NURS 340: UNIT 8 - EPIDEMIOLOGY & SURVEILLANCE
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A nurse studies how a disease is distributed in a community. What is epidemiology?
The study of distribution, determinants, and control of health problems in populations.
What is the key difference between clinical medicine and epidemiology?
Clinical medicine focuses on one patient; epidemiology focuses on populations.
Can a population-level finding predict exactly what will happen to one patient?
No. Epidemiology describes population patterns/probabilities, not guaranteed individual outcomes.
A nurse identifies the ages, locations, and dates associated with disease cases. What type of epidemiology is this?
Descriptive epidemiology.
Think: WHO + WHERE + WHEN
What are the three components of descriptive epidemiology?
Person, place, and time.
A nurse investigates why a disease is more common among factory workers. What type of epidemiology?
Analytic epidemiology.
Think: WHY + HOW
What does analytic epidemiology investigate?
Determinants/factors that explain why or how a health problem occurs.
What should a nurse generally do before investigating why a community health problem is occurring?
Establish a descriptive picture of who, where, and when.
A nurse evaluates whether a vaccination program reduced disease rates. What is the nurse doing?
Evaluating an intervention/program at the population level.
What are common nursing uses of epidemiology?
Identify causes/risk factors, monitor health, investigate interventions, and evaluate programs.
Who is associated with early descriptive epidemiology?
Hippocrates.
Who is the “father of epidemiology”?
John Snow.
What did Florence Nightingale demonstrate using epidemiologic techniques?
That improved nursing care decreased mortality.
A nurse is investigating an increase in influenza cases. Which information should the nurse collect first?
A. Possible causes of transmission
B. Effectiveness of treatment
C. Who is affected, where cases occur, and when they occur
D. Which intervention should be implemented
C. Who is affected, where cases occur, and when they occur
A nurse investigates whether contaminated water is responsible for increased gastrointestinal illness in a community. This is:
A. Descriptive epidemiology
B. Analytic epidemiology
C. Clinical medicine
D. Individual assessment
B. Analytic epidemiology
A study finds that a certain exposure increases disease rates. Which statement by the nurse is correct?
A. Every exposed person will develop the disease.
B. The finding predicts each individual's outcome.
C. The finding describes a population-level pattern.
D. Individual assessment is no longer necessary.
C. The finding describes a population-level pattern.
A nurse finds that most cases of a disease occur among people ages 65–75 who are retired. Which component is being described?
A. Place
B. Time
C. Determinants
D. Person
D. Person
A public health nurse wants to determine whether a new smoking-cessation program is effective. Which action best uses epidemiology?
A. Predict which individual clients will quit
B. Compare smoking rates before and after the program
C. Diagnose nicotine dependence
D. Determine which client will relapse
B. Compare smoking rates before and after the program
What are the three elements of the epidemiologic triangle?
Host, agent, and environment.
A nurse teaches a patient to receive an influenza vaccine. Which part of the epidemiologic triangle is being changed?
Host — vaccination decreases host susceptibility.
Which host factors can affect susceptibility to disease?
Age, immune status, genetics, previous disease, lifestyle, and occupation.
What are the four major types of agents?
Biologic, chemical, physical, and nutritional.
Examples:
Biologic → bacteria, viruses
Chemical → poison, smoke
Physical → trauma, radiation
Nutritional → nutrient deficiency or excess
A nurse identifies poor housing, crowding, and contaminated water as contributing to disease transmission. Which part of the triangle is involved?
Environment.
What is infectivity?
The agent's ability to enter a susceptible host and produce infection or disease.
What is pathogenicity?
The proportion of infected people who develop disease.
What is virulence?
The proportion of people with clinical disease who become severely ill or die.
⭐ Remember:
Infectivity = infection
Pathogenicity = disease
Virulence = severity/death
What are the six links in the chain of infection?
Infectious agent
Reservoir
Portal of exit
Mode of transmission
Portal of entry
Susceptible host
A nurse identifies the bacteria causing an infection. Which link is this?
Infectious agent.
Where does an infectious organism naturally live and multiply?
Reservoir.
Examples include people, animals, and the environment.
A patient with influenza coughs respiratory secretions into the air. Which chain-of-infection link is being identified?
Portal of exit.
How can an infectious agent travel from one host to another?
Through the mode of transmission.
Ex: direct contact, airborne, vehicle-borne, and vector-borne.
A nurse wears gloves when caring for a patient with an infectious disease. Which chain link is the nurse primarily protecting?
Portal of entry — gloves protect against organisms entering through broken skin or mucous membranes.
What is a susceptible host?
A person who lacks resistance and can become infected.
A nurse teaches a patient to cover their cough. Which link is the intervention targeting?
Portal of exit.
A nurse performs hand hygiene before and after patient care. Which link is being interrupted?
Mode of transmission.
A nurse uses insect control to reduce malaria transmission. Which link is being interrupted?
Mode of transmission through a vector.
A patient is placed in isolation to prevent an infectious disease from spreading. What is the purpose?
To interrupt transmission and prevent the agent from reaching susceptible hosts.
What is the most important principle when using the chain of infection?
Breaking ANY ONE link can prevent or reduce transmission.
Can a person carry and transmit an infectious agent without showing symptoms?
Yes. This person is a carrier.
Is the person who is clinically ill always the susceptible host?
No. A person can be a carrier without symptoms and still transmit the agent.
A nurse wants to prevent infection but cannot eliminate the infectious agent. What should the nurse remember?
The nurse can target the host, environment, or any link in the chain of infection.
A nurse administers a vaccine to reduce a patient's risk of influenza. Which component of the epidemiologic triangle is being modified?
A. Agent
B. Environment
C. Host
D. Reservoir
C. Host
A patient develops illness after exposure to radiation. Radiation is classified as what type of agent?
A. Biologic
B. Chemical
C. Physical
D. Nutritional
C. Physical
A nurse learns that 100 people became infected with a microorganism and 20 developed clinical disease. Which characteristic is being described?
A. Infectivity
B. Pathogenicity
C. Virulence
D. Susceptibility
B. Pathogenicity
A patient with influenza coughs into the air, releasing respiratory droplets. Which link is represented?
A. Reservoir
B. Portal of exit
C. Portal of entry
D. Susceptible host
B. Portal of exit
Which nursing action directly interrupts the mode of transmission?
A. Administering a vaccine
B. Covering a patient's cough
C. Performing hand hygiene
D. Treating the infection
C. Performing hand hygiene
A healthcare worker has no symptoms but carries and transmits an infectious organism to several patients. How should this person be classified?
A. Susceptible host
B. Reservoir only
C. Carrier
D. Portal of entry
C. Carrier
A nurse teaches adolescents to avoid drinking and driving. The adolescents are currently healthy. What prevention level is this?
Primary prevention — the goal is to prevent disease/injury before it occurs.
A client has no symptoms, but a screening test detects early cancer. Which disease stage was targeted?
Subclinical stage — disease is present, but symptoms have not appeared.
A client develops symptoms of pneumonia and seeks treatment. Which natural-history stage is occurring?
Clinical disease — symptoms have begun.
After a stroke, a client receives physical therapy to improve mobility. What prevention level is this?
Tertiary prevention — the disease has occurred and therapy reduces disability.
A city adds fluoride to its water supply without requiring residents to do anything. What type of prevention is this?
Passive primary prevention — disease is prevented without individual behavior change.
A nurse enrolls a healthy smoker in a smoking-cessation program. What type of prevention is this?
Active primary prevention — prevention occurs before disease and requires behavior change.
A client has abnormal cellular changes but feels completely healthy. Why would screening be appropriate?
The client is likely in the subclinical stage, when disease exists before symptoms develop.
A client had an MI and now attends cardiac rehabilitation to regain function. Why is this tertiary rather than secondary prevention?
The disease has already caused an impact; rehabilitation aims to reduce disability/limitations.
A healthy person receives an intervention that protects them regardless of whether they change their behavior. What prevention category should the nurse identify first?
Primary prevention; then determine whether it is passive based on the lack of behavior change.
A client is diagnosed only after symptoms appear. Which natural-history stage prompted the diagnosis?
Clinical disease — this is the stage when symptoms typically lead to diagnosis.
A person never develops symptoms but can transmit an infection to others. What should the nurse recognize?
The person is a carrier — asymptomatic but capable of spreading disease.
A community program aims to catch disease earlier so treatment can cure it before progression. Which prevention level should the nurse select?
Secondary prevention — it focuses on early detection and treatment.
A community nurse is planning interventions for adults who do not currently have cardiovascular disease. Which intervention represents primary prevention?
A. Cardiac rehabilitation after an MI
B. Screening adults for early coronary disease
C. Teaching adults to exercise regularly
D. Physical therapy after a stroke
C. Teaching adults to exercise regularly
A client has no symptoms but undergoes testing that identifies an existing disease. How should the nurse classify the intervention?
A. Primary
B. Secondary
C. Tertiary
D. Passive primary
B. Secondary
A nurse cares for a client who developed permanent weakness after a stroke. Which intervention best represents tertiary prevention?
A. Stroke-risk education
B. Blood pressure screening
C. Physical rehabilitation
D. Smoking prevention education
C. Physical rehabilitation
A state requires fluoride to be added to municipal drinking water. Residents do not need to change their behavior for the intervention to work. How should the nurse classify it?
A. Active primary
B. Passive primary
C. Secondary
D. Tertiary
B. Passive primary
A nurse asks a client to stop smoking to reduce the risk of developing lung disease. Which classification is most accurate?
A. Active primary
B. Passive primary
C. Secondary
D. Tertiary
A. Active primary
A client has developed pathologic changes from a disease but reports feeling completely normal. Which finding would the nurse expect?
A. The client is in the susceptibility stage
B. The client is in the subclinical stage
C. The client is in the recovery stage
D. The disease has necessarily resolved
B. The client is in the subclinical stage
A client with an established disease receives treatment intended to prevent the condition from worsening and increase the likelihood of cure. Which prevention level is being applied?
A. Primary
B. Secondary
C. Tertiary
D. Passive primary
B. Secondary
A nurse is evaluating a client who was exposed to a disease but has not developed it. Which stage is the client currently in?
A. Susceptibility
B. Subclinical
C. Clinical
D. Recovery
A. Susceptibility
A client develops symptoms after a period of undetected disease. Which change marks the transition into clinical disease?
A. Exposure occurs
B. Pathologic changes begin
C. Symptoms appear
D. Disability resolves
C. Symptoms appear
A nurse evaluates four interventions. Which one specifically targets the lasting effects of an already-established disease?
A. Adding iron to cereal
B. Cancer screening
C. Teaching safe driving
D. Occupational therapy after brain injury
D. Occupational therapy after brain injury
A client has no symptoms but continues to transmit an infectious disease to family members. Which explanation is most appropriate?
A. The client is susceptible but infected
B. The client is a carrier
C. The client is experiencing recovery
D. The client has only been exposed
Answer: B — The client is a carrier.
A carrier can spread disease despite having no symptoms.
B. The client is a carrier
A nursing student says, “Anything that happens before symptoms is primary prevention.” Which scenario best demonstrates why this statement is incorrect?
A. A healthy person receives fluoride
B. A healthy person stops smoking
C. An asymptomatic person receives cancer screening
D. A healthy person receives injury-prevention education
C. An asymptomatic person receives cancer screening
A health department counts only new cases of influenza occurring this month. Which measure should the nurse use?
Incidence — measures new cases occurring in a population at risk.
A nurse wants to know how many people in a community currently have diabetes, including people diagnosed years ago. Which measure is appropriate?
Prevalence — includes all existing cases (new + old).
An outbreak causes a sudden increase in new cases of food poisoning. Which epidemiologic measure would rise first?
Incidence — it directly reflects the number of new cases.
A chronic disease has many existing cases that remain in the population for years. What happens to prevalence?
Prevalence increases because cases accumulate over time.
A disease has many new cases each year but usually resolves within several days. Why might prevalence remain low?
Short disease duration limits prevalence, even when incidence is high.
A nurse is estimating how many treatment resources are needed right now for people living with a chronic disease. Which measure is most useful?
Prevalence — estimates the current population burden.
A nurse compares the number of new tuberculosis cases this year with the population at risk. What is being calculated?
Incidence = new cases ÷ population at risk.
A nurse reports the proportion of residents who have asthma on June 1. What type of prevalence is this?
Point prevalence — measured at one specific point in time.
A nurse reports the proportion of residents who had asthma at any time during 2026. What type of prevalence is this?
Period prevalence — measured across a specified time span.
Two diseases have the same incidence, but Disease A lasts much longer. Which disease will generally have higher prevalence?
Disease A — longer duration increases prevalence.
A nurse notices that prevalence is increasing even though the incidence has remained stable. What could explain this?
People are living with the disease longer, increasing the number of existing cases.
A nurse is investigating how rapidly a new infectious disease is spreading. Which measure should receive priority?
Incidence — it tracks how quickly new cases are emerging.
A community nurse reports 50 new cases of a disease among 10,000 people who could develop it during one year. Which measure is being calculated?
A. Prevalence
B. Incidence
C. Point prevalence
D. Period prevalence
B. Incidence
A nurse needs to determine how many community residents are currently living with diabetes, regardless of when they were diagnosed. Which measure should be used?
A. Incidence
B. Point prevalence
C. Mortality
D. Attack rate
B. Point prevalence
A disease causes 500 new cases in a population each year, but most affected individuals recover within one week. Which pattern is most likely?
A. High incidence and high prevalence
B. Low incidence and high prevalence
C. High incidence and relatively low prevalence
D. Low incidence and low prevalence
C. High incidence and relatively low prevalence
A chronic disease has a stable incidence, but advances in treatment allow affected individuals to live much longer. What is the expected effect?
A. Prevalence decreases
B. Prevalence increases
C. Incidence must increase
D. Incidence becomes zero
B. Prevalence increases
A public health nurse wants to detect whether an infectious disease outbreak is producing more new cases than usual. Which measure is most useful?
A. Incidence
B. Prevalence
C. Point prevalence
D. Period prevalence
A. Incidence
A nurse reports that 8% of a city's population had influenza at some point between January and March. Which type of measure is being described?
A. Point prevalence
B. Period prevalence
C. Incidence
D. Case-fatality rate
B. Period prevalence
Two diseases have identical incidence rates. Disease X usually resolves within days, while Disease Y lasts for decades. Which statement is most accurate?
A. Disease X must have greater prevalence
B. Disease Y will generally have greater prevalence
C. Both must have identical prevalence
D. Duration does not affect prevalence
B. Disease Y will generally have greater prevalence
A nurse reviews epidemiologic data and finds that diabetes prevalence is increasing. Which explanation is most consistent with this finding?
A. Existing cases are accumulating because people live with diabetes for long periods
B. Every person with diabetes is recovering rapidly
C. Only new cases are included in prevalence
D. Prevalence measures only people who developed diabetes this year
A. Existing cases are accumulating because people live with diabetes for long periods
A nurse counts everyone who has asthma on October 3, regardless of when they were diagnosed. What is being measured?
A. Incidence
B. Point prevalence
C. Period prevalence
D. Population at risk
B. Point prevalence
A hospital administrator wants to estimate the current burden of heart failure to determine staffing and treatment resources. Which measure is most useful?
A. Incidence
B. Prevalence
C. New-case rate only
D. Population at risk
B. Prevalence
A lifelong viral infection continues producing new cases, while infected individuals remain infected for life. What pattern should the nurse expect over time?
A. Incidence and prevalence both tend to rise
B. Incidence falls while prevalence becomes zero
C. Prevalence stays low because duration is short
D. Incidence measures all existing cases
A. Incidence and prevalence both tend to rise
A nurse sees that Disease A has a higher incidence than Disease B but a lower prevalence. Which explanation best accounts for this finding?
A. Disease A has a much shorter duration
B. Disease A has no new cases
C. Disease B cannot be chronic
D. Prevalence counts only new cases
A. Disease A has a much shorter duration
A nurse investigates a food-poisoning outbreak and finds that 30 of 100 people who ate the contaminated meal became ill. Which measure should the nurse calculate?
Attack rate — used for infectious outbreaks: sick ÷ exposed.
A patient asks, “Of the people who already have this disease, how many die from it?” Which measure answers this question?
Case fatality rate (CFR) — deaths from the disease ÷ people diagnosed with the disease.
A disease has a 25% CFR. What is the corresponding survival rate?
75% — survival = 1 − CFR.
A health department wants to know the overall death rate in a city, regardless of cause. Which measure should it use?
Crude mortality rate — deaths from all causes ÷ population.
A nurse wants to determine how many deaths in a population were caused specifically by lung cancer. Which measure is appropriate?
Cause-specific mortality rate — deaths from one specific cause ÷ total population.