Public health 1st exam

A community has 2,000 residents. On January 1, 200 residents already have a chronic disease. During the year, 100 new cases are diagnosed. No residents with the disease recover or die during the year.

What are the incidence and end-of-year prevalence?

A. Incidence = 5%; Prevalence = 10%
B. Incidence = 5.6%; Prevalence = 15%
C. Incidence = 10%; Prevalence = 15%
D. Incidence = 15%; Prevalence = 5.6%

Answer: B

Rationale: Incidence measures new cases among the population at risk. The 200 people who already had the disease are removed from the at-risk denominator.

Population at risk = 2,000 − 200 = 1,800

Incidence = 100 ÷ 1,800 × 100 = 5.6%

Prevalence includes all existing cases. At the end of the year, there are 200 previous cases + 100 new cases = 300 cases.

Prevalence = 300 ÷ 2,000 × 100 = 15%

Remember: Incidence = NEW. Prevalence = ALL existing.

A PHN studies whether exposure to a workplace chemical increases respiratory disease.

Among 300 exposed workers, 90 develop respiratory disease.
Among 500 unexposed workers, 50 develop respiratory disease.

Which interpretation is correct?

A. RR = 2.0 and attributable risk = 10%
B. RR = 3.0 and attributable risk = 20%
C. RR = 0.33 and attributable risk = 20%
D. RR = 3.0 and attributable risk = 30%

Answer: B

Rationale:

Risk in exposed workers:

90 ÷ 300 = 30%

Risk in unexposed workers:

50 ÷ 500 = 10%

Relative Risk:

30% ÷ 10% = 3.0

The exposed workers have 3 times the risk of developing respiratory disease compared with the unexposed workers.

Attributable Risk:

30% − 10% = 20%

So, 20 percentage points of risk are associated with the exposure. Your slides define relative risk as incidence in the exposed group divided by incidence in the nonexposed group, while attributable risk is the difference between the two incidence rates.

A new screening test is evaluated in 1,000 people.

Of 120 people who actually have the disease, 96 test positive and 24 test negative.

Of 880 people without the disease, 792 test negative and 88 test positive.

What are the test's sensitivity and specificity?

A. Sensitivity = 80%; Specificity = 90%
B. Sensitivity = 90%; Specificity = 80%
C. Sensitivity = 96%; Specificity = 88%
D. Sensitivity = 20%; Specificity = 10%

Answer: A

Rationale:

Sensitivity asks:

Of everyone who HAS the disease, how many did the test correctly identify?

Sensitivity = TP ÷ (TP + FN)

= 96 ÷ (96 + 24)

= 96 ÷ 120

= 80%

Specificity asks:

Of everyone who does NOT have the disease, how many did the test correctly identify?

Specificity = TN ÷ (TN + FP)

= 792 ÷ (792 + 88)

= 792 ÷ 880

= 90%

Sensitivity → disease present → true positives

Specificity → disease absent → true negatives

At a community picnic, 240 people ate potato salad. During the next 24 hours, 72 of those people developed vomiting and diarrhea.

What is the attack rate among people who ate the potato salad?

A. 20%
B. 30%
C. 33%
D. 72%

Answer: B — 30%

Rationale: Attack rate measures the proportion of exposed people who become ill. Your lecture specifically connects attack rates with infectious-disease outbreaks.

72 ÷ 240 × 100 = 30%

So, 30% of the exposed group became ill.

Remember:
Attack rate = ill exposed people ÷ total exposed people × 100

During one year, 800 people are diagnosed with a particular disease. Of those individuals, 120 die from that disease.

What is the case fatality rate?

A. 6.7%
B. 12%
C. 15%
D. 80%

Answer: C — 15%

Rationale: Case fatality looks specifically at:

Deaths from the disease ÷ people who have the disease

120 ÷ 800 × 100 = 15%

This means 15% of people diagnosed with the disease died from it. Your lecture defines case fatality as deaths due to a specified disease divided by the number of cases of that disease.

Do not use the total community population as the denominator.

Before a workplace exercise program, 20% of workers developed back pain. After the intervention, only 8% developed back pain.

What is the relative risk reduction?

A. 12%
B. 40%
C. 60%
D. 150%

Answer: C — 60%

Rationale: First calculate relative risk:

RR = 8% ÷ 20% = 0.40

Then:

Relative Risk Reduction = 1.0 − 0.40

= 0.60 = 60%

Your lecture uses this exact framework: when risk falls from 20% to 8%, the relative risk is 0.40 and the relative risk reduction is 60%.

Be careful with absolute versus relative reduction:

Absolute risk reduction: 20% − 8% = 12 percentage points

Relative risk reduction: 60%

A screening test is used on 200 patients who actually have a disease. The test correctly identifies 170 patients as positive, while 30 patients receive a negative result.

What is the sensitivity of the test?

A. 15%
B. 70%
C. 85%

Answer: C — 85%

Rationale: Sensitivity asks:

Of everyone who actually HAS the disease, how many tested positive?

Sensitivity = TP ÷ (TP + FN) × 100

= 170 ÷ (170 + 30) × 100
= 170 ÷ 200 × 100
= 85%

A test with poor sensitivity will miss more people who truly have the disease, producing more false negatives.

During one year, a county reports 5,000 total deaths from all causes. Of these deaths, 750 are due to heart disease.

What is the proportional mortality due to heart disease?

A. 6.7%
B. 15%
C. 25%
D. 75%

Answer: B — 15%

Rationale: Proportional mortality compares:

Deaths from one specific cause ÷ deaths from all causes

750 ÷ 5,000 × 100 = 15%

So 15% of all deaths in that county were due to heart disease.

Your lecture distinguishes proportional mortality from case fatality: proportional mortality compares one cause of death with all deaths, while case fatality compares deaths from a disease with people who have that disease

A PHN investigates whether exposure to a contaminated water source is associated with gastrointestinal illness.

Among 400 exposed residents, 80 become ill.
Among 500 unexposed residents, 25 become ill.

What is the relative risk?

A. 0.25
B. 2.0
C. 4.0
D. 5.0

Answer: C — 4.0

Rationale: First calculate the risk in each group.

Exposed:

80 ÷ 400 = 20%

Unexposed:

25 ÷ 500 = 5%

Relative Risk:

20% ÷ 5% = 4.0

This means the exposed residents had 4 times the risk of gastrointestinal illness compared with the unexposed residents.

Your lecture defines relative risk as:

Incidence in exposed ÷ incidence in non-exposed

A RR of 1 = same risk, >1 = greater risk with exposure, and <1 = less risk with exposure

A PHN studies the effect of exposure to secondhand smoke.

Among 300 exposed people, 75 develop respiratory disease.
Among 300 unexposed people, 30 develop respiratory disease.

What is the attributable risk associated with secondhand smoke exposure?

A. 10%
B. 15%
C. 25%
D. 45%

Answer: B — 15%

Rationale:

Risk in exposed:

75 ÷ 300 = 25%

Risk in unexposed:

30 ÷ 300 = 10%

Attributable Risk:

25% − 10% = 15%

So, 15 percentage points of disease risk are attributable to the exposure.

Your lecture defines attributable risk as the incidence in the exposed group minus the incidence in the non-exposed group.

A town has 4,000 residents. At the beginning of the year, 500 residents already have hypertension. During the year, 175 new cases of hypertension are diagnosed.

What is the incidence of hypertension during that year?

A. 4.4%
B. 5.0%
C. 12.5%
D. 16.9%

Answer: B — 5.0%

Rationale: Incidence looks at new cases among people who were actually at risk of becoming new cases.

Population at risk:

4,000 − 500 = 3,500

Incidence:

175 ÷ 3,500 × 100 = 5%

So, the incidence is 5%.

Your lecture defines incidence as new cases ÷ population at risk and notes that it reflects the risk of developing a disease or condition.

A public health nurse is developing a community action plan to prevent the spread of West Nile Virus. Which intervention specifically disrupts the relationship between the environment and the vector in the epidemiological triangle?

A) Educating residents to wear long-sleeved shirts and pants when spending time outdoors. B) Distributing free mosquito netting for families to use over beds and strollers. C) Organizing a neighborhood cleanup to identify and drain areas of standing water. D) Administering prophylactic antiviral medications to high-risk older adults.

Rationale: C is correct. West Nile Virus is a vector-borne disease transmitted by mosquitoes. Draining standing water removes the breeding grounds for the mosquitoes, which directly disrupts the link between the environment and the vector.

• A and B are incorrect because wearing long sleeves and using mosquito nets disrupt the relationship between the vector (mosquito) and the host (human) by preventing the bite.

• D is incorrect because medications or vaccines disrupt the relationship between the agent and the host by boosting immunity or fighting the pathogen.

A patient is exposed to a highly contagious communicable disease and is administered immune globulin at the local health department to prevent severe illness. The nurse understands that this treatment provides which type of immunity?

A) Active artificial immunity

B) Passive artificial immunity

C) Active natural immunity

D) Passive natural immunity

ationale: B is correct. Passive artificial immunity occurs when an individual receives antibodies (such as immune globulin products) that were made elsewhere, providing immediate but temporary protection.

• A is incorrect because active artificial immunity occurs when a person receives a vaccination, prompting their own immune system to make a response.

• C is incorrect because active natural immunity occurs when a person is exposed to the actual infection and their body builds its own antibodies.

• D is incorrect because passive natural immunity occurs when maternal antibodies are passed to an infant through the placenta or breast milk.

A school nurse is managing an outbreak of measles. A concerned parent asks why the disease spread so quickly through the classroom before any of the children even looked sick. What is the best epidemiological explanation the nurse can provide?

A) The children were likely infected by a contaminated fomite, which completely bypasses the standard incubation period.

B) The disease is currently endemic to the school, meaning the students' immune systems were overwhelmed immediately upon exposure.

C) The herd immunity threshold dropped below 95%, causing the infectious agent to become more virulent.

D) The communicable period for the disease overlaps with the incubation period, meaning children were contagious before showing any symptoms.

Rationale: D is correct. The incubation period is the time between invasion of the agent and the first signs or symptoms, while the communicable period is the interval when the agent can be transferred to others. These periods can overlap, meaning a host can be highly contagious before they even realize they are sick, which makes containment difficult.

• A is incorrect because a fomite is an inanimate object (like a toy or bedrail), and exposure to a fomite does not bypass a disease's physiological incubation period.

• B is incorrect because an endemic disease is one that regularly occurs in a community, not a term describing immediate immune system failure.

• C is incorrect because while measles does require a ~95% herd immunity threshold to prevent outbreaks, a drop in coverage allows the disease to spread; it does not change the actual virulence or physiological incubation of the agent itself.

A local health department reports that the community's MMR (Measles, Mumps, and Rubella) vaccination coverage for kindergartners has dropped to 90%. Shortly after, a measles outbreak occurs. A local politician asks the public health nurse why an outbreak happened if 9 out of 10 children are vaccinated. What is the most accurate response?

A) "Measles is highly contagious and requires a herd immunity threshold of about 95% to prevent sustained transmission."

B) "The measles vaccine only provides passive artificial immunity, which wears off quickly and leaves the 90% vulnerable."

C) "Measles is a vector-borne disease, so vaccination rates do not impact community spread as much as mosquito control does."

D) "An outbreak is defined as a global spread of disease, which occurs regardless of local kindergarten vaccination rates."

Rationale: A is correct. Herd immunity protects a community by making transmission unlikely, but diseases differ in how easily they spread. Measles is highly contagious and requires a community immunity level of about 95% to prevent outbreaks. Because the rate dropped to 90%, the herd immunity threshold was not met.

• B is incorrect because the MMR vaccine provides active artificial immunity, not passive artificial immunity.

• C is incorrect because measles is transmitted via the respiratory route, not by a vector.

• D is incorrect because global spread is the definition of a pandemic, whereas an outbreak is a sudden, often localized increase in cases

The CDC notes a sudden, significant increase in cases of a specific respiratory virus across several states in the Midwest. The number of cases is much greater than what is normally expected for this time of year. How should the public health nurse classify this event?

A) An endemic

B) A pandemic

C) An epidemic

D) A localized outbreak

Rationale: C is correct. An epidemic is defined as a situation where the number of cases is greater than normally expected and impacts multiple communities, a region, or a country.

• A is incorrect because an endemic disease is one that regularly occurs within an area or community at an expected baseline level.

• B is incorrect because a pandemic is an epidemic that has spread globally.

• D is incorrect because an outbreak typically refers to a sudden increase that is more localized (e.g., within a single school, nursing home, or town), whereas this scenario spans several states.

A factory worker develops a musculoskeletal injury from repetitive lifting. The factory has mandatory 12-hour shifts and inflexible management policies regarding break times. According to the epidemiological model applied to occupational health, the shift work and inflexible management policies represent which component?

A) The Host

B) The Agent

C) The Environment

D) The Vector

Rationale: C is correct. In the occupational health epidemiological model, the Environment encompasses all external conditions that influence the interaction between the host and agent, specifically including workplace conditions like temperature extremes, crowding, shift work, and inflexible management styles.

• A is incorrect because the Host refers to the worker and their individual susceptibility factors, such as age, gender, illness, work practices, and lifestyle habits.

• B is incorrect because the Agent refers to the actual occupational exposures or hazards (e.g., biological, chemical, physical, or mechanical/ergonomic factors like repetitive lifting).

• D is incorrect because a vector (a living organism that transmits disease) is not applicable to this scenario.

An occupational health nurse is conducting pre-employment vision and hearing screenings for newly hired manufacturing employees. This activity represents which level of prevention in the workplace?

A) Primary prevention

B) Secondary prevention

C) Tertiary prevention

D) Aggregate prevention

Rationale: B is correct. Secondary prevention in occupational health involves health screenings, which specifically include pre-employment physical exams, vision tests, hearing tests, drug and alcohol screenings, and monitoring employee health for trends.

• A is incorrect because primary prevention involves preventing hazards before they occur, such as providing immunizations, assuring accommodations for pregnant employees, and evaluating workplace risks.

• C is incorrect because tertiary prevention focuses on restoring health and managing existing conditions, such as case management for injured employees, disability management, and assessing fitness to return to work.

• D is incorrect because aggregate prevention is not a standard epidemiological level of prevention

A 72-year-old patient presents to the community clinic with a chronic cough and shortness of breath. The occupational health nurse takes a comprehensive history, specifically asking about the patient's past jobs in construction and manufacturing. According to the epidemiological model applied to occupational health, the patient's status as a retiree is considered which of the following?

A) A biological agent B) An environmental condition C) A masked risk factor of the host D) A psychosocial hazard

Rationale: C is correct. In the occupational health epidemiological model, the "Host" refers to the worker. When conducting an occupational health assessment, the nurse must look for "masked risks," such as the patient being a retiree or a housewife, because past hazardous exposures may not manifest as illness until years later.

• A is incorrect because biological agents are infectious hazards (like bacteria or viruses) in the workplace.

• B is incorrect because environmental conditions refer to the external workplace setting, such as temperature, crowding, or shift work.

• D is incorrect because a psychosocial hazard refers to current psychological stress or job strain

A public health nurse is performing START triage at the scene of a mass casualty event. The nurse assesses a victim who is unable to walk. The victim is breathing spontaneously with a respiratory rate of 24 breaths per minute. The nurse notes a capillary refill time of 3 seconds, and the victim is able to follow simple commands. How should the nurse tag this victim?

A) Priority 1 (Immediate / Red)

B) Priority 2 (Urgent / Yellow)

C) Priority 3 (Delayed / Green)

D) Dead (Black)

Rationale: A is correct. According to the START triage algorithm, a patient is tagged as Priority 1 (Immediate / Red) if they meet any of the critical thresholds for respirations, perfusion, or mental status. Although this patient has a normal respiratory rate (10-29) and can follow commands, their capillary refill is 3 seconds (which is 2 seconds or more). Therefore, they are categorized as Red/Immediate.

• B is incorrect because to be Priority 2 (Yellow), the patient must have normal respirations (10-29), normal perfusion (cap refill <2 seconds), and the ability to follow commands.

• C is incorrect because Priority 3 (Green) is reserved strictly for those who are walking (the "walking wounded").

• D is incorrect because the Black tag is reserved for those who are not breathing even after an airway maneuver has been attempted

A public health nurse is utilizing the START triage method following an industrial explosion. A victim is found lying on the ground and cannot walk. The victim is breathing at a rate of 18 breaths per minute, has a capillary refill time of 1 second, but is deeply confused and unable to follow the nurse's command to squeeze their hand. What is the appropriate triage tag for this victim?

A) Priority 1 (Immediate / Red)

B) Priority 2 (Urgent / Yellow)

C) Priority 3 (Delayed / Green)

D) Dead (Black)

Rationale: A is correct. Under START triage, if a non-walking victim has a normal respiratory rate (10-29 breaths per minute) and normal perfusion (capillary refill <2 seconds), the nurse must next assess mental status. Because this victim cannot follow simple commands, they are immediately tagged as Priority 1 (Immediate / Red).

• B is incorrect because a Priority 2 (Yellow) tag requires the patient to have normal respirations, normal perfusion, and the ability to follow commands.

• C is incorrect because Priority 3 (Green) is strictly for the walking wounded.

• D is incorrect because the Black tag is for victims who are not breathing even after their airway is manually opened.

A public health nurse arrives at the scene of a building collapse and begins START triage. A victim is found unresponsive on the ground and is not breathing. The nurse manually opens the victim's airway, and the victim immediately takes a gasping breath. What is the correct triage tag for this victim?

A) Priority 1 (Immediate / Red) B) Priority 2 (Urgent / Yellow) C) Priority 3 (Delayed / Green) D) Dead (Black)

Rationale: A is correct. Under the START algorithm, if a victim is not breathing, the first step is to open the airway. If breathing is restored after the airway maneuver, the victim is immediately tagged as Priority 1 (Immediate / Red).

• B is incorrect because a Priority 2 (Yellow) tag requires the patient to be breathing spontaneously with a normal rate, have normal perfusion, and follow commands.

• C is incorrect because Priority 3 (Green) is only for victims who are walking.

• D is incorrect because a Dead (Black) tag is only given if the victim remains pulseless and apneic after the airway has been manually opened.

During a mass casualty incident, a nurse evaluates a victim who was thrown to the ground and cannot stand up. The victim's respiratory rate is 20 breaths per minute, capillary refill time is 1.5 seconds, and the victim accurately follows the nurse's command to wiggle their toes. How should this victim be categorized?

A) Priority 1 (Immediate / Red)

B) Priority 2 (Urgent / Yellow)

C) Priority 3 (Delayed / Green)

D) Dead (Black)

Rationale: B is correct. To receive a Priority 2 (Urgent / Yellow) tag, a non-walking victim must pass all three objective assessments: respirations must be between 10 and 29, circulation must be adequate (capillary refill <2 seconds or pulse <120), and the victim must be able to follow commands. Because this patient meets all these normal parameters but cannot walk, they are classified as Yellow.

• A is incorrect because the patient does not fail any of the thresholds (respirations, circulation, or mental status) that would trigger a Priority 1 (Red) tag.

• C is incorrect because Priority 3 (Green) is exclusively for the walking wounded; since the victim cannot stand or walk, they cannot be Green.

• D is incorrect because the victim is alive and breathing

First responders are triaging victims following a train derailment. A victim approaches the nurse walking under their own power. The victim is holding a visibly deformed, fractured arm and has a moderately bleeding laceration on their forehead. According to the START triage method, what tag should this victim receive?

A) Priority 1 (Immediate / Red) B) Priority 2 (Urgent / Yellow) C) Priority 3 (Delayed / Green) D) Priority 4 (Minor / White)

Rationale: C is correct. The very first step in the START triage algorithm is to assess movement. If the victim is walking, they are automatically categorized as Priority 3 (Delayed / Green), regardless of how visible or painful their injuries (such as a broken arm or bleeding laceration) may appear.

• A and B are incorrect because any victim who can walk is directed to a staging area as a Priority 3 (Green), bypassing the immediate assessment of respiratory rate, perfusion, and mental status used to determine Red and Yellow tags.

• D is incorrect because START triage utilizes a 4-color system: Red, Yellow, Green, and Black; there is no "White" tag in this algorithm.

A victim of a stadium collapse is lying on the ground holding their abdomen and states they cannot stand up. The nurse assesses the victim and finds a respiratory rate of 22 breaths per minute and a radial pulse of 110 beats per minute. When asked, the victim correctly squeezes the nurse's hand. How should the nurse tag this victim?

A) Priority 1 (Immediate / Red) B) Priority 2 (Urgent / Yellow) C) Priority 3 (Delayed / Green) D) Dead (Black)

Rationale: B is correct. To be tagged as Priority 2 (Urgent / Yellow), a non-walking victim must pass three specific assessments. Their respiratory rate must be normal (10-29), their circulation must be adequate (pulse less than 120 or cap refill less than 2 seconds), and they must be able to respond to commands. This victim meets all three of these parameters (respirations 22, pulse 110, follows commands) but cannot walk, so they are tagged Yellow.

• A is incorrect because the victim does not fail any of the assessments (respirations >29 or <10; pulse >120; unable to follow commands) that would require a Red tag.

• C is incorrect because Priority 3 (Green) requires the victim to be able to walk.

• D is incorrect because the victim is conscious and breathing.

A public health nurse is organizing a community initiative to provide free bicycle helmets and safety education to children at a local middle school. This intervention represents which level of prevention?

A) Primary prevention B) Secondary prevention C) Tertiary prevention D) Universal prevention

Rationale: A is correct. Primary prevention targets well populations with the goal of protecting against threats to health, preventing problems from occurring, and reducing potential susceptibility. Distributing helmets to healthy children to prevent future head injuries is a clear example of primary prevention.

• B is incorrect because secondary prevention targets those with early or asymptomatic disease and focuses on early identification, such as rapid screening tests.

• C is incorrect because tertiary prevention targets individuals who already have a disease or condition to prevent worsening and restore functioning.

• D is incorrect because "universal prevention" is not one of the standard three levels of epidemiological prevention

A community health nurse is collecting data about the local community concerning a recognized health issue. The nurse wants to start with a primary source. Which source would be considered primary data?

A. World Health Organization
B. Community members
C. State health department
D. Other community health nurses

Answer: B — Community members

Rationale: Primary data is information collected directly from the community of interest, such as interviews, surveys, or direct observations. Data from organizations, databases, or health departments is considered secondary data because it was collected by someone else.