Epidemiology Practice Questions

Q: Which of the following diseases is NOT included in the National Vector Borne Disease Control Programme?

Yellow fever. The **National Vector Borne Disease Control Programme (NVBDCP)** is the central nodal agency in India for the prevention and control of six specific vector-borne diseases. ### **Why Yellow Fever is the Correct Answer** **Yellow Fever** is not included in the NVBDCP because it is **not endemic to India**. While the vector (*Aedes aegypti*) is present in the country, the virus itself is absent. India maintains strict International Health Regulations (IHR) regarding Yellow Fever vaccination for travelers to prevent its entry, but it is not part of the domestic control program. ### **Analysis of Incorrect Options** The NVBDCP currently covers **six** diseases. The three listed in the options are integral parts of the program: * **Malaria (Option A):** One of the primary focuses, with a goal of elimination by 2030. * **Japanese Encephalitis (Option C):** A major cause of viral encephalitis in India, particularly in the "JE belt" (UP, Bihar, West Bengal). * **Kala-azar (Option D):** Also known as Visceral Leishmaniasis, transmitted by the sandfly (*Phlebotomus argentipes*), targeted for elimination in endemic states. ### **High-Yield Clinical Pearls for NEET-PG** * **The Six Diseases under NVBDCP:** Malaria, Dengue, Chikungunya, Japanese Encephalitis, Kala-azar, and Lymphatic Filariasis. * **Elimination Targets:** India aims to eliminate **Kala-azar** and **Lymphatic Filariasis** (defined as <1 case per 10,000 population at the block/district level). * **Vector Fact:** *Aedes aegypti* is the common vector for Dengue, Chikungunya, and Yellow Fever. * **Administrative Note:** NVBDCP has now been subsumed under the **National Center for Vector Borne Diseases Control (NCVBDC)** under the National Health Mission.

Q: Subclinical infection is seen in all except?

Measles. **Explanation:** The concept of **Subclinical Infection** refers to an infection where the pathogen multiplies in the host but does not manifest any recognizable clinical signs or symptoms. In epidemiology, this is often represented by the **"Iceberg Phenomenon of Disease,"** where subclinical cases form the submerged portion of the iceberg. **Why Measles is the correct answer:** Measles is a classic example of a disease that **does not** have a subclinical state. It is highly infectious and characterized by a near-100% clinical attack rate in susceptible individuals. Almost every person infected with the Measles virus will manifest the typical clinical syndrome (fever, cough, coryza, conjunctivitis, and the pathognomonic Koplik’s spots followed by a rash). Therefore, it does not contribute to the "submerged" portion of the iceberg. **Analysis of Incorrect Options:** * **Poliomyelitis:** This is the quintessential example of the Iceberg Phenomenon. Over 90-95% of cases are asymptomatic (subclinical), while paralytic polio represents only the "tip." * **Rubella:** Frequently presents as a mild or subclinical infection, especially in children. Subclinical cases are significant as they can still lead to Congenital Rubella Syndrome (CRS) if a pregnant woman is exposed. * **Mumps:** Approximately 30-40% of Mumps infections are subclinical or asymptomatic but can still spread the virus to others. **High-Yield Clinical Pearls for NEET-PG:** * **Iceberg Phenomenon NOT seen in:** Measles, Rabies, and Tetanus (these diseases are almost always clinically apparent). * **Iceberg Phenomenon SEEN in:** Polio, Hypertension, Diabetes, Malnutrition, and Japanese Encephalitis. * **Tip of the Iceberg:** Represents what the physician sees (clinical cases). * **Submerged portion:** Represents the burden for the Epidemiologist (subclinical, carriers, and undiagnosed cases).

Q: What is the advantage of a cohort study?

More than one outcome can be studied. ### Explanation **Why the correct answer is right:** A **Cohort Study** is a longitudinal, prospective observational study that starts with a group of individuals (the cohort) who are free of the disease but classified based on their exposure status. Because the study follows these individuals forward in time from **exposure to outcome**, researchers can observe the development of various different conditions. For example, in a cohort study of smokers, one can simultaneously study the incidence of lung cancer, coronary heart disease, and COPD. This ability to link a single exposure to **multiple outcomes** is a hallmark advantage. **Why the incorrect options are wrong:** * **A & B (Small number of subjects / Inexpensive):** Cohort studies typically require a **large sample size** and long follow-up periods to ensure enough cases of the disease occur. This makes them significantly more **expensive** and time-consuming compared to case-control studies. * **C (Suitable for rare diseases):** Cohort studies are **inefficient for rare diseases** because one would have to follow a massive number of people for a very long time to see even a few cases. **Case-control studies** are the design of choice for rare diseases. **High-Yield Pearls for NEET-PG:** * **Best for Rare Exposures:** Cohort studies are the gold standard for studying rare exposures (e.g., occupational chemical leaks). * **Incidence & Risk:** Cohort studies are the only observational study design that can directly calculate **Incidence**, **Relative Risk (RR)**, and **Attributable Risk (AR)**. * **Temporal Association:** They provide the strongest evidence of causality among observational studies because they establish that the exposure clearly preceded the outcome. * **Selection Bias:** Cohort studies are prone to **"Loss to follow-up"** (attrition bias).

Q: Which of the following diseases does NOT have healthy carriers?

Typhoid. **Explanation:** The correct answer is **Typhoid (A)**. This question hinges on the distinction between different types of carriers in epidemiology. A **healthy carrier** is an individual who harbors the pathogen but has never suffered from the clinical disease (subclinical infection). In **Typhoid fever**, carriers are almost exclusively **convalescent carriers** (those who shed bacilli during or after recovery) or **chronic carriers** (those who shed bacilli for more than a year, often due to colonization of the gallbladder). A person does not typically become a typhoid carrier without first undergoing the clinical or subclinical stages of the disease. **Analysis of Incorrect Options:** * **Cholera (B):** Known for having a high ratio of healthy (subclinical) carriers to clinical cases. These carriers play a major role in the environmental spread of *Vibrio cholerae*. * **Diphtheria (C):** Healthy carriers are common in the community and are often more important than clinical cases in maintaining the reservoir of *Corynebacterium diphtheriae* in the nasopharynx. * **Tuberculosis (D):** The majority of individuals infected with *Mycobacterium tuberculosis* have "Latent TB Infection." These are essentially healthy carriers who harbor the dormant bacilli without active clinical disease. **NEET-PG High-Yield Pearls:** * **Typhoid:** The "Chronic Carrier" state is most common in females and is associated with gallstones (Gallbladder is the reservoir). **Mary Mallon ("Typhoid Mary")** is the classic historical example. * **Incubatory Carrier:** Sheds infectious agent during the incubation period (e.g., Measles, Mumps, Hepatitis B). * **Convalescent Carrier:** Sheds infectious agent during the period of recovery (e.g., Typhoid, Dysentery). * **Pseudo-carrier:** A term sometimes used for those carrying non-pathogenic strains (not a standard epidemiological term).

Q: Which of the following study designs is considered non-biased?

Randomized controlled trial. **Explanation:** The core concept behind a **Randomized Controlled Trial (RCT)** being "non-biased" lies in the process of **Randomization**. Randomization is often called the "heart" of an RCT because it ensures that every participant has an equal chance of being assigned to either the study or control group. This process eliminates **Selection Bias** and, more importantly, ensures that both known and unknown **confounding factors** are distributed equally between the groups. This makes the groups comparable, allowing any difference in outcome to be attributed solely to the intervention. **Analysis of Incorrect Options:** * **Case-Control Study:** These are retrospective and highly prone to **Recall Bias** (patients forgetting past exposures) and **Selection Bias**, as participants are selected based on the outcome. * **Cohort Study:** While prospective, these are observational. Since researchers do not assign the exposure, **Selection Bias** and **Confounding** are major issues (e.g., smokers might have different lifestyles than non-smokers). * **Unrandomized Trial:** Without randomization, the investigator may consciously or unconsciously assign "healthier" patients to the treatment group, leading to significant **Allocation Bias**. **NEET-PG High-Yield Pearls:** * **Gold Standard:** RCT is the gold standard for evaluating the efficacy of a new drug or therapeutic procedure. * **Randomization vs. Blinding:** Remember, Randomization eliminates **Selection Bias/Confounding**, while Blinding eliminates **Observer/Information Bias**. * **Confounding:** RCT is the only study design that can control for *unknown* confounders. * **Hierarchy of Evidence:** Meta-analysis of RCTs > Individual RCT > Cohort > Case-Control > Case Series.

Question 1

Which of the following diseases is NOT included in the National Vector Borne Disease Control Programme?

Accepted Answer

Yellow fever

Answer

Malaria

Answer

Japanese encephalitis

Answer

Kala azar

Question 2

Primary prevention includes all, except:

Accepted Answer

Self breast examination

Answer

Marriage counselling

Answer

Health education

Answer

Health promotion

Question 3

An epidemiologic study observes increased numbers of respiratory tract infections among children living in a community in which most families are at the poverty level. The infectious agents include Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneumoniae. Most of the children have had pneumonitis and rubeola infection. The study documents increased rates of keratomalacia, urinary tract calculi, and generalized papular dermatosis in these children as they reach adulthood. These children are most likely to have a deficiency of which of the following vitamins?

Accepted Answer

Vitamin A

Answer

Vitamin B1

Answer

Vitamin E

Answer

Vitamin D

Question 4

Subclinical infection is seen in all except?

Accepted Answer

Measles

Answer

Mumps

Answer

Poliomyelitis

Answer

Rubella

Question 5

What is the advantage of a cohort study?

Accepted Answer

More than one outcome can be studied

Answer

Involves a smaller number of subjects

Answer

Inexpensive

Answer

Suitable for rare diseases

Question 6

True morbidity in a population can be calculated by which of the following methods?

Accepted Answer

Active Surveillance

Answer

Sentinel Surveillance

Answer

Passive Surveillance

Answer

Monitoring

Question 7

What are the criteria for the validity of a screening test?

Accepted Answer

Predictability

Answer

Accuracy

Answer

Sensitivity and Specificity

Answer

Cost-effectiveness

Question 8

Which of the following diseases does NOT have healthy carriers?

Accepted Answer

Typhoid

Answer

Cholera

Answer

Diphtheria

Answer

Tuberculosis

Question 9

Which of the following study designs is considered non-biased?

Accepted Answer

Randomized controlled trial

Answer

Case control study

Answer

Cohort study

Answer

Unrandomized trial

Question 10

Which of the following is NOT indicated by the Hardy-Weinberg law?

Accepted Answer

Natural selection is a process where harmful genes are eliminated from the gene pool and genes favorable to the individual are passed on to offspring.

Answer

Genotype frequencies in a population remain constant from generation to generation unless specific disturbing influences are introduced.

Answer

A population is static.

Answer

Factors influencing the gene pool include mutation, natural selection, population movements (assortive mating), and public health measures.

Epidemiology — MCQs

Epidemiology — MCQs

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