Public Health & Study Disease &Epidemics Exam 1

A disease with a high level of morbidity but a low level of mortality would show which of the following characteristics:

Lots of symptoms, not that many deaths

Which of the following are examples of acute diseases? (Select all that apply)

Common Cold

Flu

Preventing individuals with one or more risk factors for a disease from developing that disease is an example of which level of prevention?

Primary Prevention

The Chicago Department of Public Health reported 3 new cases of West Nile Virus in August. This is an example of

Incidence

Health

state of complete physical, mental and social well-being
and not merely the absence of disease or infirmity.

What is Disease?

A disorder of structure or function
-especially one that produces specific signs or symptoms or that
affects a specific location and is not simply a direct result of physical
injury.

Public Health Definition (WHO)

-refers to all organized measures (whether public or
private) to prevent disease, promote health, and prolong life among
the population as a whole.

-Its activities aim to provide conditions in which people can be healthy
and focus on entire populations, not on individual patients or
diseases

Anatomic

by organ or tissue (lung disease)

Physiological

by function or effect (respiratory disease)

Pathological

by the nature of the disease process (infectious,
inflammatory, neoplastic etc)

Etiologic

cause (staphylococcal diseases—pneumonia, meningitis,
skin infections)

Mode of transmission

Vector-borne, water borne, food borne, air
borne

Acute disease

develop
suddenly and have a relatively
short duration, usually lasting for
a few days to a few weeks.

Chronic disease

are long-term
health conditions that persist
over an extended period, lasting
for months to years, and often
require ongoing management
and treatment

Communicable diseases

Can spread from person-to-person
• Generally infectious diseases (flu, COVID, HPV, measles, cold, etc)

Non-communicable diseases

Cannot spread person-to-person
• E.g. cardiovascular diseases, cancers, and diabetes.

Communicable Disease:
Latency Period

Time interval
between when an individual
is infected by a pathogen and when
that individual becomes infectious,
i.e. capable of transmitting pathogens
to other susceptible individuals.

Communicable Disease:
Incubation period

Time interval from
exposure to a pathogen to showing
symptoms

Noncommunicable Disease:

Latency Period: Time that passes
between being exposed to something
that can cause disease (such as
radiation or a chemical) and having
symptoms

Morbidity

the state of being symptomatic or unhealthy for a disease
or condition. It is usually represented or estimated using prevalence
or incidence

Mortality

the number of deaths caused by the health event under
investigation. It can be communicated as a rate or as an absolute
number

Incidence

the occurrence of new cases of disease or injury in a
population over a specified period of time

Prevalence

the proportion of persons in a population who have a
particular disease or attribute at a specified point in time or over a
specified period of time.

Prevalence formula

incidence x average duration

Epidemiology

The study of the distribution and determinants of health-related
states or events in specified populations and the application of this
study to control health problems.

Exposure

any factor that may be associated with the outcome of
interest.
• Also called the independent variable or risk factor
• Can be a microorganism, a chemical, a behavior, an environmental exposure,
even a treatment or preventive measure

Outcome

the variable that is studied to assess the impact of the
exposure on the population.
• Aka the dependent variable
• Usually a health outcome: presence/absence of a disease or injury

Exposures & Outcomes

For example, in a study looking at nerve damage after
organophosphate poisoning, the exposure would be
organophosphate and the outcome would be nerve damage.

Risk Factors

any attribute, characteristic or exposure of an
individual that increases the likelihood of developing a disease or
injury

The factor which is the difference between an outbreak and a cluster

The number being above what is normally expected in that population in that area

You should wait to implement control measures until you have completed all prior steps of the outbreak investigation in order.

False

Why should you continue to monitor cases after implementing control and prevention measures? (select all that apply)

-To make sure the incidence of disease is slowing down or stopping

-Because continued new cases could point you to the need for further controls or areas/populations that were missed with your existing controls

Cluster

an aggregation of cases grouped in place and time that are
suspected to be greater than the number expected, even though the

Outbreak

refers to an increase, often sudden, in the number of cases
of a disease above what is normally expected in that population in
that area

Epidemic

has same definition as outbreak but is often used for a
more widespread geographic area. (“Outbreak” is also sometimes
used instead of “epidemic” to quell public anxiety)

Pandemic

similar to epidemic, but has spread over several countries
or continents, usually affecting a large number of people

Incubation Period

The time between exposure to a pathogenic organism, chemical, or
radiation, and when symptoms and signs first appear

Latent Period

-The period between exposure and the onset of the period of
communicability
-This may be shorter or longer than incubation period.

Common/Point source

the exposure
period is short and all cases will have a
similar incubation period
• Ex. Contaminated potato salad at a picnic

Intermittent Common Source

patients
are exposed to the source of the
disease at irregular intervals. An
intermittent common-source outbreak
means patients are exposed to the
source of the disease at irregular
intervals.
• Ex: Swimming in Lake Michigan near the
Chicago locks after heavy rains vs. normal
conditions

Propagated or progressive epidemics

occur when the infection spreads from
person to person, either directly from
person to person (e.g. via hand shaking
or kissing), or indirectly via vectors (e.g.
mosquitoes in the case of malaria), or
in water, food or another medium

Mixed epidemics

show characteristics
of both common source and
propagated epidemics. A mixed
epidemic often starts with a common
source and is followed by a propagated
spread. Mixed epidemics are often
caused by foodborne infectious agents
like S. typhi-typhoid fever

Outbreak Investigation

A set of procedures used to identify the cause of a disease outbreak.
• It is also used to identify:
• The people affected
• The circumstances and mode of spread of the disease
• Other relevant factors involved in propagating the epidemic.

case definition

a standard set of criteria for
deciding whether an individual should be classified as having the
health condition of interest

Descriptive Epidemiology

describes the
where and whom of the disease, allowing
you to begin intervention and prevention
measures.

Differential Diagnosis

a systematic process used to identify the
proper diagnosis from a set of possible competing diagnoses

Epidemic OR Outbreak

is an increase, often sudden, in the number
of cases of a disease above what is normally expected in that
population in that area.

What is surveillance?

The ongoing systematic collection, analysis, and interpretation of
health-related data

Active Surveillance

system employing staff members to regularly contact heath care
providers or the population to seek information about health conditions.
• provides the most accurate and timely information, but
it is also expensive

Rate

An expression of the frequency with which an event occurs in a
defined population.

number of events in a specified period/
average population during the period

Why standardize the rate per population?

Population change over time—we are being a bit simplistic only
comparing one year to the last
• Would likely look at trends aggregated over time (why?)
• Seasonal population changes—college, agricultural, resort towns, etc

Which of the following is a key difference between viruses and bacteria?

Bacteria can grow and reproduce outside of host cells, while viruses cannot

Which of the following differentiates active TB disease from latent TB infection?

Both have positive TB blood or skin tests, but only active TB will have symptoms

A person with latent TB infection cannot spread TB

True

Which of the following are risk factors for getting TB? (select all)

1. Work in places where TB is more likely to spread, such as hospitals, homeless shelters, correctional facilities, and nursing homes

2. Use of immune-suppressing medication such as chemotherapy

3. Being a child under 5 who is exposed to TB

How Do You Define A Case?

-Demographic Factors
-Clinical Factors

What is Tuberculosis?

-Tuberculosis (TB) is caused by a bacterium
called Mycobacterium tuberculosis.

• M. tuberculosis divides every 18–24 hours
(This is extremely slow compared with
other bacteria! For example, E. coli can
divide ~ every 20 minutes

Incubation period is 3-8 weeks

Spread

Tuberculosis spreads through the air when people
with active pulmonary TB cough, sneeze, speak, or
sing, releasing tiny airborne droplets containing the
bacteria.

Lines of Defense--Physical

• Mucus
• Cilia

Development of Disease

• The blood carries monocytes to the
lung, where they enter the lung and
become macrophages.
• The macrophages surround and try to
eat M. tuberculosis but they are unable
to kill and digest the bacterium because
of its waxy exterior wall.

The bacteria then survives and makes copies of
itself within the macrophage, eventually
destroying the macrophage and releasing more
bacteria into the lung.
• In the next stage of infection, healthy
macrophages (and a few other white blood cell
friends) try to surround and isolate the
infected macrophages-->the formation is called
a granuloma
• Granulomas are not specific to TB, but can
occur in any disease or inflammatory situation
where the immune system attempts to isolate
foreign substances that it is otherwise unable
to eliminate

This does not destroy the tuberculosis
bacteria, but contains them, preventing
spread of the infection to other parts of
the body.
• In tuberculosis, the granuloma contains
dead tissue at its center, and appears as a
small white nodule on X-rays, also known
as a tubercle

Tubercle

-This does not destroy the tuberculosis
bacteria, but contains them, preventing
spread of the infection to other parts of
the body.
- In tuberculosis, the granuloma contains
dead tissue at its center, and appears as a
small white nodule on X-rays

Latent TB infection

As long as the infection is contained
within granulomas, there are no
outward symptoms and the person is
said to have

Active TB disease

If the immune system is unable to
control the infection, the bacteria can
spread through the lung and even
enter into the blood stream from an
area of damaged tissue spreading to
areas such as such as the kidney,
spine, and brain and causing
symptoms

Latent→Active TB

Without treatment, people with latent TB can develop active TB
disease at any time and become sick

A complete medical evaluation for TB disease has five components:

•Medical history
• Physical examination
• TB Blood or skin test
• Chest X-ray
• Examination of sputum (microscopy, culture, other tests

Interferon-gamma release assays test

for the presence of TB antigens in
a patient’s blood

Antigen

any substance that is capable of stimulating an immune
response

Case Definition

• is a standard set of criteria for deciding whether an
individual should be classified as having the health condition of
interest.
• Used to characterize outbreak and to discover other cases related to
outbreak

Inclusion criteria:

characteristics that the prospective cases must have
if they are to be included in the potential outbreak.

Exclusion criteria

are those characteristics that disqualify prospective
cases from being included in your outbreak population