Epidemiology Practice Questions

Q: What is the purpose of double blinding in clinical trials?

To avoid both observer and subject bias. **Explanation** In clinical trials, **blinding** (or masking) is a fundamental epidemiological tool used to eliminate **bias**—the systematic error that can influence the results of a study. **Why Option D is Correct:** Double blinding is the gold standard in clinical trials where **neither the investigator (observer) nor the participant (subject)** knows which group (study or control) the subject has been assigned to. * **Avoiding Subject Bias:** If a patient knows they are receiving a new "miracle drug," they may report subjective improvement due to the placebo effect or psychological expectations. * **Avoiding Observer Bias:** If the researcher knows who is receiving the intervention, they may subconsciously measure outcomes more favorably or provide extra care to the study group, skewing the data. **Analysis of Incorrect Options:** * **Option A:** Comparability between groups is achieved through **Randomization**, not blinding. Randomization ensures that both known and unknown confounding factors are distributed equally. * **Option B & C:** These are components of double blinding, but individually they describe **Single Blinding** (where only the subject is unaware). Option D is the most comprehensive answer for "double" blinding. **High-Yield Clinical Pearls for NEET-PG:** * **Single Blind:** Only the subject is unaware. * **Double Blind:** Subject and Investigator are unaware. (Most common in RCTs). * **Triple Blind:** Subject, Investigator, and the **Data Analyst** (Statistician) are unaware. This is the most secure method to prevent bias. * **The "Placebo"** is the tool used to maintain blinding. * **Randomization** is the "Heart of a Control Trial"; it eliminates **Selection Bias**.

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 is NOT under international surveillance?

Yellow fever. To understand this question, it is essential to distinguish between the **International Health Regulations (IHR)** and the list of diseases under **International Surveillance**. ### **Why Yellow Fever is the Correct Answer** Yellow fever is categorized as a **Quarantinable Disease** (along with Plague and Cholera) under the International Health Regulations. These diseases require immediate notification to the WHO because they have the potential for rapid international spread. While they are monitored globally, they are technically classified under "International Health Regulations" rather than the specific list of "Diseases under International Surveillance." ### **Analysis of Incorrect Options** The WHO established a specific list of diseases under international surveillance to monitor their global trends, even if they don't always require immediate quarantine measures. * **A. Paralytic Polio:** Included in the surveillance list to monitor the progress of the Global Polio Eradication Initiative. * **C. Louse-borne Typhus Fever:** Included due to its potential for outbreaks in crowded, unsanitary conditions (e.g., refugee camps). * **D. Relapsing Fever:** Specifically the louse-borne variety, it is monitored internationally to prevent cross-border transmission. ### **High-Yield Clinical Pearls for NEET-PG** * **Diseases under International Surveillance (WHO):** Louse-borne typhus, Relapsing fever, Paralytic polio, Malaria, Viral influenza, and SARS. * **Quarantinable Diseases (IHR 1969):** Cholera, Plague, and Yellow Fever. * **IHR 2005 Update:** The focus shifted from specific diseases to "Public Health Emergencies of International Concern" (PHEIC). Under IHR 2005, any unusual or unexpected health event (including new strains of Flu or Ebola) must be reported. * **Yellow Fever Vaccination:** The certificate becomes valid **10 days** after vaccination and lasts for **life** (as per 2016 amendments).

Q: Secondary attack rate reflects the ------ of a disease?

Communicability. **Explanation:** **Secondary Attack Rate (SAR)** is defined as the number of exposed persons developing the disease within the range of the incubation period following exposure to a primary case. It is expressed as a percentage. 1. **Why Communicability is Correct:** SAR is the most sensitive indicator of **communicability** (infectiousness). It measures the spread of a disease from an infected person to susceptible contacts in a closed environment (like a household or dormitory). A high SAR indicates that the pathogen is highly contagious and spreads easily among contacts. 2. **Why Other Options are Incorrect:** * **Severity:** Refers to the degree of illness caused. It is often measured by the proportion of cases requiring hospitalization or resulting in disability. * **Fatality:** Measured by the **Case Fatality Rate (CFR)**, which represents the killing power of a disease (number of deaths among diagnosed cases). * **Virulence:** This is the ability of an infectious agent to cause severe disease or death. While related to severity, it is a property of the pathogen, whereas SAR is a measure of transmission dynamics. **High-Yield NEET-PG Pearls:** * **Formula:** $\text{SAR} = \frac{\text{Number of exposed persons developing disease within one incubation period}}{\text{Total number of susceptible contacts}} \times 100$. * **Denominator Rule:** In the denominator, "Total number of susceptible contacts" **excludes** the primary case and those already immune (e.g., through prior infection or vaccination). * **Application:** SAR is used to evaluate the effectiveness of control measures (like isolation or prophylactic antibiotics) and to identify the "hidden" spread of infection.

Q: A woman exposed to multiple sexual partners has a 5 times increased risk for Carcinoma Cervix. What is the attributable risk?

80%. ### Explanation **1. Understanding the Correct Answer (C: 80%)** The question provides the **Relative Risk (RR)**, which is 5. The **Attributable Risk (AR)**, also known as the Etiologic Fraction among the exposed, measures the proportion of the disease in the exposed group that can be specifically attributed to the risk factor. The formula for Attributable Risk (Percent) is: $$\text{AR\%} = \frac{RR - 1}{RR} \times 100$$ Plugging in the values: $$\text{AR\%} = \frac{5 - 1}{5} \times 100 = \frac{4}{5} \times 100 = 80\%$$ This means that 80% of cervical cancer cases among women with multiple sexual partners can be attributed to that specific behavior, and these cases could potentially be prevented if the risk factor were eliminated. **2. Why Other Options are Incorrect** * **A (20%):** This represents $1/RR$. It does not correspond to the attributable risk formula. * **B (50%):** This would be the result if the RR was 2. * **D (100%):** This would only occur if the risk factor was the *sole* cause of the disease (RR = infinity), which is rarely the case in multifactorial diseases. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Relative Risk (RR):** Measures the *strength* of association. It is best for identifying the etiology of a disease. * **Attributable Risk (AR):** Measures the *impact* of a risk factor. It indicates how much of the disease can be prevented by removing the exposure (Clinical/Public Health importance). * **Population Attributable Risk (PAR):** Estimates the benefit to the *entire population* (both exposed and non-exposed) if the risk factor is removed. * **Cervical Cancer:** The primary etiological agent is Human Papillomavirus (HPV) types 16 and 18. Multiple sexual partners increase the risk of HPV transmission.

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

What is the purpose of double blinding in clinical trials?

Accepted Answer

To avoid both observer and subject bias

Answer

To achieve comparability between study and control groups

Answer

To avoid observer bias

Answer

To avoid subject bias

Question 2

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

Accepted Answer

Disability

Answer

Impairment

Answer

Disease

Answer

Handicap

Question 3

Which of the following is true about secular trend?

Accepted Answer

Consistent change in a particular direction over a period of time.

Answer

A roadside accident is a good example.

Answer

Due to environmental factors.

Answer

Is due to normally occurring variation in herd immunity.

Question 4

Which of the following diseases is NOT under international surveillance?

Accepted Answer

Yellow fever

Answer

Paralytic polio

Answer

Louse-borne typhus fever

Answer

Relapsing fever

Question 5

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 6

Secondary attack rate reflects the ------ of a disease?

Accepted Answer

Communicability

Answer

Severity

Answer

Fatality

Answer

Virulence

Question 7

A woman exposed to multiple sexual partners has a 5 times increased risk for Carcinoma Cervix. What is the attributable risk?

Accepted Answer

80%

Answer

20%

Answer

50%

Answer

100%

Question 8

Which diseases are transmitted by the Culex mosquito?

Accepted Answer

Dengue

Answer

Malaria

Answer

Filariasis

Answer

Japanese encephalitis

Question 9

What is defined as a 'case' in Tuberculosis?

Accepted Answer

Sputum AFB positive

Answer

X-ray positive

Answer

Culture positive

Answer

Tuberculosis positive

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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