Epidemiology Practice Questions

Q: 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?

Category 2. ### 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.

Q: What is the sex ratio?

Number of females per 1000 males. ### 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.

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

25%. ### 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.

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

Three consecutive stool samples are positive.. ### 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).

Q: Regarding point source epidemics, which statement is true?

Rapid rise and fall in cases. ### 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.

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

Death rate starts to decline which birth rate is the same. ### 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.

Q: All of the following are arthropod-borne diseases except:

Dracunculosis. **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.

Question 1

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?

Accepted Answer

Category 2

Answer

Category 1

Answer

Category 3

Answer

Category 4

Question 2

What is the sex ratio?

Accepted Answer

Number of females per 1000 males

Answer

Number of males per 100 females

Answer

Number of males per 1000 females

Answer

Number of females per 100 males

Question 3

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

Accepted Answer

25%

Answer

1%

Answer

0.25%

Answer

5%

Question 4

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

Accepted Answer

Three consecutive stool samples are positive.

Answer

Fecal sample is carried in a cold box.

Answer

Investigation is done within 48 hours.

Answer

Throat swab is taken for diagnosis.

Question 5

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

Accepted Answer

Colon cancer

Answer

Prostate cancer

Answer

Lung cancer

Answer

Ovarian cancer

Question 6

Regarding point source epidemics, which statement is true?

Accepted Answer

Rapid rise and fall in cases

Answer

Caused only by infections

Answer

Characterized by explosive spread

Answer

Associated with a high secondary attack rate

Question 7

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

Accepted Answer

Static neurological disease

Answer

Progressive neurological disease

Answer

Anaphylaxis after previous dose

Answer

Encephalopathy within seven days of previous dose

Question 8

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

Accepted Answer

Influenza

Answer

Rabies

Answer

Measles

Answer

Tetanus

Question 9

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

Accepted Answer

Death rate starts to decline which birth rate is the same

Answer

Birth rate is lower than the death rate

Answer

High birth rate and high death rate

Answer

Death rate further declines and birth rate also falls

Question 10

All of the following are arthropod-borne diseases except:

Accepted Answer

Dracunculosis

Answer

Malaria

Answer

Filariasis

Answer

Dengue

Epidemiology — MCQs

Epidemiology — MCQs

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