Epidemiology Practice Questions

Q: Subclinical cases are seen in all of the following infections except?

Measles. ### Explanation The concept of **Subclinical Cases** refers to individuals who are infected with a pathogen but do not manifest any clinical signs or symptoms. These individuals are often referred to as "inapparent" or "asymptomatic" cases and play a significant role in the transmission of many diseases. **Why Measles is the Correct Answer:** Measles is characterized by a **high degree of pathogenicity**, meaning almost every susceptible individual who becomes infected will develop clinical symptoms (fever, cough, coryza, and the characteristic maculopapular rash). In Measles, subclinical cases are virtually non-existent; it follows an "all-or-none" phenomenon. This makes Measles an ideal candidate for eradication, as there is no hidden reservoir of asymptomatic carriers. **Analysis of Incorrect Options:** * **Rubella:** Unlike Measles, Rubella is notorious for subclinical infections. Up to 50% of cases can be asymptomatic, which is why it spreads easily in communities and poses a risk to pregnant women (Congenital Rubella Syndrome). * **Polio:** Polio is the classic example of the **"Iceberg Phenomenon."** Over 90–95% of infections are subclinical or inapparent, while only a small fraction results in paralytic disease. * **Influenza:** Influenza viruses frequently cause subclinical or mild infections that do not meet the full clinical criteria for "flu," allowing for rapid community spread. **High-Yield Clinical Pearls for NEET-PG:** 1. **Iceberg Phenomenon:** Diseases like Polio, Rubella, and Hepatitis A show this (where the "tip" is the clinical case and the "submerged portion" is the subclinical case). 2. **Diseases NOT showing Iceberg Phenomenon:** Measles, Rabies, and Tetanus (clinical disease is almost always apparent). 3. **Secondary Attack Rate (SAR):** Measles has one of the highest SARs (>80%), reflecting its extreme infectivity among susceptibles.

Q: Which of the following vaccines is NOT a freeze-dried vaccine?

DPT. **Explanation:** The core concept tested here is the **thermostability** of vaccines and their storage requirements. Vaccines are categorized based on their sensitivity to heat or cold. **Why DPT is the correct answer:** DPT (Diphtheria, Pertussis, and Tetanus) is a **liquid vaccine** and is never freeze-dried. It is highly **freeze-sensitive**. If DPT is frozen, the aluminum adjuvant precipitates, leading to a loss of potency and an increased risk of sterile abscesses at the injection site. Therefore, it must be stored in the "cold part" of the refrigerator (2°C to 8°C) but never in the freezer. **Why the other options are incorrect:** * **BCG:** This is a live attenuated, **freeze-dried (lyophilized)** vaccine. It is highly heat-sensitive in its reconstituted form but stable when dry. * **Measles:** This is a live attenuated **freeze-dried** vaccine. It is extremely heat-sensitive and must be protected from light. * **Yellow Fever:** This is a live attenuated **freeze-dried** vaccine (17D strain). It is one of the most heat-sensitive vaccines in the immunization program. **High-Yield NEET-PG Pearls:** 1. **Freeze-Dried Vaccines:** BCG, Measles/MR/MMR, Yellow Fever, JE (Live), and Varicella. 2. **Freeze-Sensitive Vaccines (The "T" Series):** DPT, TT, DT, Hepatitis B, and Pentavalent. These must **never** be frozen. 3. **The Shake Test:** Used to check if a freeze-sensitive vaccine (like DPT) has been damaged by sub-zero temperatures. 4. **Most Heat-Sensitive Vaccine:** Oral Polio Vaccine (OPV). 5. **Most Heat-Resistant Vaccine:** Tetanus Toxoid (TT).

Q: What is the incubation period of the Shope papilloma virus infection?

Influenza. **Explanation:** The question asks for a comparison of incubation periods (IP) between the **Shope papilloma virus** and common viral infections. The Shope papilloma virus (a cottontail rabbit papillomavirus) is historically significant in virology as one of the first models for virus-induced cancer. In experimental settings, it has an exceptionally short incubation period, often manifesting in as little as **1 to 5 days**. **Why Influenza is the Correct Answer:** Among the options provided, **Influenza** has the shortest incubation period, typically ranging from **1 to 3 days**. In epidemiological comparisons, the Shope papilloma virus is often grouped with Influenza because both represent the "short" end of the IP spectrum (usually less than 3–5 days). **Analysis of Incorrect Options:** * **Chickenpox (Varicella):** Has a long incubation period, typically **14 to 16 days** (range 10–21 days). * **Measles (Rubeola):** Has an incubation period of approximately **10 days** to the onset of fever and **14 days** to the appearance of the rash. * **Rubella (German Measles):** Has a long incubation period, usually **14 to 21 days** (average 18 days). **NEET-PG High-Yield Pearls:** * **Shortest IP:** Influenza (1–3 days), Cholera (1–5 days), Bacterial food poisoning (hours). * **Longest IP:** Leprosy (3–5 years), HIV (months to years), Hepatitis B (45–180 days). * **Median IP:** This is the most useful measure for epidemiologists to determine the time of exposure during an outbreak. * **Quarantine Period:** Usually corresponds to the **maximum** incubation period of a disease.

Q: Which of the following is NOT true of the attack rate?

It is a type of prevalence rate.. **Explanation** **1. Why Option A is the correct answer (Why it is NOT true):** The attack rate is actually a type of **Incidence Rate**, not a prevalence rate. Incidence measures the number of *new cases* occurring in a susceptible population over a specific period. Since an attack rate tracks new cases during an outbreak, it is technically a "cumulative incidence" used when the period of observation is short (e.g., a food poisoning outbreak). Prevalence, conversely, includes both old and new cases at a specific point in time. **2. Analysis of Incorrect Options (Why they are true of Attack Rate):** * **Option B:** Unlike the standard incidence rate (usually per 1,000), the attack rate is almost always expressed as a **percentage** (Number of new cases / Total population at risk × 100). * **Option C:** It is specifically designed for situations where a population is exposed to a risk for a **limited/short period**, such as an epidemic or a localized outbreak. * **Option D:** It is a primary tool to measure the **extent and severity** of an epidemic, helping epidemiologists identify the source and the speed of spread. **3. High-Yield Clinical Pearls for NEET-PG:** * **Secondary Attack Rate (SAR):** Measures the spread of a disease from a primary case to contacts within a closed group (e.g., household). It is the best indicator of **communicability/infectivity**. * **Formula for SAR:** (Number of exposed persons developing the disease within the incubation period / Total number of susceptible contacts) × 100. (Note: The primary case is excluded from both the numerator and denominator). * **Denominator:** Always remember that the denominator for an attack rate must only include those **at risk** (susceptible individuals).

Q: In a given population, how can the prevalence of a disease be rapidly determined?

Cross sectional study. ### Explanation **Why Cross-sectional Study is Correct:** A **Cross-sectional study** (also known as a Prevalence Study) is the method of choice for determining the prevalence of a disease. It examines a population at a **single point in time** (a "snapshot"), measuring both the exposure and the outcome simultaneously. Because it captures all existing cases (both old and new) at that specific moment, it directly calculates prevalence (Prevalence = Incidence × Average Duration). It is considered "rapid" because there is no follow-up period required. **Why the Other Options are Incorrect:** * **Case-control study:** This is a retrospective study that starts with the outcome (cases) and looks back for exposure. It is used to calculate **Odds Ratio**, not prevalence. * **Cross-over study:** This is a type of interventional trial where participants receive a sequence of different treatments. It is used to compare the efficacy of drugs, not to measure disease frequency in a population. * **Double-blind study:** This refers to a technique used in Randomized Controlled Trials (RCTs) to eliminate observer and participant bias. It is a method of study design/blinding, not a tool for measuring prevalence. **NEET-PG High-Yield Pearls:** * **Snapshot Study:** Another name for Cross-sectional study. * **Sequence:** In cross-sectional studies, the temporal association cannot be established (you don't know if the exposure preceded the disease). * **Formula:** Prevalence = Incidence × Duration ($P = I \times D$). If a disease is chronic (long duration), prevalence will be high even if incidence is low. * **Best for:** Chronic diseases and generating hypotheses. For rare diseases, Case-control studies are preferred.

Q: Which statistical test is used to compare quantitative data from the same group of individuals before and after an intervention or study?

Paired t-test. ### Explanation **1. Why Paired t-test is correct:** The **Paired t-test** (also known as the dependent t-test) is used to compare the means of two related groups. In medical research, this typically involves a **"Before and After"** study design where measurements are taken from the same set of individuals (e.g., measuring blood pressure before and after starting an antihypertensive drug). Since the data points are linked to the same subject, they are not independent, necessitating a paired analysis to account for individual baseline variations. **2. Why other options are incorrect:** * **Unpaired t-test (Independent t-test):** Used to compare the means of two **independent** groups (e.g., comparing the hemoglobin levels of Group A vs. Group B). * **Z-test:** Used for comparing means when the **sample size is large (n > 30)** and the population variance is known. While it can be paired or unpaired, the t-test is the standard choice for clinical trials with smaller samples. * **Chi-square test:** Used for **qualitative (categorical) data** (e.g., comparing the proportion of smokers vs. non-smokers in two groups). It is not used for quantitative data like blood sugar or weight. **3. NEET-PG High-Yield Clinical Pearls:** * **Quantitative Data (Means):** Think T-test (2 groups) or ANOVA (>2 groups). * **Qualitative Data (Proportions):** Think Chi-square or Fischer’s Exact test. * **Non-Parametric Equivalent:** If the data is not normally distributed, the non-parametric alternative to the Paired t-test is the **Wilcoxon Signed-Rank Test**. * **Memory Aid:** **P**aired = **P**re and **P**ost intervention in the same person.

Q: Vaccines at a Primary Health Centre (PHC) are stored in which of the following?

Ice-lined refrigerator (ILR). **Explanation:** The **Ice-lined Refrigerator (ILR)** is the backbone of the cold chain at the Primary Health Centre (PHC) level. It is specifically designed to maintain a stable temperature between **+2°C to +8°C**, which is the ideal range for storing most vaccines, including heat-sensitive ones like BCG and Measles, and frost-sensitive ones like DPT and Hepatitis B. The "ice-lining" (tubes or panels filled with water) ensures that even during a power failure of up to 24 hours, the internal temperature remains within the safe range. **Analysis of Options:** * **Ice-lined Refrigerator (ILR):** Correct. It is the primary storage equipment at PHCs and District levels for keeping vaccines at the required +2°C to +8°C. * **Deep Freezer:** Incorrect. At the PHC level, deep freezers are primarily used for **preparing ice packs** and storing OPV (if required). Storing frost-sensitive vaccines (Tseries) here would lead to loss of potency. * **Ice Box:** Incorrect. These are used for the **transportation** of vaccines from the PHC to outreach sessions (sub-centers/villages) or during short-term emergencies, but not for long-term storage at the facility. **High-Yield Clinical Pearls for NEET-PG:** * **Cold Chain Levels:** Regional/District levels use Walk-in-Coolers (WIC); PHCs use ILRs; Sub-centers use Vaccine Carriers. * **Placement in ILR:** Heat-sensitive vaccines (OPV, Measles) are kept at the bottom (coolest part), while freeze-sensitive vaccines (TT, DPT, Hep B) are kept at the top to prevent freezing. * **Monitoring:** Temperature should be recorded **twice daily**. * **Shake Test:** Used to determine if a freeze-sensitive vaccine (like DPT) has been damaged by sub-zero temperatures.

Question 1

Sullivan index is an index for what?

Accepted Answer

Life free of disability

Answer

Life Expectancy

Answer

Earning capacity

Answer

Population index

Question 2

Subclinical cases are seen in all of the following infections except?

Accepted Answer

Measles

Answer

Rubella

Answer

Polio

Answer

Influenza

Question 3

Which of the following conditions does NOT present with a latent infection?

Accepted Answer

Mumps

Answer

Herpes simplex

Answer

Brill-Zinsser disease

Answer

Ancylostomiasis

Question 4

Which of the following vaccines is NOT a freeze-dried vaccine?

Accepted Answer

DPT

Answer

BCG

Answer

Measles

Answer

Yellow fever

Question 5

After administration of a live vaccine, immunoglobulins should be given after how many weeks?

Accepted Answer

2 weeks

Answer

1 week

Answer

10 weeks

Answer

12 weeks

Question 6

What is the incubation period of the Shope papilloma virus infection?

Accepted Answer

Influenza

Answer

Chickenpox

Answer

Measles

Answer

Rubella

Question 7

Which of the following is NOT true of the attack rate?

Accepted Answer

It is a type of prevalence rate.

Answer

It is expressed as a percentage.

Answer

It is used when the population is exposed to a risk for a limited period of time.

Answer

It reflects the extent of an epidemic.

Question 8

In a given population, how can the prevalence of a disease be rapidly determined?

Accepted Answer

Cross sectional study

Answer

Case control study

Answer

Cross over study

Answer

Double blind study

Question 9

Which statistical test is used to compare quantitative data from the same group of individuals before and after an intervention or study?

Accepted Answer

Paired t-test

Answer

Unpaired t-test

Answer

Z-test

Answer

Chi-square test

Question 10

Vaccines at a Primary Health Centre (PHC) are stored in which of the following?

Accepted Answer

Ice-lined refrigerator (ILR)

Answer

Ice box

Answer

Deep freezer

Answer

None of the above

Epidemiology — MCQs

Epidemiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?