Epidemiology Practice Questions

Q: What measure is estimated in a case-control study?

Odds ratio. ### Explanation In epidemiology, the choice of study design dictates which measures of association can be calculated. **Why Option A is Correct:** A **Case-Control Study** is retrospective; it starts with the outcome (disease) and looks backward to determine exposure. Because the researcher determines the number of cases and controls, the true **Incidence** of the disease cannot be calculated. Without incidence, we cannot calculate Relative Risk (RR). Instead, we use the **Odds Ratio (OR)**, which estimates the strength of the association between exposure and outcome by comparing the odds of exposure among cases to the odds of exposure among controls. **Why Other Options are Incorrect:** * **Options C and D:** These include **Incidence, Relative Risk (RR), and Attributable Risk (AR)**. These measures require the calculation of incidence (new cases over time), which can only be directly measured in a **Cohort Study** (prospective design). * **Option B:** While it includes Odds Ratio, it also includes Attributable Risk. Attributable Risk requires incidence data from a cohort to determine how much of the disease is specifically due to the exposure. **High-Yield Clinical Pearls for NEET-PG:** * **Case-Control Study:** Best for **rare diseases** or diseases with long latency periods. It is fast and inexpensive but prone to **recall bias**. * **Cohort Study:** Best for **rare exposures**. It can calculate Incidence, RR, AR, and PAR. * **Odds Ratio vs. Relative Risk:** OR is a good estimate of RR when the disease is rare (the "Rare Disease Assumption"). * **Formula for OR:** $(a/c) / (b/d)$ or simply $ad/bc$ (cross-product ratio).

Q: Which of the following is a live attenuated vaccine?

Measles. **Explanation:** Live attenuated vaccines are prepared from wild viruses or bacteria that have been weakened (attenuated) in a laboratory. They replicate in the recipient to produce an immune response without causing the actual disease. 1. **Correct Answer: Measles (Option A):** The Measles vaccine (Edmonston-Zagreb strain) is a classic example of a live attenuated viral vaccine. It is typically administered at 9 months and 16–24 months under the Universal Immunization Programme (UIP). 2. **Incorrect Options:** * **Rabies (Option B):** This is a **killed/inactivated vaccine**. In India, the most common type is the Human Diploid Cell Vaccine (HDCV) or Purified Chick Embryo Cell Vaccine (PCECV). * **Hepatitis B (Option C):** This is a **recombinant/subunit vaccine** produced using yeast cells (*Saccharomyces cerevisiae*) containing the HBsAg gene. * **Typhoid (Option D):** While a live oral typhoid vaccine (Ty21a) exists, the standard injectable typhoid vaccine used in many programs is the **Vi polysaccharide** or **Typhoid Conjugate Vaccine (TCV)**, which are inactivated. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Live Vaccines:** "**BOY** **R**omeo **M**eets **V**ictoria **L**ately **I**n **T**hailand" (**B**CG, **O**PV, **Y**ellow Fever, **R**otavirus, **M**easles/MMR, **V**aricella, **L**ive **I**nfluenza, **T**yphoid Ty21a). * **Contraindication:** Live vaccines are generally contraindicated in pregnancy and immunocompromised states (except HIV patients before the symptomatic stage). * **Storage:** Most live vaccines are highly heat-sensitive and must be stored in the freezer compartment or at +2°C to +8°C.

Q: In which one of the following does the host factor show a bimodal incidence curve?

Hodgkin's lymphoma. **Explanation:** The correct answer is **Hodgkin’s Lymphoma (HL)**. In epidemiology, a **bimodal incidence curve** refers to a distribution where there are two distinct peaks of occurrence across different age groups. 1. **Why Hodgkin’s Lymphoma is correct:** HL classically exhibits two peaks in developed countries: * **First Peak:** Young adults (typically aged 15–34 years). * **Second Peak:** Older adults (typically aged 50 years and above). This pattern is thought to reflect different etiologies, such as a possible infectious trigger (like EBV) in younger patients versus age-related immune senescence or different genetic factors in the elderly. 2. **Analysis of Incorrect Options:** * **Kaposi’s Sarcoma:** Generally shows a linear or unimodal increase in incidence, particularly associated with HIV/AIDS status or elderly Mediterranean men, but does not follow a classic bimodal age distribution. * **Osteosarcoma:** While it has a major peak during the adolescent growth spurt, the secondary rise in the elderly (often associated with Paget’s disease) is less pronounced and not considered a classic "bimodal curve" in the same epidemiological context as HL. * **Lung Cancer:** Shows a **unimodal** distribution where the incidence increases steadily with age, peaking in the 6th or 7th decade of life, primarily due to cumulative exposure to carcinogens like tobacco smoke. **High-Yield Clinical Pearls for NEET-PG:** * **Other Bimodal Diseases:** Apart from HL, **Systemic Lupus Erythematosus (SLE)** and **Ulcerative Colitis** are often cited as having bimodal age distributions. * **HL Histology:** The presence of **Reed-Sternberg (RS) cells** ("Owl-eye appearance") is the pathognomonic feature. * **EBV Association:** The Mixed Cellularity subtype of HL has the strongest association with the Epstein-Barr Virus.

Q: The Aedes aegypti index should be less than what percentage?

1%. **Explanation:** The **Aedes aegypti index** (also known as the House Index) is a key entomological indicator used to monitor the risk of transmission for diseases like Dengue, Chikungunya, and Zika. It is defined as the percentage of houses found positive for Aedes aegypti larvae or pupae. **1. Why 1% is the correct answer:** According to World Health Organization (WHO) and National Vector Borne Disease Control Programme (NVBDCP) guidelines, an Aedes aegypti index of **less than 1%** is considered the "safety threshold." When the index is maintained below 1%, the risk of an epidemic outbreak is considered negligible. If the index rises above this level, it indicates a potential for disease transmission. **2. Analysis of Incorrect Options:** * **B (5%):** While a 5% threshold is sometimes used for the *Breteau Index* (number of positive containers per 100 houses) to indicate low risk, it is not the safety standard for the House Index. * **C & D (8% and 10%):** These values represent high-risk scenarios. An index exceeding 10% is often associated with a high probability of an explosive outbreak during the transmission season. **3. NEET-PG High-Yield Pearls:** * **House Index (HI):** (Houses positive / Houses inspected) × 100. * **Container Index (CI):** (Containers positive / Containers inspected) × 100. * **Breteau Index (BI):** (Number of positive containers / Total houses inspected) × 100. (Considered the best predictor of Aedes density). * **Aedes aegypti** is a "day biter," breeds in clean stagnant water (artificial containers), and exhibits "intermittent feeding" (biting multiple people to complete one blood meal), which increases its epidemic potential.

Q: The mass treatment of trachoma is undertaken if the prevalence in the community is:

5%. **Explanation:** The correct answer is **5%**. This threshold is based on the **WHO SAFE Strategy** for the elimination of blinding trachoma. **1. Why 5% is Correct:** According to WHO guidelines, mass drug administration (MDA) with antibiotics (usually oral Azithromycin) is indicated when the prevalence of **Trachomatous Inflammation—Follicular (TF)** in children aged 1–9 years is **5% or higher**. * If prevalence is **≥5%**, annual mass treatment is required for at least 3 years before re-surveying. * The goal is to reduce the community reservoir of *Chlamydia trachomatis* to levels where transmission is no longer sustainable. **2. Why Other Options are Incorrect:** * **3% (Option A):** This is below the intervention threshold. At this level, the disease is monitored, but mass treatment is not considered cost-effective or epidemiologically necessary. * **10% (Option D):** Previously, 10% was a significant benchmark for more intensive annual treatment. However, the current WHO recommendation for initiating MDA starts at the lower threshold of **5%** to ensure elimination. * **6% (Option D):** While 6% would technically trigger mass treatment (as it is >5%), it is not the standard "cutoff" value defined in public health guidelines. **3. High-Yield Clinical Pearls for NEET-PG:** * **SAFE Strategy:** **S**urgery (for trichiasis), **A**ntibiotics (MDA), **F**acial cleanliness, **E**nvironmental improvement. * **Drug of Choice:** A single dose of **Azithromycin (20 mg/kg)** is the mainstay of mass treatment. Tetracycline eye ointment (1%) is an alternative. * **Target Population:** For MDA, the prevalence is specifically measured in children aged **1–9 years**, as they are the primary reservoir of infection. * **Elimination Goal:** India has been declared free from "infective trachoma," but surveillance continues to prevent recurrence.

Question 1

Which of the following statements is true regarding the Maternal Mortality Rate (MMR)?

Accepted Answer

The numerator includes deaths related to pregnancy complications up to 42 days after pregnancy ends.

Answer

MMR is calculated as a ratio.

Answer

The denominator includes stillbirths and abortions.

Answer

MMR is expressed as a rate per 1000 live births.

Question 2

Which of the following are used to evaluate a screening test?

Accepted Answer

All the above

Answer

Sensitivity

Answer

Specificity

Answer

Predictive value

Question 3

What is the term for the presence of a causative agent without transmission?

Accepted Answer

Elimination

Answer

Control

Answer

Eradication

Answer

Holoendemic

Question 4

What measure is estimated in a case-control study?

Accepted Answer

Odds ratio

Answer

Odds ratio and attributable risk

Answer

Relative risk, attributable risk, population attributable risk

Answer

Incidence, Relative risk, and attributable risk

Question 5

Which of the following best defines a pandemic?

Accepted Answer

An epidemic that has spread over several countries or continents, affecting a large number of people.

Answer

An epidemic confined to a small population.

Answer

A disease that is constantly present in a large population.

Answer

An epidemic that has spread to a small region.

Question 6

Which of the following is a live attenuated vaccine?

Accepted Answer

Measles

Answer

Rabies

Answer

Hepatitis B

Answer

Typhoid

Question 7

In which one of the following does the host factor show a bimodal incidence curve?

Accepted Answer

Hodgkin's lymphoma

Answer

Kaposi's Sarcoma

Answer

Osteosarcoma

Answer

Lung cancer

Question 8

The Aedes aegypti index should be less than what percentage?

Accepted Answer

1%

Answer

5%

Answer

8%

Answer

10%

Question 9

The mass treatment of trachoma is undertaken if the prevalence in the community is:

Accepted Answer

5%

Answer

3%

Answer

10%

Answer

6%

Question 10

Which of the following does not determine specific protection?

Accepted Answer

Pap smear for early detection of carcinoma cervix in the community

Answer

Wearing of goggles by welders

Answer

Wearing of seat belts by car drivers

Answer

Vitamin A supplementation for children's prophylaxis

Epidemiology — MCQs

Epidemiology — MCQs

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