Epidemiology Practice Questions

Q: Case Fatality Rate of a disease is a measure of its

Virulence. ***Virulence*** - **Case fatality rate (CFR)** is defined as the proportion of persons with a disease who **die from that disease**. - It directly reflects the **severity** or **lethality** of a disease among those infected. - A higher CFR indicates that the disease is more **virulent**, causing a greater proportion of infected individuals to die. - CFR is the standard epidemiological measure of **virulence**. *Chronicity* - **Chronicity** refers to the **duration** of a disease, indicating whether it is long-lasting or recurrent. - It does not directly measure the disease's ability to cause death among those infected. *Endemicity* - **Endemicity** describes the **constant presence** and/or usual prevalence of a disease in a geographic area or population. - This term relates to the typical occurrence pattern, not the deadliness of the disease. *Infectivity* - **Infectivity** is the ability of an organism to **cause infection** in a susceptible host. - It measures how easily an agent can spread and establish itself, not its capacity to cause severe disease or death.

Q: "Mid-year population" is not the denominator of which mortality rate?

Proportional mortality rate. ***Proportional mortality rate*** - The **proportional mortality rate** uses the **total number of deaths from all causes** as its denominator, not the mid-year population. - It expresses the proportion of all deaths due to a specific cause, rather than a rate per population at risk. - Formula: PMR = (Deaths from specific cause / Total deaths) × 100 *Age specific death rate* - The **age-specific death rate** uses the **mid-year population of a specific age group** as its denominator to calculate the number of deaths within that group. - This allows for comparison of mortality across different age cohorts. *Crude death rate* - The **crude death rate** uses the **total mid-year population** of a given area as its denominator. - It represents the overall mortality experience of a population but does not account for age structure. *Weekly death rate* - Though not a standard epidemiological measure, if calculated, this would use the **mid-week or average population for that specific week** as its denominator. - This would measure mortality frequency over a shorter, defined period using a population base.

Q: Consider the following characteristics of biological agents : 1. Infectivity 2. Pathogenicity 3. Virulence 4. Communicability Among the above characteristics, which are used to measure the ability of biological agents to induce clinically apparent illness?

2 and 3. ***2 and 3*** - **Pathogenicity** is the ability of an infectious agent to cause disease (clinically apparent illness) in infected individuals, measured as the proportion of infected persons who develop clinical disease. - **Virulence** is the ability of an agent to produce severe disease, measured as the proportion of clinical cases that are severe or fatal. - **Both characteristics measure different aspects of the ability to induce clinically apparent illness**: pathogenicity measures whether clinical illness occurs, while virulence measures the severity of that clinical illness. - Together, they comprehensively describe an agent's capacity to produce clinically apparent disease. *2 only* - While pathogenicity does measure the ability to cause clinically apparent illness, this is incomplete. - Virulence is also a measure of the ability to induce clinically apparent illness, specifically measuring the severity spectrum of that illness. *3 only* - Virulence alone is insufficient as it only measures severity among those who are already clinically ill. - Pathogenicity is also needed to measure the ability to produce clinical illness in the first place. *1 and 2* - **Infectivity** measures the ability of an agent to enter, survive, and multiply in a host, which is a prerequisite for disease but does not measure clinical illness itself. - An agent can have high infectivity but low pathogenicity (causing mostly subclinical infections). - Only pathogenicity and virulence directly measure aspects of clinically apparent illness.

Q: "Risk ratio" is also known as:

Relative risk. ***Relative risk*** - **Risk ratio** is another term for **relative risk**, which is a measure of association between exposure to a factor and the risk of an outcome. - It compares the risk of an event in an **exposed group** to the risk of an event in an **unexposed group**. *Odds ratio* - The **odds ratio** is a measure of association that quantifies the relationship between an exposure and an outcome, often used in **case-control studies**. - It approximates the relative risk when the outcome is **rare** but is distinct in its calculation based on odds rather than risks. *Attributable risk* - **Attributable risk** (or risk difference) quantifies the **absolute difference in risk** between exposed and unexposed groups. - It represents the amount of disease incidence that can be directly attributed to the exposure. *Population attributable risk* - **Population attributable risk** is the proportion of a disease in the total population that is attributable to a specific exposure. - It considers both the **strength of the association** and the **prevalence of the exposure** in the population.

Q: Consider the following criteria for a "screening test" : 1. Disease should have a latent period 2. Condition (disease) should be rare 3. Disease should be amenable to treatment Which of the above must be satisfied before including a screening test into any programme?

1 and 3. ***1 and 3*** - A successful screening program requires the disease to have a detectable **latent period** (criterion 1) during which early intervention can be beneficial. - Furthermore, the disease must be **amenable to treatment** (criterion 3); if there's no effective treatment, early detection offers no clinical advantage. *1 only* - While a **latent period** is essential for effective screening, it is not the sole criterion; the availability of treatment is equally critical. - Screening for a disease with a latent period but no effective treatment would lead to early diagnosis without improved outcomes, causing unnecessary anxiety. *2 only* - The **rarity of a condition** (criterion 2) is generally not a prerequisite for screening; in fact, screening is often more cost-effective for more prevalent diseases. - Screening rare diseases can lead to a low positive predictive value and higher rates of false positives, making it inefficient without substantial public health impact. *1 and 2* - Although a **latent period** is necessary, screening is generally more useful and cost-effective for diseases that are common enough to warrant population-level intervention, not necessarily rare diseases. - Screening primarily aims for early intervention and improved outcomes, which are not solely dependent on rarity, but on the disease's burden and treatability.

Q: The ratio between incidences among exposed and non-exposed persons is called

Relative risk. ***Correct: Relative risk*** - This is the ratio of the **incidence of disease** in an **exposed group** to the incidence of disease in an **unexposed group**. - It quantifies the likelihood of developing the disease in the exposed group relative to the unexposed group. - **Formula:** RR = (Incidence in exposed) / (Incidence in unexposed) *Incorrect: Positive predictive value* - This statistical measure indicates the probability that a person with a **positive test result** actually has the disease. - It is not a measure of incidence comparison between exposed and unexposed populations. *Incorrect: Attributable risk* - This measures the **absolute difference** in incidence rates between exposed and unexposed groups. - It quantifies the amount of disease incidence that can be directly attributed to the exposure, not a ratio. - **Formula:** AR = (Incidence in exposed) - (Incidence in unexposed) *Incorrect: Odds ratio* - This is a measure of association between an **exposure and an outcome**, representing the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. - It is commonly used in **case-control studies** and is a ratio of odds, not directly incidence rates.

Q: Which of the following constitutes "Secondary Prevention"?

Screening Tests. ***Screening Tests (Correct)*** - **Screening tests** constitute the core of **secondary prevention**, designed to detect disease in its **early, asymptomatic stages** before clinical symptoms appear. - By identifying disease early, screening enables **prompt intervention** to prevent progression, reduce morbidity, and improve prognosis. - Examples include mammography for breast cancer, PAP smear for cervical cancer, and blood pressure screening for hypertension. *Health Education Programme* - Health education programmes are examples of **primary prevention**, which aims to **prevent disease occurrence** by promoting healthy behaviors and reducing risk factors. - These interventions target healthy individuals to maintain health and prevent disease onset, not to detect existing disease. *Using Limb Callipers* - **Limb callipers** are used for anthropometric measurements or as assistive devices for mobility in patients with disabilities. - As a measurement tool, it's used for **assessment and monitoring**, not for disease prevention. - As an assistive device, it falls under **tertiary prevention** (rehabilitation), helping patients manage existing disability. *Wearing Safety Helmets* - Wearing safety helmets is a classic example of **primary prevention**, as it aims to **prevent injuries** (head trauma) from occurring in the first place. - It is a protective measure implemented before any health event occurs, not for early disease detection.

Q: The "risk of a disease" is measured by the

Incidence Rate. ***Incidence Rate*** - The **incidence rate** directly measures the frequency of **new cases** of a disease in a population over a specified period. - It is used to estimate the **risk** or probability of developing a disease, as it quantifies how quickly people are contracting the disease within the at-risk population. - **Formula:** (Number of new cases during time period / Population at risk) × multiplier - This is the epidemiologically correct measure of disease risk. *Prevalence Rate* - The **prevalence rate** measures the **total number of existing cases** (both new and old) of a disease in a population at a specific point in time or over a period. - It reflects the **burden** of a disease, not the risk of acquiring it, as it includes individuals who may have developed the disease much earlier. - Prevalence = Incidence × Duration of disease. *Case Fatality Rate* - The **case fatality rate** (CFR) measures the **proportion of individuals diagnosed with a disease who die from that disease** within a specified period. - It reflects the **severity** or lethality of a disease among those affected, not the risk of developing the disease in the first place. - CFR is a measure of disease outcome, not disease occurrence. *Communicability Rate* - There is no standard epidemiological term exactly defined as "communicability rate"; however, related concepts include the **basic reproduction number (R₀)** and **secondary attack rate**. - These concepts describe the **spread or transmissibility of an infectious disease**, not the risk of contracting a disease from a general population perspective. - This measures transmission dynamics rather than individual risk.

Q: The use of condoms for protection against sexually transmitted diseases qualifies as

Specific protection. ***Specific protection*** - **Specific protection** involves measures aimed at preventing particular diseases by reducing exposure to their causes or by enhancing resistance against them. - Using condoms directly acts against the transmission of **sexually transmitted infections (STIs)**, thus making it a form of specific protection. *Primordial prevention* - **Primordial prevention** focuses on addressing underlying social and economic conditions that contribute to disease risk. - It targets **root causes** before risk factors for a disease even develop in the population. *Health promotion* - **Health promotion** is a broader concept that includes educational and environmental efforts to support healthy lifestyles and reduce overall disease risk. - While condom use could be part of a health promotion campaign, the act itself is a more targeted intervention. *Secondary prevention* - **Secondary prevention** involves early detection and prompt treatment of existing health problems to prevent their progression or complications. - This would include activities like **STI screening** and starting treatment after diagnosis, not preventing initial transmission.

Question 1

Case Fatality Rate of a disease is a measure of its

Accepted Answer

Virulence

Answer

Chronicity

Answer

Endemicity

Answer

Infectivity

Question 2

"Mid-year population" is not the denominator of which mortality rate?

Accepted Answer

Proportional mortality rate

Answer

Age specific death rate

Answer

Crude death rate

Answer

Weekly death rate

Question 3

Consider the following characteristics of biological agents :

1. Infectivity
2. Pathogenicity
3. Virulence
4. Communicability

Among the above characteristics, which are used to measure the ability of biological agents to induce clinically apparent illness?

Accepted Answer

2 and 3

Answer

3 only

Answer

2 only

Answer

1 and 2

Question 4

"Risk ratio" is also known as:

Accepted Answer

Relative risk

Answer

Odds ratio

Answer

Attributable risk

Answer

Population attributable risk

Question 5

Consider the following criteria for a "screening test" :

1. Disease should have a latent period
2. Condition (disease) should be rare
3. Disease should be amenable to treatment Which of the above must be satisfied before including a screening test into any programme?

Accepted Answer

1 and 3

Answer

1 only

Answer

2 only

Answer

1 and 2

Question 6

The ratio between incidences among exposed and non-exposed persons is called

Accepted Answer

Relative risk

Answer

Positive predictive value

Answer

Attributable risk

Answer

Odds ratio

Question 7

The installation and usage of sanitary latrines by general public constitutes which level of prevention?

Accepted Answer

Specific protection

Answer

Disability limitation and rehabilitation

Answer

Early diagnosis and treatment

Answer

Health promotion

Question 8

Which of the following constitutes "Secondary Prevention"?

Accepted Answer

Screening Tests

Answer

Health Education Programme

Answer

Using Limb Callipers

Answer

Wearing Safety Helmets

Question 9

The "risk of a disease" is measured by the

Accepted Answer

Incidence Rate

Answer

Prevalence Rate

Answer

Case Fatality Rate

Answer

Communicability Rate

Question 10

The use of condoms for protection against sexually transmitted diseases qualifies as

Accepted Answer

Specific protection

Answer

Primordial prevention

Answer

Health promotion

Answer

Secondary prevention

Epidemiology — MCQs

Epidemiology — MCQs

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