Epidemiology Practice Questions

Q: All of the following diseases can be transmitted during the incubation period except?

Tuberculosis. **Explanation:** The core concept tested here is the **Period of Communicability**, which refers to the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person. **Why Tuberculosis is the correct answer:** In **Tuberculosis (TB)**, transmission does not occur during the incubation period. TB becomes communicable only when the disease becomes **active** (clinically manifest), particularly in pulmonary TB where the patient is coughing up bacilli (Sputum positive). Latent TB infection is not infectious. **Analysis of Incorrect Options:** In many viral and some bacterial respiratory infections, the period of communicability starts *before* the onset of clinical symptoms (during the late incubation period): * **Measles:** Highly infectious during the prodromal stage. It is communicable from **4 days before to 5 days after** the appearance of the rash. * **Hepatitis A:** The maximum infectivity occurs during the latter half of the incubation period, usually **2 weeks before** the onset of jaundice. * **Pertussis:** Most infectious during the **catarrhal stage** (the end of the incubation period), before the characteristic "whoop" begins. **High-Yield NEET-PG Pearls:** * **Incubation Period vs. Generation Time:** Generation time is the interval between receipt of infection and maximal infectivity. If generation time is shorter than the incubation period (as in Measles or Hep A), the disease spreads rapidly before symptoms appear. * **Diseases NOT infectious during incubation:** TB, Typhoid, and Syphilis. * **Shortest Incubation Period:** Influenza (1–3 days), Cholera (1–5 days). * **Longest Incubation Period:** Leprosy (3–5 years), Filariasis (8–16 months).

Q: Which of the following is NOT an example of an epizootic?

Malaria. ### Explanation The key to answering this question lies in understanding the terminology used to describe disease patterns in animal populations versus human populations. **Why Malaria is the Correct Answer:** **Malaria** is an **anthroponosis**, meaning it is a disease that primarily affects humans and is transmitted from human to human (via the Anopheles mosquito). It is not an animal disease. An **Epizootic** is defined as an outbreak (epidemic) of an infectious disease in an **animal population** that rises to levels clearly in excess of normal expectancy. Since Malaria does not occur as an epidemic among animals, it cannot be classified as an epizootic. **Analysis of Incorrect Options:** * **Brucellosis:** This is a classic zoonotic disease affecting cattle, goats, and sheep. Outbreaks in these animal populations are termed epizootics. * **Anthrax:** Caused by *Bacillus anthracis*, it primarily affects herbivores. Rapid spreads in livestock are common examples of epizootic events. * **Rabies:** This is an enzootic disease (constantly present in animals) that can frequently flare up into epizootic proportions among wild or domestic animal populations (e.g., foxes, dogs). **High-Yield NEET-PG Pearls:** * **Epizootic:** An epidemic in animals (e.g., Anthrax, Brucellosis, Bird Flu). * **Enzootic:** An endemic in animals; present at a constant low level (e.g., Anthrax in certain soils, Rabies in bats). * **Epornitic:** An epidemic in bird populations. * **Zoonosis:** A disease naturally transmitted from vertebrate animals to humans (e.g., Rabies, Plague). * **Anthroponosis:** A disease where the reservoir is human (e.g., Malaria, Typhoid, Measles).

Q: Bias in which variation occurs due to different diseases being treated in different hospitals?

Berksonian bias. ### Explanation **Berksonian Bias (Admission Rate Bias)** The correct answer is **Berksonian bias**. This is a type of selection bias that occurs in hospital-based case-control studies. It arises because the probability of hospitalization for patients with two conditions (exposure and disease) is different from those with only one. Since different hospitals specialize in different diseases or have varying admission criteria, the sample becomes unrepresentative of the general population. This creates a spurious (false) association between the exposure and the disease. **Analysis of Incorrect Options:** * **Neyman Bias (Prevalence-Incidence Bias):** This occurs when there is a gap between the onset of a disease and the selection of study subjects. It typically excludes "silent" cases, quick recoveries, or fatal cases (selective survival), leading to an over-representation of chronic or stable cases. * **Attention Bias (Hawthorne Effect):** This occurs when study participants alter their behavior or responses simply because they are aware they are being observed or studied. * **Recall Bias:** A type of information bias common in case-control studies where cases (diseased individuals) remember past exposures more accurately or more frequently than controls (healthy individuals). **High-Yield Clinical Pearls for NEET-PG:** * **Berksonian Bias** is the most common reason why hospital-based studies cannot be generalized to the community. * To **minimize Berksonian bias**, researchers should use community-based controls rather than hospital-based controls. * **Selection Bias** occurs during the design/sampling stage, whereas **Information Bias** occurs during the data collection stage. * **Neyman Bias** is most commonly associated with Cross-sectional and Case-control studies involving chronic diseases.

Q: What is the sex ratio?

Number of females per 1000 males. ### Explanation **1. Why Option D is Correct:** In demography and public health, the **Sex Ratio** is a key indicator used to measure the balance between males and females in a population. In the Indian context (and for the NEET-PG exam), it is defined as the **number of females per 1,000 males**. This is an "indirect ratio" where the denominator is fixed at 1,000 to provide a standardized measure for comparing different geographical regions or time periods. **2. Why Other Options are Incorrect:** * **Options A & B:** These represent the "Masculinity Proportion" or the sex ratio as defined in many Western countries (where it is often expressed as males per 100 females). However, Indian census methodology specifically uses females as the numerator. * **Option C:** While this uses the correct numerator (females), the multiplier is 100. In large-scale population studies like the Census, a multiplier of 1,000 is used to ensure precision and capture smaller demographic shifts. **3. NEET-PG High-Yield Clinical Pearls:** * **Child Sex Ratio (CSR):** Defined as the number of females per 1,000 males in the **0–6 years** age group. This is a sensitive indicator of female feticide and neglect. * **Census 2011 Data:** The overall sex ratio in India was **943** females per 1,000 males. The Child Sex Ratio was **919**. * **Highest/Lowest:** According to the 2011 Census, **Kerala** had the highest sex ratio (1084), while **Haryana** had the lowest (879) among states. * **NFHS-5 Data:** Recent National Family Health Survey (NFHS-5) trends suggest a shift, showing 1,020 females per 1,000 males, though Census data remains the primary gold standard for exam questions unless specified otherwise.

Q: In an outbreak of cholera in a village of 2000 population, 20 cases have occurred and 5 died. What is the case fatality rate?

25%. ### Explanation **1. Understanding the Correct Answer (D: 25%)** 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 it within a specified period. The formula for CFR is: $$\text{CFR} = \frac{\text{Total number of deaths due to a disease}}{\text{Total number of cases of the same disease}} \times 100$$ In this scenario: * Total deaths = 5 * Total cases = 20 * Calculation: $(5 / 20) \times 100 = \mathbf{25\%}$ **2. Why the Incorrect Options are Wrong** * **Option A (1%):** This is the **Cause-Specific Mortality Rate** (Total deaths / Total population $\times 100$), which is $(5 / 2000) \times 100 = 0.25\%$, not 1%. * **Option B (0.25%):** This represents the **Mortality Rate** (or Cause-Specific Death Rate) for the village. It incorrectly uses the total population as the denominator instead of the number of cases. * **Option C (5%):** This is the **Attack Rate** (Total cases / Total population at risk $\times 100$), which is $(20 / 2000) \times 100 = 1\%$. 5% is a mathematical distractor. **3. High-Yield Clinical Pearls for NEET-PG** * **CFR vs. Mortality Rate:** CFR is a **ratio** (though expressed as a percentage) and measures the **killing power** of a disease. Mortality rate is a **rate** and measures the risk of dying in the general population. * **Denominator:** Always remember that for CFR, the denominator is the **number of cases**, not the total population. * **Cholera Fact:** Without treatment, the CFR of Cholera can be as high as 50%; with prompt rehydration therapy, it can be reduced to less than 1%. * **Disease Severity:** CFR is the best indicator of the virulence of an infectious agent and the efficacy of treatment.

Q: Regarding point source epidemics, which statement is true?

Rapid rise and fall in cases. ### Explanation In epidemiology, a **Point Source Epidemic** occurs when a group of susceptible individuals is exposed to a specific pathogen or toxin simultaneously or over a very short period. **1. Why Option A is Correct:** Because the exposure is simultaneous and brief, all cases occur within one incubation period of the disease. This results in a characteristic **"log-normal" epidemic curve** featuring a **rapid rise and a rapid fall** in the number of cases. The curve is typically positively skewed. **2. Analysis of Incorrect Options:** * **Option B (Caused only by infections):** Incorrect. Point source epidemics can be non-infectious, such as the Bhopal Gas Tragedy (toxic chemical leak) or Minamata disease (mercury poisoning). * **Option C (Characterized by explosive spread):** While the rise is rapid, "explosive spread" is a term more accurately associated with **Common Source, Continuous Exposure** or **Propagated Epidemics** where the source remains active or spreads person-to-person. * **Option D (High secondary attack rate):** Incorrect. A hallmark of point source epidemics is that there is **no person-to-person transmission**. Therefore, the secondary attack rate is typically **zero**. High secondary attack rates are characteristic of Propagated (Communicable) epidemics. **3. NEET-PG High-Yield Pearls:** * **Epidemic Curve:** Look for a sharp peak and a single incubation period. * **Secondary Attack Rate (SAR):** Always zero in a pure point source epidemic (e.g., food poisoning at a single wedding). * **Examples:** Food poisoning (Staphylococcal), Bhopal Gas Tragedy, Hiroshima atomic bombing. * **Key Distinction:** If the exposure continues over time (e.g., a contaminated well), it becomes a **Continuous Common Source Epidemic**, and the curve will have a plateau rather than a sharp peak.

Q: Which stage of the demographic cycle is characterized by a declining death rate while the birth rate remains high?

Death rate starts to decline which birth rate is the same. ### Explanation The **Demographic Cycle** describes the historical transition of a population from high birth and death rates to low birth and death rates as a country develops. **1. Why the Correct Answer is Right:** The stage described is **Stage 2: Early Expanding**. In this stage, the death rate begins to decline due to improvements in food supply, sanitation, and basic healthcare. However, the birth rate remains high because social norms and lack of contraception take longer to change. This gap between a high birth rate and a falling death rate leads to an **"explosive" increase** in population size. **2. Analysis of Incorrect Options:** * **Option A (Birth rate lower than death rate):** This describes **Stage 5: Declining**. Here, the population actually decreases (e.g., Germany, Hungary). * **Option B (High birth rate and high death rate):** This is **Stage 1: High Stationary**. The population remains stable because the high number of births is cancelled out by high mortality (e.g., India before 1920). * **Option D (Death rate further declines and birth rate also falls):** This is **Stage 3: Late Expanding**. While the population is still growing, the rate of growth slows down as birth rates begin to drop (e.g., India is currently in this stage). **3. High-Yield NEET-PG Pearls:** * **India’s Status:** India is currently in **Stage 3 (Late Expanding)**. * **Stage 4 (Low Stationary):** Characterized by low birth and low death rates (e.g., USA, UK). * **Key Indicator:** The "Natural Increase" of a population is the difference between the birth rate and the death rate. * **Demographic Gap:** The maximum gap between birth and death rates occurs at the end of Stage 2 and the beginning of Stage 3.

Question 1

All of the following diseases can be transmitted during the incubation period except?

Accepted Answer

Tuberculosis

Answer

Measles

Answer

Hepatitis A

Answer

Pertussis

Question 2

Which of the following is NOT an example of an epizootic?

Accepted Answer

Malaria

Answer

Brucellosis

Answer

Anthrax

Answer

Rabies

Question 3

Which of the following statements about 'total fertility rate' is true?

Accepted Answer

Indicates the approximate magnitude of completed family size.

Answer

The numerator is the number of women of childbearing age.

Answer

The numerator is the number of all live births.

Answer

The numerator is the number of married women of childbearing age.

Question 4

Bias in which variation occurs due to different diseases being treated in different hospitals?

Accepted Answer

Berksonian bias

Answer

Neyman bias

Answer

Attention bias

Answer

Recall bias

Question 5

What is the sex ratio?

Accepted Answer

Number of females per 1000 males

Answer

Number of males per 100 females

Answer

Number of males per 1000 females

Answer

Number of females per 100 males

Question 6

In an outbreak of cholera in a village of 2000 population, 20 cases have occurred and 5 died. What is the case fatality rate?

Accepted Answer

25%

Answer

1%

Answer

0.25%

Answer

5%

Question 7

In which of the following diseases is overall survival increased by a screening procedure?

Accepted Answer

Colon cancer

Answer

Prostate cancer

Answer

Lung cancer

Answer

Ovarian cancer

Question 8

Regarding point source epidemics, which statement is true?

Accepted Answer

Rapid rise and fall in cases

Answer

Caused only by infections

Answer

Characterized by explosive spread

Answer

Associated with a high secondary attack rate

Question 9

Which of the following diseases is an example of the 'iceberg phenomenon'?

Accepted Answer

Influenza

Answer

Rabies

Answer

Measles

Answer

Tetanus

Question 10

Which stage of the demographic cycle is characterized by a declining death rate while the birth rate remains high?

Accepted Answer

Death rate starts to decline which birth rate is the same

Answer

Birth rate is lower than the death rate

Answer

High birth rate and high death rate

Answer

Death rate further declines and birth rate also falls

Epidemiology — MCQs

Epidemiology — MCQs

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