Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 301: Which vaccine is contraindicated in pregnancy?

A. Tuberculin (Correct Answer)
B. Typhoid
C. Influenza
D. HBV

Explanation: **Explanation:** The correct answer is **A. Tuberculin**. **Why Tuberculin is the correct choice:** Strictly speaking, Tuberculin (PPD) is a diagnostic antigen used for the Mantoux test, not a vaccine. However, in the context of this question, it is the only option that is generally **avoided** during pregnancy. While there is no evidence that the Tuberculin Skin Test (TST) is teratogenic, clinical guidelines (including those from the WHO and various national health bodies) suggest deferring elective skin testing until after delivery unless the woman is at high risk for active tuberculosis. This is primarily to avoid diagnostic confusion and potential hypersensitivity reactions during the altered immunological state of pregnancy. **Analysis of Incorrect Options:** * **B. Typhoid:** While the live-attenuated oral vaccine (Ty21a) is contraindicated, the **Injectable Polysaccharide vaccine (Vi)** is a subunit vaccine and can be administered if the risk of infection is high (e.g., travel to endemic areas). * **C. Influenza:** The **Inactivated Influenza Vaccine (IIV)** is not only safe but **strongly recommended** for all pregnant women during any trimester, as pregnancy increases the risk of severe complications from the flu. * **D. HBV (Hepatitis B):** This is a recombinant (inactivated) vaccine. It is safe and indicated for pregnant women who are at risk of acquiring HBV infection. **High-Yield Clinical Pearls for NEET-PG:** * **General Rule:** All **Live Vaccines** (BCG, MMR, Varicella, Yellow Fever, Oral Polio) are **contraindicated** in pregnancy due to the theoretical risk of fetal infection. * **Safe Vaccines:** Inactivated/Killed vaccines and Toxoids (Tetanus, Diphtheria, Pertussis) are safe. * **Mandatory in Pregnancy:** Tdap (or Tetanus Toxoid) is routinely administered to prevent neonatal tetanus. * **Exception:** If a pregnant woman is exposed to Rabies, the **Rabies vaccine** (killed) is given as post-exposure prophylaxis because the benefits far outweigh the risks.

Question 302: Carriers are important in the transmission of all the following diseases except?

A. Polio
B. Typhoid
C. Measles (Correct Answer)
D. Diphtheria

Explanation: **Explanation:** The correct answer is **Measles (Option C)**. In epidemiology, a **carrier** is an infected person who harbors a specific infectious agent without having clinical disease and serves as a potential source of infection. The absence of a carrier state in Measles is a fundamental concept in its transmission dynamics. **Why Measles is the correct answer:** Measles is characterized by the **absence of a carrier state**. An individual infected with the Measles virus either develops the clinical disease (which is highly symptomatic) or acquires immunity. There is no subclinical or chronic state where a person can shed the virus without being ill. This characteristic, along with the fact that there is no animal reservoir, makes Measles a candidate for potential eradication. **Analysis of Incorrect Options:** * **Polio:** Polio has a significant **temporary (convalescent/incubatory) and subclinical carrier state**. In fact, for every one paralytic case, there are hundreds of silent carriers who spread the virus via the feco-oral route. * **Typhoid:** *Salmonella typhi* is notorious for producing **chronic carriers** (defined as shedding the bacilli for more than one year). The bacteria often persist in the gallbladder or biliary tract (e.g., the famous case of "Typhoid Mary"). * **Diphtheria:** Diphtheria involves **nasal and throat carriers**. These carriers are more important than clinical cases in maintaining the cycle of infection within a community. **High-Yield Clinical Pearls for NEET-PG:** * **Diseases with NO carrier state:** Measles, Pertussis, Smallpox, Rabies, and Influenza. * **Chronic Carrier State:** Common in Typhoid, Hepatitis B, and Meningococcal meningitis. * **Pseudo-carrier:** A term sometimes used for those who harbor a pathogen that is not actually causing an infection (e.g., *Staph aureus* in the nares). * **Epidemiological Importance:** Diseases without a carrier state are generally easier to control through mass immunization and herd immunity.

Question 303: Which of the following is NOT transmitted by Aedes mosquitoes?

A. Dengue fever
B. Chikungunya
C. Japanese encephalitis (Correct Answer)
D. Yellow fever

Explanation: **Explanation:** The correct answer is **Japanese encephalitis (JE)** because it is primarily transmitted by the **Culex tritaeniorhynchus** mosquito, not the Aedes species. Culex mosquitoes typically breed in stagnant water, such as rice fields and ditches, and are nocturnal biters. **Analysis of Options:** * **Dengue fever:** Transmitted by *Aedes aegypti* (primary) and *Aedes albopictus*. These are "day-biters" that breed in clean, man-made containers. * **Chikungunya:** Also transmitted by *Aedes aegypti* and *Aedes albopictus*. It often presents with severe arthralgia and is frequently co-endemic with Dengue. * **Yellow fever:** Primarily transmitted by *Aedes aegypti* in urban cycles and *Haemagogus* species in jungle cycles. It is a viral hemorrhagic fever prevalent in Africa and South America. * **Japanese encephalitis:** As mentioned, the vector is **Culex**. It is a zoonotic disease where pigs and water birds (Ardeid birds) act as the main reservoirs/amplifiers. **High-Yield Clinical Pearls for NEET-PG:** 1. **Aedes Characteristics:** Known as the "Tiger Mosquito" due to white stripes; they are nervous feeders (bite multiple people to complete one meal) and breed in artificial collections of water (coolers, tires, flower pots). 2. **JE Vector:** The *Culex tritaeniorhynchus* is the most important vector in India. Man is a **dead-end host** for JE. 3. **Zika Virus:** Another important disease transmitted by *Aedes aegypti* (often tested alongside Dengue and Chikungunya). 4. **Control:** Aedes control focuses on "Source Reduction" (eliminating stagnant water containers), whereas Culex control often involves large-scale environmental management of irrigation sites.

Question 304: What is the most common cause of DALYs (Disability-Adjusted Life Years) worldwide?

A. Schizophrenia
B. Bipolar disorder (Mania)
C. Depressive disorders (Correct Answer)
D. Alzheimer's disease

Explanation: **Explanation:** **1. Why Depressive Disorders is the Correct Answer:** DALY (Disability-Adjusted Life Year) is a summary measure of population health that combines **YLL** (Years of Life Lost due to premature mortality) and **YLD** (Years Lived with Disability). According to the Global Burden of Disease (GBD) studies, **Unipolar Depressive Disorders** consistently rank as the leading cause of YLDs globally and a top contributor to total DALYs among mental and substance use disorders. Its high prevalence, early age of onset, and chronic nature make it the single largest contributor to non-fatal health loss worldwide. **2. Why Other Options are Incorrect:** * **Schizophrenia:** While Schizophrenia has a high "disability weight" (it is more severe per individual), its lower prevalence compared to depression results in a smaller total contribution to global DALYs. * **Bipolar Disorder:** Similar to schizophrenia, while it causes significant impairment, the total population-level burden is lower than that of major depressive disorders. * **Alzheimer’s Disease:** While the burden of dementia is rising rapidly due to aging populations, it currently ranks lower than depression in total DALYs, primarily because it affects a specific demographic (the elderly) rather than the broad age range affected by depression. **3. High-Yield Clinical Pearls for NEET-PG:** * **DALY Formula:** $DALY = YLL + YLD$. * **1 DALY** = One lost year of "healthy" life. * **Leading cause of DALYs (All causes):** Ischemic Heart Disease (IHD) is the leading cause of DALYs globally across all medical categories. * **Mental Health Context:** Among all mental, neurological, and substance use disorders, **Depressive Disorders** are the #1 contributor to DALYs. * **India Context:** In India, the leading cause of DALYs has shifted from communicable diseases (like Diarrhea/Lower Respiratory Infections) to **Ischemic Heart Disease**.

Question 305: Which of the following better correlates with Sullivan's index?

A. Infant mortality rate
B. Life expectancy at the age of one
C. Per capita income
D. Number of years lived without disability (Correct Answer)

Explanation: **Explanation:** **Sullivan’s Index** (also known as Disability-Free Life Expectancy) is a composite health indicator used to measure the quality of life rather than just the quantity. It is calculated by subtracting the duration of bedridden days and inability to perform major activities from the total life expectancy. Therefore, it directly represents the **number of years lived without disability (Option D)**. **Analysis of Options:** * **Option A (Infant Mortality Rate):** This is a sensitive indicator of the overall health status of a community and socio-economic development, but it does not account for the quality of life or disability in survivors. * **Option B (Life Expectancy at age one):** This is a component of the Physical Quality of Life Index (PQLI). While it measures longevity, it fails to distinguish between years lived in good health and years lived with chronic illness or disability. * **Option C (Per capita income):** This is an economic indicator (part of the Human Development Index) and does not directly measure health outcomes or disability. **High-Yield Facts for NEET-PG:** * **Sullivan’s Index formula:** Life Expectancy – Duration of disability/bedridden state. * It is considered one of the most advanced indicators of health because it combines mortality and morbidity data into a single estimate. * **PQLI (Physical Quality of Life Index):** Includes Infant Mortality Rate, Life Expectancy at Age 1, and Literacy (Scale 0-100). * **HDI (Human Development Index):** Includes Life Expectancy at Birth, Mean/Expected years of schooling, and GNI per capita. * **DALY (Disability Adjusted Life Years):** Measures the burden of disease (Years of Life Lost + Years Lived with Disability). One DALY is one lost year of "healthy" life.

Question 306: As per NFHS 3 data, what is the prevalence of anemia in children 6 to 59 months?

A. 50%
B. 60%
C. 70% (Correct Answer)
D. 80%

Explanation: **Explanation:** The National Family Health Survey (NFHS) is a critical data source for public health trends in India. According to **NFHS-3 (2005-06)**, the prevalence of anemia among children aged 6 to 59 months was recorded at **69.5%**, which is rounded to **70%** for examination purposes. Anemia in this age group is primarily attributed to nutritional deficiencies (iron, B12, and folate), poor complementary feeding practices, and high rates of parasitic infections. **Analysis of Options:** * **Option C (70%):** Correct. NFHS-3 reported that 7 out of 10 children in this age bracket were anemic. * **Option A (50%) & B (60%):** These values underestimate the severe public health burden of anemia during the NFHS-3 period. * **Option D (80%):** While anemia prevalence was high, it did not reach the 80% threshold nationally, though it may have been seen in specific high-risk pockets. **High-Yield Facts for NEET-PG:** * **Trend Analysis:** The prevalence of anemia in children has shown a fluctuating but high trend: **NFHS-3 (69.5%)** → **NFHS-4 (58.6%)** → **NFHS-5 (67.1%)**. Note the significant *increase* in anemia in the latest NFHS-5 data. * **WHO Cut-off:** For children (6–59 months), anemia is defined as Hemoglobin **<11 g/dL**. * **Anemia Mukt Bharat (AMB):** This strategy aims to reduce anemia by 3 percentage points per year. For children (6–59 months), the prophylactic dose is **1 ml of Iron & Folic Acid (IFA) syrup** (20 mg elemental Iron + 100 mcg Folic acid) bi-weekly.

Question 307: Which of the following diseases is NOT caused by a common vector?

A. Dengue fever
B. Yellow fever
C. KED (Correct Answer)
D. Japanese encephalitis

Explanation: ### Explanation The question tests your knowledge of **Arboviral diseases** and their specific vectors, a high-yield area in Epidemiology. **1. Why KED is the correct answer:** **Kyasanur Forest Disease (KFD)**—often mislabeled in shorthand as KED in some question banks—is caused by a Flavivirus. Unlike the other options, its primary vector is the **Hard Tick (*Haemaphysalis spinigera*)**. It is not transmitted by mosquitoes. It is geographically localized to the Western Ghats of India (Karnataka) and is clinically characterized by fever, headache, and hemorrhagic manifestations. **2. Analysis of Incorrect Options (Common Vector: *Aedes aegypti*):** * **Dengue Fever:** Primarily transmitted by the ***Aedes aegypti*** mosquito (the "tiger mosquito"). * **Yellow Fever:** Also transmitted by the ***Aedes aegypti*** mosquito in urban cycles. * **Japanese Encephalitis (JE):** While JE has a different mosquito vector (***Culex tritaeniorhynchus***), it is often grouped with Dengue and Yellow Fever in exams to contrast with Tick-borne or Louse-borne diseases. However, in the context of this specific question, Dengue and Yellow Fever share the *exact* same vector (*Aedes*), while JE and the others are all mosquito-borne. KFD stands out as the only **Tick-borne** disease. **3. NEET-PG High-Yield Pearls:** * **KFD (Monkey Fever):** Monkeys (*Presbytis entellus*) are the common amplifying hosts; their death is often the first sign of an outbreak. * **Aedes aegypti:** Known as a "nervous feeder" and "daytime biter." It breeds in artificial collections of clean water (coolers, tires). * **Culex:** Breeds in dirty water (paddy fields, stagnant drains). It is the vector for **JE, Filariasis, and West Nile Virus.** * **Anopheles:** Vector for **Malaria**; breeds in clean, stagnant water.

Question 308: What is a disadvantage of a case-control study when compared to a cohort study?

A. It is easy to carry out.
B. It is rapid and inexpensive.
C. It cannot measure the cause-to-effect relationship. (Correct Answer)
D. It is useful in rare diseases.

Explanation: ### Explanation **Why the correct answer is right:** The primary disadvantage of a **case-control study** is its inability to establish a definitive **temporal relationship** (cause-to-effect). In a case-control study, we start with the outcome (the disease) and look backward in time to identify exposures. Because both the exposure and the outcome have already occurred at the time the study begins, it is difficult to prove that the exposure preceded the disease. In contrast, a **cohort study** starts with a healthy population, identifies the exposure first, and follows them forward to see who develops the disease, making it the gold standard for establishing temporality and calculating **Incidence**. **Analysis of Incorrect Options:** * **A & B (Easy, Rapid, and Inexpensive):** These are actually **advantages** of case-control studies. Since they do not require long-term follow-up or large sample sizes, they are more resource-efficient than cohort studies. * **D (Useful in rare diseases):** This is another major **advantage**. Because you can specifically recruit "cases" of a rare condition, you don't have to wait years for the disease to manifest in a general population (as you would in a cohort study). **High-Yield NEET-PG Pearls:** * **Measure of Association:** Case-control studies use **Odds Ratio (OR)**; Cohort studies use **Relative Risk (RR)** and **Attributable Risk (AR)**. * **Directionality:** Case-control is **Retrospective** (Effect to Cause); Cohort is usually **Prospective** (Cause to Effect). * **Bias:** Case-control studies are highly prone to **Recall Bias** and **Selection Bias**. * **Incidence:** You **cannot** calculate Incidence from a case-control study; it can only be calculated from a cohort study.

Question 309: A case-control study is a type of:

A. Descriptive epidemiological study
B. Analytical study (Correct Answer)
C. Longitudinal study
D. Experimental epidemiological study

Explanation: **Explanation:** Epidemiological studies are broadly classified into **Observational** and **Experimental** studies. Observational studies are further divided into **Descriptive** (generating hypotheses) and **Analytical** (testing hypotheses). **Why Option B is Correct:** A **Case-Control study** is a classic example of an **Analytical study**. Its primary purpose is to test a hypothesis by determining the association between an exposure and an outcome. It works backward from effect (disease) to cause (risk factor) by comparing a group of individuals with the disease (cases) to a group without the disease (controls). **Why Other Options are Incorrect:** * **Option A (Descriptive):** These studies (e.g., Case reports, Case series, Cross-sectional surveys) only describe the distribution of disease by time, place, and person. They do not use a comparison group to test associations. * **Option C (Longitudinal):** While some define longitudinal studies as any study with a time element, in epidemiology, this term is most synonymous with **Cohort studies**, which follow a population forward in time. Case-control studies are typically retrospective. * **Option D (Experimental):** These involve active intervention by the investigator (e.g., Randomized Controlled Trials). In case-control studies, the researcher merely observes without intervening. **High-Yield Clinical Pearls for NEET-PG:** * **Direction:** Case-control studies are **Retrospective** (proceeds from effect to cause). * **Measure of Association:** The **Odds Ratio (OR)** is the key metric derived from a case-control study. * **Suitability:** It is the best study design for **rare diseases** or diseases with long latency periods. * **Bias:** They are particularly prone to **Recall Bias** and Selection Bias.

Question 310: All are true for components of DOTS, except?

A. High compliance (Correct Answer)
B. Given under observation
C. Political commitment
D. Accountability

Explanation: The **DOTS (Directly Observed Treatment, Short-course)** strategy is the internationally recommended core of the Revised National Tuberculosis Control Programme (RNTCP), now the National TB Elimination Programme (NTEP). ### **Why "High Compliance" is the Correct Answer (The Exception)** In the context of DOTS components, **High Compliance** is considered an **outcome** or a goal of the strategy, rather than a structural **component** itself. The components are the specific operational pillars required to achieve that compliance. ### **Explanation of the 5 Pillars of DOTS:** To remember the components, use the standard WHO framework: 1. **Political Commitment:** Sustained government funding and planning (Option C). 2. **Good Quality Diagnosis:** Primarily via Sputum Smear Microscopy (or newer molecular tests like CBNAAT). 3. **Uninterrupted Supply of Quality Drugs:** Ensuring no stock-outs. 4. **Directly Observed Treatment (DOT):** A trained health worker or designated provider observes the patient swallowing the medicine to ensure adherence (Option B). 5. **Systematic Recording and Reporting:** This ensures **Accountability** for every patient started on treatment (Option D). ### **Analysis of Options:** * **Option B (Observation):** This is the "DO" in DOTS. It shifts the responsibility of cure from the patient to the provider. * **Option C (Political Commitment):** This is the first and most crucial pillar for resource allocation. * **Option D (Accountability):** The standardized recording/reporting system ensures the program is accountable for the treatment outcome of every patient. ### **High-Yield Clinical Pearls for NEET-PG:** * **The "Heart" of DOTS:** Direct observation of drug intake. * **The "Brain" of DOTS:** Monitoring and supervision (Recording/Reporting). * **NTEP Update:** The program has shifted from "Intermittent" (thrice weekly) to **Daily Regimen** using Fixed-Dose Combinations (FDCs) to further improve compliance. * **Nikshay:** The web-based portal used in India for TB surveillance and accountability.

Practice by Chapter

Principles of Epidemiology

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Measures of Disease Frequency

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Epidemiological Study Designs

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Descriptive Epidemiology

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Analytical Epidemiology

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Experimental Epidemiology

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Screening for Disease

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Surveillance Systems

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Investigation of an Epidemic

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Association and Causation

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Modern Epidemiological Methods

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Critical Appraisal of Epidemiological Studies

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