Lecture 3 & 4: Foundational Concepts in Health & Disease

Question 1

What happened with Typhoid Mary in 1906?

Answer 1

-Mary was a cook hired by a household
-The household got infected with typhoid fever
-The family investigates and finds that Mary worked in a place with typhoid fever a couple years ago but doesn’t have symptoms herself
-She tested positive for typhoid fever and become the first known symptomatic carrier
-Mary was forcibly confined to isolation

Question 2

What are some key points about Typhoid Mary story?

Answer 2

-Distinction between “healthy” and “diseased”
-First known asymptomatic carrier of typhoid
-Raised debate about perineal choices vs. public good (bc she went back and could have infected millions)

Question 3

What is the difference between infected and diseased?

Answer 3

Infected: Host is invaded by microorganisms, the organisms multiply, and the hosts immune system responds

Diseased: Infection causes clinical signs/symptoms

Question 4

TRUE OR FALSE: Not all infections cause disease.

Answer 4

TRUE
-Just like the ex with Typhoid fever, could be asymptomatic and not display symptoms

Question 5

What are asymptomatic carriers?

Answer 5

-Humans or animals infected with an infectious agent but remain clinically normal
-Epidemiologically significant –> bc they act as sources of infection, but are more difficult to detect than a clinically diseased individual
-Host does not appear sick, but they are still capable of spreading the pathogen

Question 6

What is the relationship between determinant and outcome?

Answer 6

Determinant “risk factor”
-Any factor that when altered produces a change in the frequency or characteristics of the outcome
-Also called” exposure, independent variable, predictor, explanatory variable

Outcome “disease”
-Also response or dependant variable (depends on the determinant)

Question 7

What is the epidemiological triad?

Answer 7

-Traditional model of infectious disease causation
-The interactions among these factors dictate the impact of any infection both individual and population levels

HOST-AGENT-ENVIRONMENT

Question 8

How does disease occurrence change the triad?

Answer 8

Health and disease is a balance/ spectrum of all 3
-Tipping point is when factors interact that cause disease to occur such as new environment, new variant etc
-Epi is determining what changed and how it can be prevented

Question 9

What factors that involve HOST-AGENT-ENVIRONMENT triad?

Answer 9

Host
-Age, gender, immune status, breed, species, physiological state

Agent
-Type (bacteria, virus etc), virulence, infectious dose

Environment
-Physical or social environment, air, water, soil, rainfall etc

Question 10

What are infectious agents?

Answer 10

Basically pathogens
-Bacteria
-Paracites
-Viruses
-Fungi
-Prions

Question 11

What are the routes of disease transmission?

Answer 11

1. Direct contact: direct body surface to body surface contact, causing physical transfer of microorganisms
2. Indirect contact: contact between person and contaminated object (door handles)
3. Droplets: droplets containing microorganisms generated during coughing, sneezing talking are propelled though air and land on another person
4. Airborne: microorganisms suspended through air
5. Common vehicle: contaminated items such as food, water, medications
6. Vector transmission: invertebrates carry infectious agents between vertebrates (ex mosquitos-borne, tick-borne)

**Vector: a living carrier that transports an infectious agent from an infected individual (or its waste) to a susceptible individual)

Question 12

Why is zoonoses a ‘notable mention’ in epi?

Answer 12

-Infectious agents that can be transmitted between non-human animals and humans vice versa (transmitted b/w animals and humans)
-Can be spread using any routes if transmission
-Big public health concern (> 75% of emerging diseases are zoonotic)

Question 13

What is the general progression of a disease?

Answer 13

-Exposure to sufficient cause
-Pathogenic process detectable
-Clinical disease evident
-Outcome (chronic/recovery)

Question 14

What is an Incubation period and a latent period? Where do they fall in the general progression of a disease?

Answer 14

Latent period: time b/w exposure and it being detectable

Incubation period (longer): time of exposure and having clinical signs of disease aka symptoms

Question 15

What are the levels of prevention?

Answer 15

Primary Prevention (anything to prevent being exposed)
-Alter susceptibility (vax)
-Reduce exposure (each hands)
-Health promotion

Secondary prevention (identify disease in earliest stage)
-Early detection
-Screening (cancer screening)
-Case-finding

Tertiary prevention (already have it but trying to reduce time to recover)
-Psychosocial, medical, vocational, physical rehabilitation

Question 16

Where do the levels of prevention fall in the general progression of a disease?

Answer 16

Primary- First before exposure
Secondary- Right as the pathogenic process is detectable
Tertiary- After clinical disease is evident (know you have it)

Question 17

What are temporal patterns of disease?

Answer 17

Sporadic
-no pattern (random) and usually infrequent (ie prevalence is usually 0)

Endemic
-Constant presence of disease with predictable pattern at an expected level (manageable and predictable) ex common cold

Epidemic
-Occurrence of disease at an increased level that is NOT predictable (ie it exceeds what is expected) ex racoon rabies In ON

Pandemic
-Epidemic crossing international boundaries (simultaneous global epidemics) ex H1N1, and COVID-19