Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 141: A 7-year-old child presents with a dog bite from the neighborhood. On examination, there is a small superficial abrasion without oozing of blood. How would you classify this bite?

A. Category 1
B. Category 2 (Correct Answer)
C. Category 3
D. Category 4

Explanation: ### Explanation The classification of dog bites is based on the **WHO Rabies Exposure Categories**, which determine the required post-exposure prophylaxis (PEP). **Why Category 2 is correct:** Category 2 exposure is defined as **minor scratches or abrasions without bleeding**, or nibbling of uncovered skin. In this case, the child has a superficial abrasion without oozing of blood, which fits the criteria perfectly. * **Management:** Immediate local wound washing and administration of the Anti-Rabies Vaccine (ARV). Rabies Immunoglobulin (RIG) is generally not required for Category 2. **Analysis of Incorrect Options:** * **Category 1:** This involves touching or feeding animals, or licks on intact skin. Since there is an abrasion (break in skin), it cannot be Category 1. No treatment is required. * **Category 3:** This involves single or multiple transdermal bites/scratches with **bleeding**, licks on broken skin, or contamination of mucous membranes with saliva (e.g., licks on eyes/mouth). It also includes all exposures to bats. * **Category 4:** There is no "Category 4" in the WHO classification for rabies exposure. **High-Yield Clinical Pearls for NEET-PG:** 1. **Wound Management:** The most important first step is washing the wound with soap and running water for at least **15 minutes**. 2. **RIG Rule:** Category 3 exposures require **both** ARV and Rabies Immunoglobulin (RIG). RIG should be infiltrated into and around the wound. 3. **Site of Injection:** ARV is given Intramuscularly (Deltoid) or Intradermally. **Never** give the vaccine in the gluteal region as fat reduces vaccine efficacy. 4. **Suturing:** Avoid suturing rabies-infected wounds. If necessary, it should be done only after RIG infiltration and delayed by 24–48 hours.

Question 142: What is the sex ratio?

A. Number of males per 100 females
B. Number of males per 1000 females
C. Number of females per 100 males
D. Number of females per 1000 males (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** In demography and public health, the **Sex Ratio** is a key indicator used to measure the balance between males and females in a population. In the Indian context (and for the NEET-PG exam), it is defined as the **number of females per 1,000 males**. This is an "indirect ratio" where the denominator is fixed at 1,000 to provide a standardized measure for comparing different geographical regions or time periods. **2. Why Other Options are Incorrect:** * **Options A & B:** These represent the "Masculinity Proportion" or the sex ratio as defined in many Western countries (where it is often expressed as males per 100 females). However, Indian census methodology specifically uses females as the numerator. * **Option C:** While this uses the correct numerator (females), the multiplier is 100. In large-scale population studies like the Census, a multiplier of 1,000 is used to ensure precision and capture smaller demographic shifts. **3. NEET-PG High-Yield Clinical Pearls:** * **Child Sex Ratio (CSR):** Defined as the number of females per 1,000 males in the **0–6 years** age group. This is a sensitive indicator of female feticide and neglect. * **Census 2011 Data:** The overall sex ratio in India was **943** females per 1,000 males. The Child Sex Ratio was **919**. * **Highest/Lowest:** According to the 2011 Census, **Kerala** had the highest sex ratio (1084), while **Haryana** had the lowest (879) among states. * **NFHS-5 Data:** Recent National Family Health Survey (NFHS-5) trends suggest a shift, showing 1,020 females per 1,000 males, though Census data remains the primary gold standard for exam questions unless specified otherwise.

Question 143: In an outbreak of cholera in a village of 2000 population, 20 cases have occurred and 5 died. What is the case fatality rate?

A. 1%
B. 0.25%
C. 5%
D. 25% (Correct Answer)

Explanation: ### Explanation **1. Understanding the Correct Answer (D: 25%)** The **Case Fatality Rate (CFR)** is a measure of the severity of a disease. It represents the proportion of people diagnosed with a specific disease who die from it within a specified period. The formula for CFR is: $$\text{CFR} = \frac{\text{Total number of deaths due to a disease}}{\text{Total number of cases of the same disease}} \times 100$$ In this scenario: * Total deaths = 5 * Total cases = 20 * Calculation: $(5 / 20) \times 100 = \mathbf{25\%}$ **2. Why the Incorrect Options are Wrong** * **Option A (1%):** This is the **Cause-Specific Mortality Rate** (Total deaths / Total population $\times 100$), which is $(5 / 2000) \times 100 = 0.25\%$, not 1%. * **Option B (0.25%):** This represents the **Mortality Rate** (or Cause-Specific Death Rate) for the village. It incorrectly uses the total population as the denominator instead of the number of cases. * **Option C (5%):** This is the **Attack Rate** (Total cases / Total population at risk $\times 100$), which is $(20 / 2000) \times 100 = 1\%$. 5% is a mathematical distractor. **3. High-Yield Clinical Pearls for NEET-PG** * **CFR vs. Mortality Rate:** CFR is a **ratio** (though expressed as a percentage) and measures the **killing power** of a disease. Mortality rate is a **rate** and measures the risk of dying in the general population. * **Denominator:** Always remember that for CFR, the denominator is the **number of cases**, not the total population. * **Cholera Fact:** Without treatment, the CFR of Cholera can be as high as 50%; with prompt rehydration therapy, it can be reduced to less than 1%. * **Disease Severity:** CFR is the best indicator of the virulence of an infectious agent and the efficacy of treatment.

Question 144: All of the following are true regarding acute attack of Polio, except?

A. Fecal sample is carried in a cold box.
B. Three consecutive stool samples are positive. (Correct Answer)
C. Investigation is done within 48 hours.
D. Throat swab is taken for diagnosis.

Explanation: ### Explanation **Why Option B is the Correct Answer (The "Except" Statement):** In the surveillance of Acute Flaccid Paralysis (AFP) for Polio, the standard protocol requires **two** "adequate" stool samples, not three. These samples must be collected **24 to 48 hours apart** and within **14 days** of the onset of paralysis. A single positive sample is sufficient for a diagnosis; it is not a requirement for all consecutive samples to be positive to confirm the case. **Analysis of Other Options:** * **Option A:** Poliovirus is thermolabile. To maintain the "Reverse Cold Chain," stool samples must be transported at **2–8°C** in a cold box with ice packs to ensure the virus remains viable for culture. * **Option C:** Rapid notification is critical. Under the Global Polio Eradication Initiative, an AFP case should ideally be investigated within **48 hours** of reporting to ensure timely sample collection and contact tracing. * **Option D:** While stool is the primary specimen for surveillance due to prolonged viral shedding (up to 6 weeks), the poliovirus can be isolated from **throat swabs** during the first week of the illness (pre-paralytic and early paralytic phases). **High-Yield Clinical Pearls for NEET-PG:** * **AFP Surveillance:** The gold standard for Polio diagnosis is the isolation of the Wild Poliovirus (WPV) from stool in a WHO-accredited laboratory. * **Reverse Cold Chain:** This refers to the process of transporting clinical specimens from the field to the laboratory under cold conditions (the opposite of vaccine delivery). * **Stool Sample Criteria:** "Adequate" samples mean 2 samples, collected 24 hours apart, within 14 days of onset, arriving at the lab in good condition (no leakage/desiccation) with ice present. * **Most Common Site of Paralysis:** Spinal Polio typically affects the **lower limbs** asymmetrically (proximal muscles more than distal).

Question 145: In which of the following diseases is overall survival increased by a screening procedure?

A. Prostate cancer
B. Lung cancer
C. Colon cancer (Correct Answer)
D. Ovarian cancer

Explanation: **Explanation:** The primary goal of a screening program is to reduce mortality by detecting a disease at a pre-symptomatic stage where treatment is more effective. **Why Colon Cancer is Correct:** Colon cancer screening (via colonoscopy or fecal occult blood testing) is highly effective because it identifies **pre-cancerous lesions (adenomatous polyps)**. Removing these polyps prevents the progression to invasive malignancy. Furthermore, detecting colorectal cancer at an early stage significantly improves the 5-year survival rate (approx. 90%) compared to late-stage detection. It is one of the few screening procedures proven to reduce both disease-specific and overall mortality. **Analysis of Incorrect Options:** * **Prostate Cancer:** Screening (PSA testing) often leads to **overdiagnosis** of slow-growing tumors that would never have caused symptoms during the patient's lifetime. While it may increase "lead-time" survival, it has not consistently shown a significant increase in overall survival in large trials. * **Lung Cancer:** While Low-Dose CT (LDCT) is recommended for high-risk smokers, it has a high false-positive rate. Historically, screening with chest X-rays or sputum cytology failed to improve overall survival. * **Ovarian Cancer:** There is currently no effective screening tool (including CA-125 and ultrasound) that has been proven to reduce mortality or increase overall survival, as the disease is often already metastatic at the time of detection. **High-Yield Clinical Pearls for NEET-PG:** * **Lead-time bias:** An apparent increase in survival time because the disease was detected earlier, without actually delaying the time of death. * **Length bias:** Screening tends to detect slow-growing, less aggressive cases, making the screening look more effective than it is. * **Wilson and Jungner Criteria:** The gold standard criteria used to decide if a disease should be screened. * **Screening vs. Diagnostic Test:** Screening is done on apparently healthy populations; diagnostic tests are for those with symptoms.

Question 146: Regarding point source epidemics, which statement is true?

A. Rapid rise and fall in cases (Correct Answer)
B. Caused only by infections
C. Characterized by explosive spread
D. Associated with a high secondary attack rate

Explanation: ### Explanation In epidemiology, a **Point Source Epidemic** occurs when a group of susceptible individuals is exposed to a specific pathogen or toxin simultaneously or over a very short period. **1. Why Option A is Correct:** Because the exposure is simultaneous and brief, all cases occur within one incubation period of the disease. This results in a characteristic **"log-normal" epidemic curve** featuring a **rapid rise and a rapid fall** in the number of cases. The curve is typically positively skewed. **2. Analysis of Incorrect Options:** * **Option B (Caused only by infections):** Incorrect. Point source epidemics can be non-infectious, such as the Bhopal Gas Tragedy (toxic chemical leak) or Minamata disease (mercury poisoning). * **Option C (Characterized by explosive spread):** While the rise is rapid, "explosive spread" is a term more accurately associated with **Common Source, Continuous Exposure** or **Propagated Epidemics** where the source remains active or spreads person-to-person. * **Option D (High secondary attack rate):** Incorrect. A hallmark of point source epidemics is that there is **no person-to-person transmission**. Therefore, the secondary attack rate is typically **zero**. High secondary attack rates are characteristic of Propagated (Communicable) epidemics. **3. NEET-PG High-Yield Pearls:** * **Epidemic Curve:** Look for a sharp peak and a single incubation period. * **Secondary Attack Rate (SAR):** Always zero in a pure point source epidemic (e.g., food poisoning at a single wedding). * **Examples:** Food poisoning (Staphylococcal), Bhopal Gas Tragedy, Hiroshima atomic bombing. * **Key Distinction:** If the exposure continues over time (e.g., a contaminated well), it becomes a **Continuous Common Source Epidemic**, and the curve will have a plateau rather than a sharp peak.

Question 147: Absolute contraindications to pertussis vaccine include all of the following except?

A. Static neurological disease (Correct Answer)
B. Progressive neurological disease
C. Anaphylaxis after previous dose
D. Encephalopathy within seven days of previous dose

Explanation: ### Explanation The pertussis vaccine (typically administered as DTwP or DTaP) is known for its reactogenicity. Distinguishing between absolute contraindications and mere precautions is high-yield for NEET-PG. **1. Why "Static Neurological Disease" is the correct answer:** A **static neurological disease** (e.g., stable cerebral palsy, well-controlled seizures, or developmental delay) is **not** a contraindication to the pertussis vaccine. Children with these conditions can safely receive the vaccine because their condition is not evolving, and the vaccine will not aggravate the underlying pathology. **2. Analysis of Incorrect Options (Absolute Contraindications):** * **Progressive Neurological Disease (B):** Conditions like infantile spasms, uncontrolled epilepsy, or progressive encephalopathy are absolute contraindications. Vaccination should be deferred until the neurological status is stabilized to avoid diagnostic confusion between vaccine side effects and disease progression. * **Anaphylaxis (C):** Any immediate severe allergic reaction following a previous dose of the vaccine or to any vaccine component is a universal absolute contraindication. * **Encephalopathy (D):** If encephalopathy (e.g., coma, prolonged seizures, altered consciousness) occurs within **7 days** of a previous pertussis dose that is not attributable to another cause, further doses of pertussis-containing vaccines are strictly contraindicated. **3. Clinical Pearls for NEET-PG:** * **Precautions (Not Contraindications):** Fever >40.5°C (105°F), collapse/shock-like state (Hypotonic Hyporesponsive Episode), or persistent inconsolable crying (>3 hours) within 48 hours of a previous dose are considered **precautions**. In these cases, the risk-benefit ratio must be assessed. * **DT vs. DPT:** If pertussis is contraindicated, the immunization series should be completed using the **DT (Diphtheria and Tetanus)** vaccine. * **Acellular vs. Whole-cell:** DTaP (Acellular) has a lower incidence of systemic side effects compared to DTwP (Whole-cell) but follows the same contraindication profile regarding encephalopathy.

Question 148: Which of the following diseases is an example of the 'iceberg phenomenon'?

A. Rabies
B. Measles
C. Tetanus
D. Influenza (Correct Answer)

Explanation: ### **Explanation** The **Iceberg Phenomenon of Disease** is a concept in epidemiology that describes the distribution of a disease in a community. The **tip of the iceberg** represents what the clinician sees (symptomatic, diagnosed, or hospitalized cases), while the **submerged portion** represents the hidden mass of the disease (asymptomatic, subclinical, or undiagnosed cases). #### **Why Influenza is Correct** **Influenza** is a classic example of the iceberg phenomenon. For every patient who presents with severe symptoms or is hospitalized (the tip), there are numerous individuals in the community who have mild, "flu-like" symptoms or are completely asymptomatic (the submerged portion). These hidden cases act as a reservoir, facilitating the rapid spread of the virus. #### **Analysis of Incorrect Options** * **Rabies:** This disease does **not** show the iceberg phenomenon. It is a "clinical" disease where almost every infected individual develops symptoms, and the case fatality rate is nearly 100%. There are no asymptomatic carriers. * **Measles:** Measles is highly infectious and typically presents with a distinct clinical picture (fever, cough, Koplik spots, rash). Subclinical cases are rare, meaning the "tip" represents almost the entire burden of the disease. * **Tetanus:** Tetanus is a non-communicable infectious disease. It does not have a "submerged" carrier state in the population that spreads the infection to others; it is an all-or-none clinical manifestation. #### **High-Yield Clinical Pearls for NEET-PG** * **Diseases showing Iceberg Phenomenon:** Hypertension, Diabetes Mellitus, Malnutrition, Anemia, Polio, Hepatitis A & B, and Influenza. * **Diseases NOT showing Iceberg Phenomenon:** Rabies, Measles, Tetanus, and Rubella. * **The "Waterline":** Represents the demarcation between apparent (clinical) and inapparent (subclinical) cases. * **Epidemiological Significance:** The submerged portion (carriers/subclinical cases) is more important for the **Epidemiologist** (as they are the hidden sources of infection), while the tip is the focus of the **Clinician**.

Question 149: Which stage of the demographic cycle is characterized by a declining death rate while the birth rate remains high?

A. Birth rate is lower than the death rate
B. High birth rate and high death rate
C. Death rate starts to decline which birth rate is the same (Correct Answer)
D. Death rate further declines and birth rate also falls

Explanation: ### Explanation The **Demographic Cycle** describes the historical transition of a population from high birth and death rates to low birth and death rates as a country develops. **1. Why the Correct Answer is Right:** The stage described is **Stage 2: Early Expanding**. In this stage, the death rate begins to decline due to improvements in food supply, sanitation, and basic healthcare. However, the birth rate remains high because social norms and lack of contraception take longer to change. This gap between a high birth rate and a falling death rate leads to an **"explosive" increase** in population size. **2. Analysis of Incorrect Options:** * **Option A (Birth rate lower than death rate):** This describes **Stage 5: Declining**. Here, the population actually decreases (e.g., Germany, Hungary). * **Option B (High birth rate and high death rate):** This is **Stage 1: High Stationary**. The population remains stable because the high number of births is cancelled out by high mortality (e.g., India before 1920). * **Option D (Death rate further declines and birth rate also falls):** This is **Stage 3: Late Expanding**. While the population is still growing, the rate of growth slows down as birth rates begin to drop (e.g., India is currently in this stage). **3. High-Yield NEET-PG Pearls:** * **India’s Status:** India is currently in **Stage 3 (Late Expanding)**. * **Stage 4 (Low Stationary):** Characterized by low birth and low death rates (e.g., USA, UK). * **Key Indicator:** The "Natural Increase" of a population is the difference between the birth rate and the death rate. * **Demographic Gap:** The maximum gap between birth and death rates occurs at the end of Stage 2 and the beginning of Stage 3.

Question 150: All of the following are arthropod-borne diseases except:

A. Malaria
B. Filariasis
C. Dengue
D. Dracunculosis (Correct Answer)

Explanation: **Explanation:** The core concept of this question lies in distinguishing between diseases transmitted by **arthropod vectors** (insects, arachnids) and those transmitted via **water-borne intermediate hosts**. **Why Dracunculosis is the correct answer:** Dracunculosis (Guinea worm disease) is **not** an arthropod-borne disease. It is a water-borne parasitic infection caused by *Dracunculus medinensis*. It is transmitted by drinking water containing **Cyclops** (water fleas). While Cyclops is a crustacean, it acts as an **intermediate host** in water, not a vector that actively bites or deposits the pathogen onto a human host. * *Note:* India was certified free of Dracunculosis by the WHO in February 2000. **Why the other options are incorrect:** * **Malaria:** A classic arthropod-borne disease transmitted by the bite of an infected female **Anopheles mosquito**. * **Filariasis:** Transmitted by various mosquito vectors, most commonly **Culex quinquefasciatus** (for *Wuchereria bancrofti*). * **Dengue:** A viral disease transmitted by the **Aedes aegypti** mosquito. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cyclops** is the intermediate host for: Dracunculosis, Fish Tapeworm (*Diphyllobothrium latum*), and Gnathostomiasis. 2. **Biological Transmission types:** * *Propagative:* Plague (bacilli multiply in flea). * *Cyclo-propagative:* Malaria (parasite multiplies and changes stages in mosquito). * *Cyclo-developmental:* Filariasis (parasite changes stages but does not multiply in mosquito). 3. **Extrinsic Incubation Period:** The time required for the pathogen to develop inside the arthropod vector before it becomes infective to humans.

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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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