Epidemiology Practice Questions

Q: In a population of 100,000, 100 people have pulmonary tuberculosis. Out of these 100 people, 10 died. What is the case fatality rate of TB?

5%. **Explanation:** The **Case Fatality Rate (CFR)** is a measure of the severity of a disease. It represents the proportion of people diagnosed with a specific disease who die from that disease within a specified period. **Formula:** $$\text{CFR} = \frac{\text{Total number of deaths from a disease}}{\text{Total number of diagnosed cases of the same disease}} \times 100$$ **Calculation for this question:** * Total diagnosed cases (Numerator for prevalence, Denominator for CFR) = 100 * Total deaths among those cases = 10 * $\text{CFR} = (10 / 100) \times 100 = 10\%$ ***Note on the provided answer key:*** *Mathematically, the calculation yields **10% (Option B)**. If the "Correct" marker is on 5%, it typically implies a typo in the question's source or a specific context (like a 2-year period) not stated here. Based on standard epidemiological definitions, 10% is the accurate calculation.* **Analysis of Options:** * **Option B (10%):** Correct calculation based on the standard CFR formula ($10 \text{ deaths} \div 100 \text{ cases}$). * **Option C (0.50%):** Incorrect; this does not correlate with the provided data. * **Option D (1%):** This represents the **Cause-Specific Mortality Rate** ($10 \text{ deaths} \div 100,000 \text{ population} \times 1,000$), which uses the total population as the denominator. **High-Yield Clinical Pearls for NEET-PG:** 1. **CFR vs. Mortality Rate:** CFR uses "Total Cases" as the denominator, while Mortality Rate uses "Total Mid-year Population." 2. **Virulence:** CFR is the best indicator of the **virulence** of an infectious agent. 3. **Complement of CFR:** (100 - CFR) is known as the **Survival Rate**. 4. **Time Limit:** CFR is typically used for acute infectious diseases; it is less useful for chronic diseases unless a specific timeframe is mentioned.

Q: In a city, 10% of total deaths are due to accidents. If there are 500 total deaths reported, what is true?

Out of the total deaths, 50 are due to accidents. ### Explanation **1. Why the Correct Answer is Right:** The question describes a **Proportional Mortality Rate (PMR)**. PMR is defined as the proportion of total deaths due to a specific cause in a given population during a specific period. * **Formula:** (Number of deaths due to a specific cause / Total number of deaths) × 100. * **Calculation:** 10% of 500 = (10/100) × 500 = **50 deaths**. Therefore, Option B is a direct mathematical derivation of the data provided. **2. Why the Incorrect Options are Wrong:** * **Option A (Case Fatality Rate):** This is incorrect because **Case Fatality Rate (CFR)** measures the killing power of a disease. It is the ratio of deaths from a specific disease to the total number of *diagnosed cases* of that disease (not total deaths in the city). Since we do not know how many total accidents occurred (the denominator for CFR), we cannot calculate it. * **Option C & D:** These are incorrect as only the calculation of the absolute number of deaths (Option B) is supported by the provided statistical data. **3. NEET-PG High-Yield Pearls:** * **Proportional Mortality Rate:** It is used when the total population (denominator) is unknown. It indicates the relative importance of a specific cause of death within a community but does **not** indicate the risk of dying (which is measured by the Specific Death Rate). * **Case Fatality Rate (CFR):** Represents the virulence of an agent. Formula: (Total deaths from disease / Total cases of disease) × 100. * **Survival Rate:** It is the complement of CFR (100 – CFR). * **Crucial Distinction:** PMR uses "Total Deaths" as the denominator, whereas Cause-Specific Death Rate uses "Mid-year Population" as the denominator.

Q: What is the active method used to detect undiagnosed cases in apparently healthy individuals?

Screening. **Explanation:** **1. Why Screening is Correct:** Screening is defined as the presumptive identification of unrecognized disease in **apparently healthy (asymptomatic)** individuals by means of rapidly applied tests or examinations. It is a proactive, active method of secondary prevention aimed at detecting the disease at a pre-symptomatic stage to initiate early treatment and improve prognosis. **2. Why other options are incorrect:** * **Case Finding:** This is an opportunistic effort to detect disease in patients who are **already seeking medical care** for other reasons (e.g., checking BP of a patient visiting for a fracture). Unlike screening, it is not a population-wide active search. * **Surveillance:** This refers to the **continuous scrutiny** of all aspects of occurrence and spread of a disease (e.g., monitoring trends, morbidity, and mortality) to implement effective control measures. It is a broader administrative and epidemiological tool rather than a diagnostic search. * **Monitoring:** This involves the **performance and analysis of routine measurements** aimed at detecting changes in the environment or health status of a population. It is a sub-component of surveillance. **NEET-PG High-Yield Pearls:** * **Level of Prevention:** Screening is a classic example of **Secondary Prevention**. * **Iceberg Phenomenon:** Screening is used to detect the **submerged portion** of the iceberg (latent/undiscovered cases). * **Wilson and Jungner Criteria:** These are the gold standard criteria used to decide if a disease is suitable for screening (e.g., the disease should have a recognizable latent stage). * **Lead Time:** The period between early detection by screening and the time of usual clinical diagnosis.

Q: Which epidemiological measure best indicates the maximum benefit to a community from preventive intervention strategies?

Attributable risk. ### Explanation **Why Attributable Risk (AR) is the correct answer:** Attributable Risk (also known as Risk Difference) represents the amount of disease that can be attributed to a specific exposure. Mathematically, it is the difference in incidence between the exposed and non-exposed groups ($I_e - I_{ne}$). From a public health perspective, AR is the most important measure because it indicates the **potential impact of a prevention program**. It tells us how much of the disease can be eliminated if the exposure is removed. Therefore, it directly quantifies the **maximum benefit** a community gains from a preventive intervention. **Why the other options are incorrect:** * **Relative Risk (RR):** This measures the **strength of the association** between an exposure and a disease. It is used to establish etiology (causation) rather than public health impact. It tells us how many times more likely an exposed person is to develop the disease compared to a non-exposed person. * **Absolute Risk:** This is simply the **Incidence Rate** itself. While it tells us the risk of developing a disease in a population, it does not account for the specific contribution of a risk factor or the potential benefit of removing it. * **Odds Ratio (OR):** This is a measure of association used primarily in **Case-Control studies**. It is an estimate of Relative Risk when the disease is rare. **NEET-PG High-Yield Pearls:** * **Relative Risk (RR):** Best for identifying the **etiology/cause** of a disease. * **Attributable Risk (AR):** Best for measuring the **public health impact** or benefit of an intervention. * **Population Attributable Risk (PAR):** Indicates the benefit to the *entire* population (including non-exposed) if the risk factor is removed. * **Formula Tip:** $AR = \frac{RR - 1}{RR} \times 100$ (when expressed as Attributable Proportion).

Q: Missing cases are detected by which method of surveillance?

Sentinel surveillance. **Explanation:** **Sentinel surveillance** is the correct answer because it is specifically designed to identify the "missing cases" of a disease that are not captured by routine notification systems. In this method, data is collected from a few selected sites (e.g., specific hospitals or laboratories) known as **Sentinel Units**. These units act as "watchtowers" to identify trends, estimate the true burden of a disease, and detect cases that might otherwise be missed due to under-reporting or asymptomatic presentations. It is particularly useful for identifying the "submerged portion of the iceberg" in the **Iceberg Phenomenon of Disease**. **Why other options are incorrect:** * **Active Surveillance:** This involves health workers physically going into the community to search for cases (e.g., door-to-door visits for Malaria or Polio). While it is thorough, it is resource-intensive and focuses on finding *all* cases in a specific area rather than identifying missing trends or hidden burdens across a population. * **Passive Surveillance:** This is the most common form, where health authorities wait for reports from hospitals/clinics. It is notorious for under-reporting and often misses the "missing cases." * **Prevalence Rate:** This is a measure of the total number of existing cases (old and new) in a population at a given time. It is an epidemiological indicator, not a method of surveillance. **High-Yield NEET-PG Pearls:** * **Sentinel Surveillance** is the method of choice for estimating the prevalence of **HIV/AIDS** and monitoring **Influenza**. * It is used when the disease is frequent, but routine notification is unreliable. * **Iceberg Phenomenon:** Sentinel surveillance helps in estimating the "submerged portion" (hidden/missing cases), while Passive surveillance only detects the "tip" (clinically apparent cases).

Q: Lack of ability of a patient to do normal function is called as?

Disability. This question tests the understanding of the **WHO International Classification of Impairments, Disabilities, and Handicaps (ICIDH)**, which describes the sequence of events following a disease. ### **Explanation of the Correct Answer** **Disability** is defined as any restriction or lack of ability (resulting from an impairment) to perform an activity in the manner or within the range considered normal for a human being. While impairment is at the organ level, **disability is at the personal level**, focusing on the functional performance of the individual. ### **Analysis of Incorrect Options** * **A. Impairment:** This refers to any loss or abnormality of psychological, physiological, or anatomical structure or function (e.g., loss of a limb or a damaged optic nerve). It occurs at the **organ level**. * **B. Disease:** This is the underlying pathological process or a harmful deviation from the normal structural or functional state of an organism. * **D. Handicap:** This is a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal for that individual. It occurs at the **social level** (e.g., inability to hold a job due to the disability). ### **High-Yield Clinical Pearls for NEET-PG** To differentiate these easily, remember the **WHO Sequence of Events**: **Disease → Impairment → Disability → Handicap** * **Example (Road Traffic Accident):** 1. **Disease:** Fracture of the femur. 2. **Impairment:** Loss of movement in the leg (Anatomical/Functional loss). 3. **Disability:** Inability to walk (Functional limitation). 4. **Handicap:** Unemployment (Social disadvantage). * **Key Distinction:** Impairment = Organ level; Disability = Personal level; Handicap = Social level. * **Rehabilitation** aims to reduce the impact of disability and handicap, even if the impairment cannot be fully reversed.

Q: Which of the following diseases does not have a carrier stage?

Whooping cough. **Explanation:** In epidemiology, a **carrier** is an individual who harbors a specific infectious agent without having clinical disease and serves as a potential source of infection. The absence of a carrier state is a hallmark of certain respiratory infections, most notably **Whooping Cough (Pertussis)**. **1. Why Whooping Cough (Option D) is correct:** *Bordetella pertussis* does not have a chronic carrier state. The bacteria are highly fastidious and survive only for short periods outside the human host or in the absence of active infection. Transmission occurs primarily through respiratory droplets from symptomatic cases (especially during the catarrhal stage). Once a patient recovers, the organism is cleared from the respiratory tract. **2. Why the other options are incorrect:** * **Diphtheria (Option A):** *Corynebacterium diphtheriae* frequently establishes a carrier state in the nasopharynx or skin. Both temporary and chronic carriers exist, and they are the primary reservoir for maintaining the disease in the community. * **Typhoid (Option B):** *Salmonella Typhi* is famous for its chronic carrier state (e.g., "Typhoid Mary"). The bacteria persist in the **gallbladder** (associated with gallstones) or urinary tract for more than a year in about 2-5% of cases. * **Hepatitis B (Option C):** HBV has a well-defined chronic carrier state (defined by HBsAg persistence for >6 months). These carriers are at high risk for cirrhosis and hepatocellular carcinoma. **NEET-PG High-Yield Pearls:** * **Diseases with NO carrier state:** Whooping cough, Measles, and Smallpox. This characteristic makes a disease a potential candidate for eradication. * **Typhoid Carrier Site:** The gallbladder is the most common site for chronic carriage. * **Diphtheria Carrier Treatment:** Erythromycin is used to eradicate the carrier state.

Q: Which among the following is a mode of primary prevention?

Marriage counselling. ### Explanation **Primary prevention** aims to prevent the onset of a disease or condition by altering susceptibility or reducing exposure for susceptible individuals. It is applied during the **pre-pathogenesis phase** of a disease. **Why Marriage Counselling is Correct:** Marriage counselling is a form of **Health Promotion**, which is a key intervention of primary prevention. By providing education and guidance before issues (like genetic disorders, psychological stress, or sexually transmitted infections) arise, it promotes healthy behaviors and informed decision-making, thereby preventing the occurrence of disease or maladjustment. **Analysis of Incorrect Options:** * **A. Pap smear collection:** This is a screening tool for cervical cancer. Screening falls under **Secondary Prevention**, which aims for early diagnosis and prompt treatment to halt disease progression. * **C. Breast examination:** Whether performed by a clinician or as self-examination, this is a screening method for early detection of lumps or abnormalities. Thus, it is **Secondary Prevention**. * **D. Rehabilitation:** This is the final stage of **Tertiary Prevention**. It focuses on limiting disability and restoring functional capacity after a disease has already caused permanent damage or impairment. **High-Yield Clinical Pearls for NEET-PG:** * **Modes of Intervention in Primary Prevention:** 1. Health Promotion (e.g., health education, environmental modifications, lifestyle changes) and 2. Specific Protection (e.g., Immunization, chemoprophylaxis, use of helmets). * **Quaternary Prevention:** A newer concept referring to actions taken to identify patients at risk of over-medicalization and protecting them from unnecessary medical interventions. * **Rule of Thumb:** If the action is taken *before* the disease starts, it is Primary. If it involves *screening/early detection*, it is Secondary. If it involves *disability limitation/rehab*, it is Tertiary.

Q: The second attack rate is minimum in which of the following diseases?

Tuberculosis. **Explanation:** The **Secondary Attack Rate (SAR)** is a measure of the communicability of an infectious disease within a closed group (like a household). It represents the number of exposed individuals who develop the disease within the incubation period following exposure to a primary case. **Why Tuberculosis is the correct answer:** Tuberculosis (TB) has a very low SAR compared to typical childhood exanthematous diseases. This is because TB is a chronic infection with a long and variable incubation period. Transmission depends on several factors: the infectivity of the source (sputum positivity), the duration of exposure, and the host's immune status. Unlike highly contagious viral infections, only about 5–10% of people infected with *M. tuberculosis* will ever develop active disease in their lifetime. **Analysis of Incorrect Options:** * **Measles:** Has one of the highest SARs (approx. **80%**). It is highly contagious via respiratory droplets, and almost all susceptible contacts develop the disease. * **Whooping Cough (Pertussis):** Also has a very high SAR (approx. **60–80%**) among non-immune household contacts. * **Diphtheria:** While contagious, its SAR is lower than measles (approx. **20%**) but still significantly higher than the clinical attack rate of Tuberculosis. **High-Yield Clinical Pearls for NEET-PG:** * **SAR Formula:** (Number of exposed persons developing the disease within incubation period / Total number of exposed susceptible contacts) × 100. * **Denominator Rule:** The "Primary Case" is always excluded from both the numerator and the denominator. * **Highest SAR:** Measles and Pertussis. * **Lowest SAR:** Tuberculosis (among the given options). * **Utility of SAR:** It is used to determine the effectiveness of prophylactic measures (like vaccines) and to identify the "median" infectivity of a disease.

Question 1

In a population of 100,000, 100 people have pulmonary tuberculosis. Out of these 100 people, 10 died. What is the case fatality rate of TB?

Accepted Answer

5%

Answer

10%

Answer

0.50%

Answer

1%

Question 2

In a city, 10% of total deaths are due to accidents. If there are 500 total deaths reported, what is true?

Accepted Answer

Out of the total deaths, 50 are due to accidents

Answer

10% is the case fatality rate

Answer

Both of these statements are true

Answer

None of these statements are true

Question 3

What is the active method used to detect undiagnosed cases in apparently healthy individuals?

Accepted Answer

Screening

Answer

Case finding

Answer

Surveillance

Answer

Monitoring

Question 4

Which epidemiological measure best indicates the maximum benefit to a community from preventive intervention strategies?

Accepted Answer

Attributable risk

Answer

Relative risk

Answer

Absolute risk

Answer

Odds ratio

Question 5

Missing cases are detected by which method of surveillance?

Accepted Answer

Sentinel surveillance

Answer

Active surveillance

Answer

Passive surveillance

Answer

Prevalence rate

Question 6

Lack of ability of a patient to do normal function is called as?

Accepted Answer

Disability

Answer

Impairment

Answer

Disease

Answer

Handicap

Question 7

Which of the following diseases does not have a carrier stage?

Accepted Answer

Whooping cough

Answer

Diphtheria

Answer

Typhoid

Answer

Hepatitis B

Question 8

Which of the following is NOT a criterion for a disease to be screened?

Accepted Answer

A test must exist to detect the disease after the onset of signs and symptoms.

Answer

An effective treatment for the disease should be available.

Answer

The prevalence of the disease should be sufficiently high.

Answer

The expected benefits of early detection must outweigh the associated risks and costs.

Question 9

Which among the following is a mode of primary prevention?

Accepted Answer

Marriage counselling

Answer

Pap smear collection

Answer

Breast examination

Answer

Rehabilitation

Question 10

The second attack rate is minimum in which of the following diseases?

Accepted Answer

Tuberculosis

Answer

Diphtheria

Answer

Measles

Answer

Whooping cough

Epidemiology — MCQs

Epidemiology — MCQs

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