Epidemiology Practice Questions

Q: In an investigation to study the effect of smoking on renal cell carcinoma, it is observed that 30 out of 50 patients were smokers as compared to 10 out of 50 control subjects. What is the odd ratio of renal cell carcinoma associated with smoking?

6. ### Explanation **1. Understanding the Correct Answer (C: 6)** The study design described is a **Case-Control Study**, as it starts with known cases (Renal Cell Carcinoma) and compares them to controls to look back at an exposure (smoking). The appropriate measure of association for such studies is the **Odds Ratio (OR)**. To calculate the Odds Ratio, we use a 2x2 contingency table: | | Cases (RCC) | Controls | | :--- | :---: | :---: | | **Exposed (Smokers)** | 30 (a) | 10 (b) | | **Non-Exposed (Non-smokers)** | 20 (c) | 40 (d) | | **Total** | 50 | 50 | * **Formula:** $OR = \frac{ad}{bc}$ (Cross-product ratio) * **Calculation:** $OR = \frac{30 \times 40}{10 \times 20} = \frac{1200}{200} = 6$ * **Interpretation:** Smokers have 6 times higher odds of developing renal cell carcinoma compared to non-smokers. **2. Why Other Options are Incorrect** * **Option A (3):** This is a common error where students simply divide the number of exposed cases by exposed controls ($30/10$). This ignores the non-exposed group. * **Option B (0.33):** This is the inverse of 3 ($1/3$), often resulting from flipping the numerator and denominator. * **Option D (0.16):** This is the inverse of 6 ($1/6$), representing the odds of the control group rather than the cases. **3. High-Yield Clinical Pearls for NEET-PG** * **Odds Ratio (OR):** Used in Case-Control studies. It is an estimate of Relative Risk (RR). * **Relative Risk (RR):** Used in Cohort studies. It cannot be calculated in case-control studies because the incidence cannot be determined. * **Attributable Risk (AR):** Indicates the amount of disease that can be attributed to the exposure. * **Key Rule:** If OR > 1, the exposure is a risk factor. If OR = 1, there is no association. If OR < 1, the exposure is protective.

Q: Isolation is required to break the transmission of all the following diseases, except:

Tetanus. **Explanation:** The core concept behind **Isolation** is to separate infected persons (cases) from others during the period of communicability to prevent the direct or indirect transmission of an infectious agent. **1. Why Tetanus is the Correct Answer:** Tetanus is caused by the neurotoxin of *Clostridium tetani*. Crucially, tetanus is **not a communicable disease**; it is not transmitted from person to person. It is acquired through environmental exposure (e.g., soil-contaminated wounds). Since there is no risk of a patient spreading the infection to healthcare workers or other patients, isolation is medically unnecessary. **2. Why the other options are incorrect:** * **Swine Flu (Influenza A H1N1):** Highly contagious via respiratory droplets and aerosols. Isolation is mandatory to prevent hospital-acquired outbreaks. * **Mumps:** Transmitted via saliva and respiratory droplets. Patients are infectious from 3 days before to 9 days after the onset of parotid swelling, necessitating isolation. * **Measles:** One of the most highly communicable diseases (respiratory route). It requires strict isolation (preferably negative pressure rooms) due to its high secondary attack rate. **NEET-PG High-Yield Pearls:** * **Isolation vs. Quarantine:** Isolation applies to **sick individuals** (cases), while Quarantine applies to **healthy contacts** who were exposed. * **Non-communicable Infectious Diseases:** Tetanus is the classic example of an infectious but non-communicable disease. * **Duration of Isolation:** For most respiratory viral infections (like Measles/Mumps), isolation is required for the duration of the "Period of Communicability." * **Standard Precautions:** While Tetanus doesn't require isolation, standard wound-care precautions are always maintained.

Q: What is the first step in managing an epidemic?

Verification of diagnosis. ### Explanation In epidemiology, the management of an outbreak follows a systematic, step-by-step approach. The **first and most crucial step** is the **Verification of Diagnosis**. **1. Why "Verification of Diagnosis" is correct:** Before mobilizing resources or implementing control measures, it is essential to confirm that the reported cases are indeed the disease they are suspected to be. This prevents "false alarms" caused by misinterpretation of signs/symptoms or laboratory errors. Verification involves clinical examination of a sample of cases and confirming them through specific laboratory tests. Once the diagnosis is verified, the next step is to confirm the existence of an epidemic (comparing current incidence with previous years). **2. Why other options are incorrect:** * **Notification (D):** While notification to local health authorities is a legal requirement, it typically occurs *after* the diagnosis is verified and the existence of an epidemic is confirmed. * **Isolation (B):** This is a control measure. You cannot justify isolating individuals or restricting movement until you have confirmed what pathogen you are dealing with. * **Immunization (C):** This is a specific prevention strategy (if a vaccine is available). It is implemented much later in the investigation process as part of the "Control Measures" phase. **3. NEET-PG High-Yield Pearls:** * **Sequence of Investigation:** 1. Verification of diagnosis → 2. Confirmation of existence of epidemic → 3. Defining the population at risk → 4. Rapid search for all cases. * **Definition of Epidemic:** The occurrence of cases of an illness in a community or region clearly in excess of normal expectancy. * **Primary Case:** The first case of a disease to be introduced into a population. * **Index Case:** The first case that comes to the attention of the investigator (not necessarily the primary case).

Q: Subclinical infection is not seen in which of the following diseases?

Measles. **Explanation:** The concept of the **"Iceberg Phenomenon of Disease"** is central to understanding subclinical infections. In many diseases, the visible "tip" of the iceberg represents clinical cases, while the submerged portion represents subclinical, inapparent, or latent infections. **Why Measles is the Correct Answer:** Measles is a classic example of a disease that **does not show the iceberg phenomenon**. It is highly infectious and has a near-total clinical manifestation rate. Almost every individual infected with the measles virus will develop the characteristic clinical syndrome (fever, cough, coryza, conjunctivitis, and maculopapular rash). Therefore, subclinical cases are virtually non-existent in measles. **Analysis of Incorrect Options:** * **Mumps & Rubella:** Both are known to have a significant proportion of subclinical cases. In Rubella, up to 50% of infections can be asymptomatic, yet these individuals can still transmit the virus. * **Japanese Encephalitis (JE):** JE is a prime example of the iceberg phenomenon. The ratio of overt encephalitis to inapparent infection ranges from 1:300 to 1:1000. Most people infected with the JE virus remain asymptomatic. **High-Yield Clinical Pearls for NEET-PG:** * **Diseases NOT showing the Iceberg Phenomenon:** Measles, Rabies, and Tetanus (where every infection leads to clinical disease). * **Diseases showing the Iceberg Phenomenon:** Polio (classic example), Hepatitis A and B, JE, Mumps, Rubella, and Hypertension. * **Epidemiological Significance:** In diseases with an "iceberg," subclinical cases act as a hidden reservoir, making eradication more difficult compared to diseases like Measles.

Question 1

Which of the following statements regarding the Mantoux test is NOT true?

Accepted Answer

A positive test does not definitively mean the person has active TB disease.

Answer

The test is read before 48 hours.

Answer

6-9 mm induration suggests a high likelihood of developing TB.

Answer

New TB cases are less likely to occur in tuberculin-negative individuals compared to tuberculin reactors.

Question 2

Which of the following is FALSE regarding Randomised Control Trials?

Accepted Answer

Randomisation is done while selecting subjects for the study

Answer

Results of attrition are included in the analysis

Answer

Double blinding is the most common form of blinding observed

Answer

Cross-over design helps removing ethical concerns

Question 3

In an investigation to study the effect of smoking on renal cell carcinoma, it is observed that 30 out of 50 patients were smokers as compared to 10 out of 50 control subjects. What is the odd ratio of renal cell carcinoma associated with smoking?

Accepted Answer

6

Answer

3

Answer

0.33

Answer

0.16

Question 4

Isolation is required to break the transmission of all the following diseases, except:

Accepted Answer

Tetanus

Answer

Swine flu

Answer

Mumps

Answer

Measles

Question 5

In a randomized controlled trial, what is the essential purpose of randomization?

Accepted Answer

To eliminate selection bias

Answer

To produce double blinding

Answer

To decrease the follow-up period

Answer

To decrease the sample size

Question 6

What is the mode of transmission for a propagative epidemic?

Accepted Answer

Person to person

Answer

Animal to person

Answer

Water to person

Answer

Fomite to person

Question 7

What is the minimum density of microfilariae in blood required for a mosquito to become infected?

Accepted Answer

15 microfilariae per drop of blood

Answer

5 microfilariae per drop of blood

Answer

10 microfilariae per drop of blood

Answer

20 microfilariae per drop of blood

Question 8

What is the first step in managing an epidemic?

Accepted Answer

Verification of diagnosis

Answer

Isolation

Answer

Immunization

Answer

Notification

Question 9

In a population of 5000, 90 new cases of myopia were found over a year. Calculate the incidence of myopia per 100 people.

Accepted Answer

2

Answer

1.8

Answer

5

Answer

18

Question 10

Subclinical infection is not seen in which of the following diseases?

Accepted Answer

Measles

Answer

Mumps

Answer

Rubella

Answer

Japanese encephalitis

Epidemiology — MCQs

Epidemiology — MCQs

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