Epidemiology Practice Questions

Q: Which of the following is NOT a measurement of mortality?

Incidence. **Explanation:** In epidemiology, health indicators are broadly classified into measurements of **mortality** (death) and **morbidity** (illness/disease state). **Why 'Incidence' is the correct answer:** Incidence is a measurement of **morbidity**, not mortality. It is defined as the number of *new cases* of a disease occurring in a specific population at risk during a defined period. It reflects the rate at which a disease is developing and is used to determine the etiology and efficacy of preventive measures. **Analysis of incorrect options (Mortality Indicators):** * **Crude Death Rate (CDR):** The most common mortality indicator; it measures the number of deaths per 1,000 mid-year population in a given year. * **Survival Rate:** This is the proportion of survivors in a group (usually a cohort of patients) after a specific period (e.g., 5-year survival rate for cancer). It is a direct measurement of mortality/prognosis. * **Case Fatality Rate (CFR):** This measures the killing power of a disease. It is the ratio of deaths from a specific disease to the total number of diagnosed cases of that disease. **High-Yield Clinical Pearls for NEET-PG:** * **Prevalence vs. Incidence:** Prevalence (Old + New cases) measures the total burden of disease, while Incidence (New cases only) measures the risk of contracting the disease. * **CFR vs. Mortality Rate:** CFR represents the **virulence** of an organism, whereas the Mortality Rate represents the impact of the disease on the **entire population**. * **Standardized Mortality Ratio (SMR):** Often asked in exams, SMR is used to compare the mortality experience of different populations by adjusting for age (SMR = Observed deaths / Expected deaths × 100).

Q: All of the following are analytical epidemiological studies except?

Field trial. **Explanation:** Epidemiological studies are broadly classified into two categories: **Observational** and **Experimental**. 1. **Why "Field Trial" is the correct answer:** Analytical studies are a subtype of observational studies where the investigator does not intervene but observes the relationship between exposure and outcome. **Field trials**, however, are a type of **Experimental study** (specifically, a community-based intervention). In field trials, the investigator actively assigns an intervention (like a vaccine or a nutritional supplement) to healthy individuals in the community to prevent the occurrence of disease. Since it involves an intervention, it is not classified as an analytical study. 2. **Analysis of incorrect options:** * **Cohort Study (Option A):** An analytical study that proceeds from "cause to effect." It compares an exposed group to a non-exposed group to determine the incidence of disease. * **Case-control Study (Option B):** An analytical study that proceeds from "effect to cause." It compares individuals with a disease (cases) to those without (controls) to look for past exposure. * **Ecological Study (Option C):** An analytical study where the unit of observation is a **population or group** rather than individuals. It looks for correlations between aggregate data (e.g., per capita fat consumption and heart disease rates). **High-Yield Clinical Pearls for NEET-PG:** * **Hierarchy of Evidence:** Randomized Controlled Trials (RCTs) > Cohort > Case-Control > Case Series > Case Report. * **Unit of Study:** * Ecological study: **Populations** * Case-control/Cohort: **Individuals** * Field trials: **Healthy individuals** * Community trials: **Communities** * **Measure of Association:** Cohort studies use **Relative Risk (RR)**, while Case-control studies use **Odds Ratio (OR)**.

Q: Which type of disease occurrence trend shows changes over a long period of time?

Secular trend. **Explanation:** The question refers to the classification of **time trends** in disease occurrence, which is a fundamental concept in descriptive epidemiology. **1. Why "Secular Trend" is correct:** A **Secular Trend** refers to progressive changes in the occurrence of a disease over a **long period of time** (usually decades). These trends reflect consistent increases or decreases in disease frequency. * *Example:* The consistent decline of Tuberculosis or Polio over several decades, or the steady rise of non-communicable diseases like Diabetes and Lung Cancer in the 21st century. **2. Why the other options are incorrect:** * **Cyclic Trend:** These are periodic fluctuations in disease frequency that occur over several years (e.g., 2–3 years). They are often seen in diseases where herd immunity builds up and then wanes, such as Measles or Rubella in the pre-vaccination era. * **Seasonal Trend:** These occur within a single year and are related to environmental or behavioral factors. For example, Gastrointestinal infections peak in summer/monsoon, while Respiratory infections (like Influenza) peak in winter. * **Short-term Fluctuations:** These refer to sudden spikes in cases over a very brief period (hours, days, or weeks), typically seen in **epidemics** (e.g., a food poisoning outbreak). **High-Yield Clinical Pearls for NEET-PG:** * **Point Source Epidemic:** All cases occur within one incubation period (e.g., Bhopal Gas Tragedy). * **Propagated Epidemic:** Shows a gradual rise and fall; spreads from person to person (e.g., COVID-19, Hepatitis A). * **Leading Indicator:** Secular trends are the most reliable indicators for long-term health planning and policy evaluation.

Q: Which model is represented by the epidemiologic web of causation theme?

McMahon and Pugh. **Explanation:** The **Web of Causation** is a fundamental concept in modern epidemiology used to explain the etiology of complex, multi-factorial diseases (especially non-communicable diseases like cardiovascular disease or cancer). 1. **Why McMahon and Pugh is correct:** The term "Web of Causation" was first suggested by **Brian MacMahon and Thomas Pugh** in 1970. This model moved away from the simplistic "one germ, one disease" theory. It posits that effects never depend on a single isolated cause but develop through a complex chain of interconnected factors (biological, social, environmental, and behavioral) that link together like a web. 2. **Why other options are incorrect:** * **Louis Pasteur & Robert Koch:** Both were pioneers of the **Germ Theory of Disease**. They proposed the "Single Cause" or "Monocausal" model, which suggests that every disease is caused by a specific pathogenic microorganism. While revolutionary for infectious diseases, this model failed to explain chronic lifestyle diseases. * **Robert Koch** specifically developed "Koch’s Postulates" to establish a causal relationship between a microbe and a disease. **High-Yield Clinical Pearls for NEET-PG:** * **Epidemiological Triad:** Agent, Host, and Environment (primarily for infectious diseases). * **Multifactorial Causation:** Pettenkofer’s theory; it suggests that disease is caused by multiple factors, not just a single agent. * **BEINGS Model:** A mnemonic for the spectrum of disease determinants (Biological, Behavioral, Environmental, Immunological, Nutritional, Genetic, Social/Spiritual). * **Wheel Theory:** Emphasizes the importance of the host-environment relationship, with a genetic core at the center.

Q: Which of the following statements about bleaching powder is true?

It is not used for disinfection of faces and urine.. ### Explanation **Bleaching Powder (Chlorinated Lime)** is a widely used disinfectant in public health, but its efficacy is highly dependent on its chemical stability and the presence of organic matter. **Why Option D is Correct:** Bleaching powder is **not** recommended for the disinfection of feces and urine. This is because chlorine is rapidly neutralized by organic matter. Feces and urine contain high concentrations of organic compounds that "consume" the available chlorine, rendering it ineffective unless used in impractical quantities. For excreta disinfection, **Cresol** or **8% Lime (Calcium Hydroxide)** are preferred. **Analysis of Incorrect Options:** * **Option A:** Fresh bleaching powder contains approximately **33% available chlorine**, not 100%. This is a high-yield number for exams. * **Option B:** There is no "100% solution" of bleaching powder. For general environmental disinfection, a 1% solution is typically used. For feces, even if it were used, the concentration required would be much higher, but it remains suboptimal due to the organic load. * **Option C:** Bleaching powder is **unstable**. It loses its chlorine content rapidly when exposed to air, light, or moisture. It must be stored in a cool, dark, and dry place in airtight containers. **High-Yield NEET-PG Pearls:** 1. **Horrocks’s Apparatus:** Used to estimate the dose of bleaching powder required to disinfect a given quantity of water. 2. **Contact Time:** For effective water disinfection, the contact time for chlorine should be at least **30 to 60 minutes**. 3. **Free Residual Chlorine:** The recommended level in drinking water is **0.5 mg/L** after 1 hour of contact. 4. **OT Test (Orthotolidine):** Used to detect both free and combined chlorine; however, the **OTA (Orthotolidine-Arsenite) Test** is superior as it distinguishes between the two.

Q: Prepatent period in lymphatic filariasis is defined as the time interval between inoculation of infective larvae and which of the following?

First appearance of detectable microfilaria. ### Explanation In epidemiology and parasitology, the **Prepatent Period** is defined as the time interval between the entry of the infective stage of a parasite into the host and the earliest time at which its presence can be demonstrated by diagnostic stages (such as eggs or larvae) in the blood, excreta, or tissues. In the context of **Lymphatic Filariasis**: * **Correct Answer (B):** The prepatent period ends when **microfilariae (mf)** first appear in the peripheral blood. For *Wuchereria bancrofti*, this period typically lasts about **8 to 12 months**. #### Analysis of Incorrect Options: * **A & C (Blockage of lymphatics/Lymphoedema):** These represent the **Incubation Period**, which is the interval between infection and the onset of clinical signs and symptoms. In filariasis, the incubation period is usually longer than the prepatent period (often 8–16 months). * **D (Development of adult worm):** While the larvae must mature into adult worms to produce microfilariae, the definition of "prepatent" specifically relies on the **detection** of the next generation (microfilariae) in the blood, not just the maturation of the adult. #### High-Yield NEET-PG Pearls: * **Infective Stage:** L3 Larva (introduced by the bite of an infected mosquito). * **Diagnostic Stage:** Microfilariae (detected via peripheral blood smear, usually at night due to nocturnal periodicity). * **Biological Incubation Period:** Another term for the Prepatent Period. * **Clinical Incubation Period:** Time from infection to the first clinical symptom (e.g., filarial fever). * **Drug of Choice:** Diethylcarbamazine (DEC) is the standard treatment, but it is contraindicated in patients with heavy Onchocerciasis or Loiasis co-infections.

Question 1

Which of the following is NOT a measurement of mortality?

Accepted Answer

Incidence

Answer

Crude death rate

Answer

Survival rate

Answer

Case fatality rate

Question 2

Screening for breast cancer using mammography is considered a form of:

Accepted Answer

Secondary prevention

Answer

Primordial prevention

Answer

Primary prevention

Answer

Tertiary prevention

Question 3

All of the following are analytical epidemiological studies except?

Accepted Answer

Field trial

Answer

Cohort study

Answer

Case-control study

Answer

Ecological study

Question 4

Relative risk can be calculated by:

Accepted Answer

Incidence of disease amongst exposed/incidence of disease amongst non-exposed

Answer

Incidence of disease amongst non-exposed/ incidence of disease amongst exposed

Answer

Incidence of disease amongst exposed/total population of that area

Answer

Incidence of disease amongst non-exposed/total population of that area

Question 5

To study the incidence of malaria according to various age and sex groups in a village, what type of study is needed?

Accepted Answer

Descriptive study

Answer

Case-control study

Answer

Cohort study

Answer

Experimental study

Question 6

Regarding standardization of death rates, which of the following statements is FALSE?

Accepted Answer

Age-specific death rates are not needed for standardization.

Answer

A standard population is required for standardization.

Answer

The populations being compared should be comparable.

Answer

Standardization involves comparing two populations.

Question 7

Which type of disease occurrence trend shows changes over a long period of time?

Accepted Answer

Secular trend

Answer

Cyclic trend

Answer

Seasonal trend

Answer

Short-term fluctuations

Question 8

Which model is represented by the epidemiologic web of causation theme?

Accepted Answer

McMahon and Pugh

Answer

Louis Pasteur

Answer

Robert Koch

Answer

None of the above

Question 9

Which of the following statements about bleaching powder is true?

Accepted Answer

It is not used for disinfection of faces and urine.

Answer

It contains 100% available chlorine.

Answer

A 100% solution is used for disinfection of faces.

Answer

It is a stable compound on storage.

Question 10

Prepatent period in lymphatic filariasis is defined as the time interval between inoculation of infective larvae and which of the following?

Accepted Answer

First appearance of detectable microfilaria

Answer

Blockage of lymphatics

Answer

Development of lymphoedema

Answer

Development of adult worm

Epidemiology — MCQs

Epidemiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?