Epidemiology Practice Questions

Q: What is the measure of infectivity of a disease?

Secondary attack rate. ### Explanation **Secondary Attack Rate (SAR)** is the correct measure of **infectivity**. Infectivity refers to the ability of an infectious agent to invade and multiply in a host. SAR specifically measures the number of exposed persons who develop the disease within the incubation period following exposure to a primary case. * **Formula:** (Number of exposed persons developing disease / Total number of exposed susceptible contacts) × 100. * It is the best indicator of how easily a disease spreads within a closed group (e.g., a household). **Analysis of Incorrect Options:** * **A. Incidence Rate:** Measures the number of **new cases** in a population over a specific period. It indicates the **rate of occurrence** and the risk of contracting the disease, but not specifically the ease of transmission from person to person. * **B. Prevalence Rate:** Measures the **total number of cases** (old + new) existing in a population at a given time. it is used to estimate the **burden of disease** and plan for health resources. * **C. Case Fatality Rate (CFR):** Measures the **virulence** or killing power of a disease. It is the proportion of deaths among diagnosed cases (Deaths / Total Cases × 100). **High-Yield Clinical Pearls for NEET-PG:** * **Virulence:** Measured by Case Fatality Rate. * **Pathogenicity:** The ability to produce clinical disease (Ratio of clinical cases to total infected). * **Generation Time:** The interval between receipt of infection and maximal infectivity (used to track spread instead of incubation period in diseases with subclinical stages). * **SAR for Measles:** Highly infectious (~80% in susceptible households).

Q: The high stationary stage of the demographic cycle is characterized by:

High birth rate, high death rate. **Explanation:** The **Demographic Cycle** describes the stages of population growth based on the relationship between birth rates and death rates. **1. Why Option D is Correct:** The **High Stationary Stage (Stage 1)** is characterized by both a **high birth rate** and a **high death rate**. In this stage, the population remains stationary because the high number of births is cancelled out by high mortality due to poor sanitation, lack of medical facilities, and frequent epidemics. Historically, most of the world was in this stage before the industrial revolution. **2. Why the Other Options are Incorrect:** * **Option A (High birth rate, low death rate):** This describes the **Early Expanding Stage (Stage 2)**. Here, death rates begin to fall due to improved healthcare, but birth rates remain high, leading to a population explosion. * **Option B (Low birth rate, high death rate):** This is not a standard stage in the demographic cycle. A high death rate combined with a low birth rate would lead to rapid population extinction. * **Option C (Low birth rate, low death rate):** This describes the **Low Stationary Stage (Stage 4)**. The population becomes stable again, but at a much higher total level than in Stage 1. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **India’s Current Status:** India is currently in the **Late Expanding Stage (Stage 3)**, where the birth rate is falling but still exceeds the death rate. * **Stage 5 (Declining):** Characterized by a birth rate lower than the death rate (e.g., Germany, Hungary, Japan), leading to a decreasing population. * **Key Indicator:** The transition from Stage 1 to Stage 2 is usually triggered by improvements in **public health and nutrition**, while the transition from Stage 3 to Stage 4 is driven by **socio-economic changes and family planning**.

Q: Which cancer is best suited for screening procedures?

Colon cancer. **Explanation:** The suitability of a cancer for screening depends on the **Wilson and Jungner criteria**, which state that the disease must have a recognizable latent or early symptomatic stage and a natural history that is well-understood. **Why Colon Cancer is the Correct Answer:** Colon cancer is the "ideal" candidate for screening because it follows a predictable **adenoma-to-carcinoma sequence**. This progression is slow (often taking 10–15 years), providing a wide "window of opportunity" for detection. Screening methods like Colonoscopy or Fecal Immunochemical Tests (FIT) can identify and remove precancerous polyps, not just detecting cancer early but actually **preventing** its occurrence. This significantly reduces both morbidity and mortality. **Analysis of Incorrect Options:** * **Prostate Cancer:** Screening (via PSA) remains controversial due to a high rate of **overdiagnosis**. Many prostate cancers are indolent and would never cause symptoms during a patient's lifetime; treating them can lead to unnecessary complications like impotence or incontinence. * **Gastric Cancer:** While screening (endoscopy) is performed in high-prevalence areas like Japan, it is not universally recommended. The natural history is less predictable than colon cancer, and the procedure is invasive and not cost-effective for general population screening in most regions. **High-Yield Clinical Pearls for NEET-PG:** * **Lead Time:** The period between early detection by screening and the time of usual clinical diagnosis. * **Length Bias:** Screening tends to detect slowly progressing cases more easily than rapidly progressing ones. * **Best Screening Tool:** Colonoscopy is the gold standard for colon cancer; Pap smear is the classic example for Cervical Cancer (another highly "screenable" cancer). * **Iceberg Phenomenon:** Screening aims to reveal the "submerged portion" of the iceberg (undiagnosed cases) in the community.

Q: What is Incidence Rate?

It represents the number of new cases in the community. ### Explanation **Incidence Rate** is a fundamental measure of morbidity in epidemiology. It is defined as the number of **new cases** of a specific disease occurring in a defined population during a specific period of time. #### Why Option B is Correct: The core concept of incidence is the "rate of occurrence." It measures the speed at which a disease is spreading or developing. Mathematically, it is calculated as: $$\text{Incidence} = \frac{\text{Number of NEW cases during a specific period}}{\text{Population at risk during that period}} \times 1000$$ It is a longitudinal measure, meaning it requires a follow-up study (like a **Cohort Study**) to identify new events. #### Why Other Options are Incorrect: * **Option A & C:** These refer to **Prevalence**. Prevalence includes both old and new cases (Total cases) existing at a specific point or period in time. It is a cross-sectional measure. * **Option D:** The number of cured cases is not a standard epidemiological rate used to define incidence; rather, it relates to the prognosis or the effectiveness of a treatment intervention. #### High-Yield Clinical Pearls for NEET-PG: * **Study Design:** The best study design to calculate Incidence is a **Prospective Cohort Study**. * **Prevalence vs. Incidence:** Remember the formula: **Prevalence (P) = Incidence (I) × Mean Duration of disease (D)**. * **Utility:** Incidence is best for studying the **etiology (causation)** of a disease and for evaluating the efficacy of preventive programs. * **Attack Rate:** This is a type of incidence rate used specifically during **outbreaks** (expressed as a percentage). * **Denominator:** Note that the denominator for incidence only includes the "population at risk" (those who do not have the disease yet).

Q: A survey was conducted on 7,000 drivers using mobile phones and found that 700 met with an accident. In the same period, out of 3,000 drivers not using mobile phones, 30 met with an accident. Calculate the relative risk?

10. ### Explanation **1. Understanding the Correct Answer (B: 10)** Relative Risk (RR), also known as Risk Ratio, is the ratio of the incidence of a disease (or event) among an exposed group to the incidence among a non-exposed group. It is a key measure of association in **Cohort Studies**. * **Incidence in Exposed ($I_e$):** Drivers using mobile phones. $I_e = \frac{\text{Accidents}}{\text{Total Exposed}} = \frac{700}{7,000} = 0.1$ (or 10%) * **Incidence in Non-exposed ($I_ne$):** Drivers not using mobile phones. $I_ne = \frac{\text{Accidents}}{\text{Total Non-exposed}} = \frac{30}{3,000} = 0.01$ (or 1%) * **Relative Risk (RR):** $\frac{I_e}{I_ne} = \frac{0.1}{0.01} = \mathbf{10}$ This means drivers using mobile phones are 10 times more likely to meet with an accident compared to those who do not. **2. Why Other Options are Incorrect** * **Option A (5):** This would result if the incidence in the exposed group was only 0.05 (5%). * **Option C (3.99):** This is a distractor often seen in questions involving complex Odds Ratio calculations, but it is mathematically irrelevant here. * **Option D (8.33):** This might be reached if a student incorrectly uses the "Attributable Risk" formula or makes a calculation error in the denominator. **3. High-Yield Clinical Pearls for NEET-PG** * **RR = 1:** No association between exposure and outcome. * **RR > 1:** Positive association (Risk factor). * **RR < 1:** Negative association (Protective factor, e.g., vaccines). * **Study Design:** RR is calculated from **Cohort Studies** (Prospective), whereas Odds Ratio (OR) is typically calculated from **Case-Control Studies** (Retrospective). * **Attributable Risk (AR):** $I_e - I_ne$. In this case, $0.1 - 0.01 = 0.09$ (90 per 1000), representing the amount of disease prevented if the exposure is removed.

Q: Berkesonian bias refers to which of the following?

Different rates of admission to the hospital. ### Explanation **Berksonian Bias** (also known as Admission Rate Bias) is a type of selection bias that occurs specifically in **hospital-based case-control studies**. **1. Why Option A is Correct:** The bias arises because hospital patients differ from the general population. It occurs when the **probability of admission** to a hospital is different for cases and controls, often because they have multiple diseases (comorbidities). For example, if a study examines the link between respiratory disease and bone fractures using hospitalized patients, the results may show a false association because people with *both* conditions are more likely to be admitted than those with only one. This distorts the true relationship between the exposure and the outcome. **2. Why the Other Options are Incorrect:** * **Option B (Interviewer’s Bias):** This is a type of **Information/Measurement bias** where the investigator asks questions differently or probes more deeply with cases than with controls. * **Option C (Reduces bias):** Berksonian bias *introduces* systematic error; it does not reduce it. * **Option D (Systematic difference in characteristics):** While this is the general definition of **Selection Bias**, Berksonian bias is a *specific subtype* defined by the hospital admission mechanism. **3. High-Yield Clinical Pearls for NEET-PG:** * **Key Setting:** Always look for "Hospital-based study" in the question stem. * **Prevention:** The best way to avoid Berksonian bias is to select controls from the **community** rather than the hospital. * **Neyman Bias (Prevalence-Incidence Bias):** Often confused with Berksonian, this occurs when very severe or very mild cases are excluded (e.g., patients who die before reaching the hospital). * **Recall Bias:** Common in case-control studies where cases remember past exposures more vividly than controls.

Question 1

What is the measure of infectivity of a disease?

Accepted Answer

Secondary attack rate

Answer

Incidence rate

Answer

Prevalence rate

Answer

Case fatality rate

Question 2

Under the National Poliomyelitis Elimination Programme, how is poliomyelitis diagnosed?

Accepted Answer

Viral isolation in stool

Answer

Antibody titre rise in blood

Answer

Viral microscopy in stool

Answer

Clinical examination

Question 3

The high stationary stage of the demographic cycle is characterized by:

Accepted Answer

High birth rate, high death rate

Answer

High birth rate, low death rate

Answer

Low birth rate, high death rate

Answer

Low birth rate, low death rate

Question 4

Which cancer is best suited for screening procedures?

Accepted Answer

Colon cancer

Answer

Prostate cancer

Answer

Gastric cancer

Answer

None of the above

Question 5

What is Incidence Rate?

Accepted Answer

It represents the number of new cases in the community

Answer

It represents the number of old cases in the community

Answer

It represents the number of total cases in the community

Answer

It represents the number of cured cases in the community

Question 6

A survey was conducted on 7,000 drivers using mobile phones and found that 700 met with an accident. In the same period, out of 3,000 drivers not using mobile phones, 30 met with an accident. Calculate the relative risk?

Accepted Answer

10

Answer

5

Answer

3.99

Answer

8.339

Question 7

To test the association between a risk factor and a disease, which of the following represents the weakest study design?

Accepted Answer

Ecological study

Answer

Case-control study

Answer

Cohort study

Answer

Cross-sectional study

Question 8

Which of the following is NOT a strategy in preventing HIV transmission?

Accepted Answer

Anti-retroviral treatment

Answer

Education

Answer

Treatment of sexually transmitted diseases

Answer

Condoms

Question 9

Berkesonian bias refers to which of the following?

Accepted Answer

Different rates of admission to the hospital

Answer

Interviewer's bias

Answer

Reduces bias

Answer

Systematic difference in characteristics between cases and controls

Question 10

Which of the following is NOT included in Chapter XXI (Z00-Z99) of the ICD-10 classification?

Accepted Answer

Certain infectious and parasitic diseases

Answer

Factors influencing health status and contact with health services

Answer

Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified

Answer

External causes of morbidity

Epidemiology — MCQs

Epidemiology — MCQs

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