Nation. People live in a remote reserve with scant attention, is largely impoverished, and lacks critical infrastructure

• The environment is the Grassy Narrows river and soil. The Dryden Chemical Company dumped mercury into the river, which contaminated the area

• Mercury bioaccumulates from tiny organisms up the food chain where humans ingest

• The time frame for this unfolded is of over many generations from 1962-1970

  2. What sources of data did the researchers use in order to reach their conclusions?

• Researchers used both primary and secondary data for this study

• Local questionnaires, surveys and physical testing (hair sampling) are primary data, while comparing these results to household health surveys taken from other First Nations communities across Canada is secondary data

  3. The authors of this study have chosen to compare residents of Grassy Narrows to other First Nations people in Canada. Why do you think they chose a smaller comparison group? What do you think the results would have looked like if the study authors had only compared the residents of Grassy Narrows to the general Canadian population?

• The authors used a smaller comparison group to account for the variables like racism

• Other First Nations groups act as a more consistent control group with similar host attributes, which better helps to allow researchers to better understand the impact of agent and environment interaction

• Without this attribute consideration, then results of the surveys may have looked more difficult than results from other surveys done with Canada’s general population

  4. Is this a descriptive or analytic study?
  • It’s an analytic study because it asks “why” and “how”, and uses comparison as a methodology
  5. How might this study be used to influence policy and planning? What kind of road map for change or intervention does this evidence provide?
  • The study would lead to multiple interventions, like remediation of the river, water treatment, financial compensation, and access to remediative health care
  • Study can foster preventative health policy, this would call for stronger regulations and stronger sanctions on companies that pollute

Conclusion

• The lesson covered the basics of epidemiology including a general overview, differentiating between descriptive and analytic epidemiology, the epidemiological triangle, thinking about epidemiological data sources, and applying concepts to a real-world problem.
• The upcoming module will step into the math branch and engage some of the most-used concepts in epidemiology: incidence, prevalence and mortality
• It’s important to also note what First Nation’s Chief Rudy Turtle said: "With this health survey and with the discovery of mercury, it's just a very dark picture….But at the same time, our people are doing the best they can to live under the conditions they're living in….But we do need help."