Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1641: There has been a gradual increase in number of non-communicable disease cases as compared to previous years. This trend is called:

A. Periodical
B. Cyclical
C. Seasonal
D. Secular (Correct Answer)

Explanation: ***Secular*** - A **secular trend** refers to a long-term change or trend in the frequency of a disease or health condition over an extended period, often years or decades. - The gradual increase in the number of non-communicable disease cases over previous years is a classic example of a **secular trend**. *Periodical* - **Periodical** variations typically refer to patterns that repeat at regular intervals but are much shorter than long-term secular trends (e.g., daily, weekly). - This term does not capture the **long-term, evolving nature** of the health trend described. *Cyclical* - A **cyclical trend** describes fluctuations in disease incidence that occur over periods longer than a year, but still demonstrate a predictable, repeating cycle, often related to socioeconomic or environmental factors (e.g., a disease peaking every few years). - While it describes patterns, it implies **repetition** rather than a continuous, unidirectional increase over time. *Seasonal* - **Seasonal trends** describe variations in disease occurrence that are related to specific seasons of the year, such as the increase in influenza cases during winter. - This term specifically refers to **annual fluctuations** and does not describe a gradual increase over many years.

Question 1642: True about epidemiology of cholera-

A. Food can transmit the disease (Correct Answer)
B. Boiling water cannot destroy the organism
C. Vaccination gives 90% protection
D. Cholera cannot be transmitted by contaminated water

Explanation: ***Food can transmit the disease*** - Cholera is commonly transmitted through the **fecal-oral route**, and **contaminated food** is a significant vehicle for this transmission. - Food can become contaminated when handled by infected individuals or prepared with **contaminated water**. *Boiling water cannot destroy the organism* - **Boiling water** for at least one minute is a highly effective method for killing Vibrio cholerae, the bacterium responsible for cholera. - High temperatures denature proteins and disrupt the cellular structure of the bacteria, rendering it inactive. *Vaccination gives 90% protection* - Oral cholera vaccines typically provide **modest protection**, ranging from 50% to 85% for a limited duration, usually around 2-5 years. - No vaccine offers 90% protection against cholera, and protection wanes over time, necessitating booster doses or revaccination. *Cholera cannot be transmitted by contaminated water* - **Contaminated water** is the primary mode of cholera transmission. - Drinking water contaminated with **Vibrio cholerae**, often from feces of infected individuals, is the most common cause of outbreaks.

Question 1643: Which of the following studies has given coronary risk factors?

A. Framingham (Correct Answer)
B. Stanford study
C. MONICA
D. North Karelia

Explanation: ***Framingham*** - The **Framingham Heart Study** is a landmark prospective cohort study that has identified many of the well-known **risk factors for cardiovascular disease**, including hypertension, high cholesterol, smoking, and diabetes. - This ongoing study, started in 1948, has been instrumental in shaping our understanding of **coronary artery disease** development and prevention strategies. *North Karelia* - The **North Karelia Project** was a comprehensive community-based prevention program in Finland that successfully reduced cardiovascular disease risk factors. - While influential in demonstrating how to **implement prevention strategies**, it applied already-known risk factors rather than discovering new ones. - The program focused on reducing smoking, cholesterol, and blood pressure in the population. *Stanford study* - While Stanford University has conducted numerous influential medical studies, there isn't a single "Stanford study" primarily recognized for giving us the comprehensive list of coronary risk factors. - Many institutions contribute to medical knowledge, but the **Framingham Heart Study** stands out for this specific contribution. *MONICA* - The **MONICA (Monitoring Trends and Determinants in Cardiovascular Disease)** Project was a multinational WHO project that aimed to monitor cardiovascular disease trends and determinants. - While it provided valuable data on the **epidemiology of cardiovascular disease** and its risk factors, it primarily assessed trends in established risk factors rather than initially identifying them.

Question 1644: Species of Anopheles causing malaria in Andaman & Nicobar island?

A. Anopheles dirus
B. Anopheles stephensi
C. Anopheles culicifacies
D. Anopheles epiroticus (Correct Answer)

Explanation: ***Anopheles epiroticus (formerly Anopheles sundaicus)*** - **Anopheles epiroticus** is the **primary malaria vector in the Andaman & Nicobar Islands**. - It belongs to the **Anopheles sundaicus complex** and is highly adapted to **coastal and island ecosystems**. - It breeds in **brackish water** and is an efficient vector for both **Plasmodium falciparum** and **Plasmodium vivax**. - This species is characteristic of **coastal Southeast Asia** and island territories. *Anopheles dirus* - **Anopheles dirus** is a primary vector in **forest-fringed areas** of mainland Southeast Asia and northeastern India. - While it is an efficient malaria vector, it is **not the predominant species** in the Andaman & Nicobar Islands. - It typically breeds in **shaded pools** in forested areas. *Anopheles stephensi* - **Anopheles stephensi** is a major **urban and rural** malaria vector in mainland India and the Middle East. - It is adapted to **urban environments** and breeds in artificial containers. - It is **not found** in the Andaman & Nicobar Islands. *Anopheles culicifacies* - **Anopheles culicifacies** is the most widespread rural malaria vector in the **Indian subcontinent**. - It breeds in **rice fields**, irrigation channels, and other shallow freshwater bodies. - It is **not present** in the Andaman & Nicobar Islands due to the distinct island ecology.

Question 1645: Index for estimating epidemic of plague?

A. Burrow index
B. Cheopis index (Correct Answer)
C. Total flea index
D. None of the options

Explanation: ***Cheopis index*** - This index is specifically used to assess the potential for a **plague outbreak** by measuring the average number of **Xenopsylla cheopis (oriental rat flea)** per rat. - A value of **1 or more** indicates a high risk of plague transmission. *Burrow index* - The burrow index is used to estimate rodent population density by counting **active burrows**. - While relevant to rodent control, it does not directly measure the **flea burden specific to plague transmission**. *Total flea index* - The total flea index is the average number of **all flea species** per rodent. - While it gives a general idea of flea infestation, it's not as specific as the Cheopis index for **plague transmission risk**, which primarily involves **X. cheopis**. *None of the options* - The **Cheopis index** is a well-established and widely used epidemiological tool for assessing plague risk. - Therefore, there is a correct option among the choices provided.

Question 1646: Key indicator for AFP surveillance?

A. At least one case of non-polio AFP per year per 100000 population of under 15 years (Correct Answer)
B. At least one case of non-polio AFP per year per 1000 population of under 5 years
C. At least one case of non-polio AFP per year per 10000 population of under 15 years
D. At least one case of non-polio AFP per year per 100000 population of under 5 years

Explanation: ***At least one case of non-polio AFP per year per 100000 population of under 15 years*** - This indicator, often referred to as the **non-polio AFP rate**, is a crucial measure for assessing the sensitivity and effectiveness of **Acute Flaccid Paralysis (AFP) surveillance**. - A rate of at least 1 non-polio AFP case per 100,000 population under 15 years acts as a **robust benchmark** to ensure that the surveillance system is sensitive enough to detect all potential polio cases. *At least one case of non-polio AFP per year per 1000 population of under 5 years* - This option incorrectly modifies both the **population denominator** (1,000 instead of 100,000) and the **age group** (under 5 years instead of under 15 years) for standard AFP surveillance. - While children under 5 are a high-risk group for polio, the surveillance target is broader to capture all AFP cases, and the benchmark rate is specific to a larger population denominator. *At least one case of non-polio AFP per year per 10000 population of under 15 years* - This option uses an incorrect **population denominator** of 10,000, which would suggest a surveillance system that is less sensitive than the established standard for effective AFP detection. - The correct benchmark uses a 100,000 population denominator to ensure adequate detection of rare cases. *At least one case of non-polio AFP per year per 100000 population of under 5 years* - This option correctly uses the **100,000 population denominator** but incorrectly restricts the age group to **under 5 years**. - AFP surveillance aims to detect cases in individuals up to 15 years of age to effectively monitor for **poliovirus circulation**.

Question 1647: Which one of the following statements about influence of smoking on risk of Coronary Heart Disease is not true?

A. Influence of smoking is only additive to other risk factors for CHD (Correct Answer)
B. Influence of smoking is synergistic to other risk factors for CHD
C. Influence of smoking is independent of other risk factors for CHD
D. Influence of smoking is directly related to number of cigarettes smoked per day

Explanation: ***Influence of smoking is only additive to other risk factors for CHD*** - The effects of smoking on CHD risk are considered to be **synergistic**, meaning the combined effect of smoking and other risk factors is greater than the sum of their individual effects. - Therefore, stating it is *only* additive makes this statement incorrect. *Influence of smoking is synergistic to other risk factors for CHD* - Smoking interacts with other CHD risk factors (e.g., hypertension, hyperlipidemia) in a **multiplicative way**, significantly amplifying the overall risk for developing heart disease. - This synergistic interaction means that the presence of smoking greatly increases the impact of other risk factors. *Influence of smoking is independent of other risk factors for CHD* - Smoking is a **major independent risk factor** for Coronary Heart Disease, meaning it can cause CHD even in the absence of other risk factors. - It directly damages the endothelium, promotes thrombosis, and increases inflammation, contributing to atherosclerosis regardless of other conditions. *Influence of smoking is directly related to number of cigarettes smoked per day* - The risk of CHD is generally **dose-dependent** with smoking; the more cigarettes a person smokes, the higher their risk. - This direct relationship highlights that even light smoking carries a risk, and heavy smoking significantly escalates it.

Question 1648: Among various species of mosquitoes belonging to Anopheles genus, one that is highly anthropophilic and transmits even at low density is

A. Anopheles culicifacies
B. Anopheles stephensi
C. Anopheles fluviatilis (Correct Answer)
D. Anopheles sundaicus

Explanation: ***Anopheles fluviatilis*** - This species is known for being **highly anthropophilic** (prefers human blood) and having a high vectorial capacity, allowing it to transmit malaria effectively even at **low mosquito densities**. - Its efficient transmission at low densities makes it a significant vector, particularly in forest and foothill regions. *Anopheles culicifacies* - This is a major vector in rural India, particularly prevalent in **agricultural areas** and at higher densities. - While an important vector, it is generally associated with higher densities for efficient transmission compared to *An. fluviatilis*. *Anopheles stephensi* - This species is a primary vector in **urban and peri-urban areas**, adapted to breeding in domestic water containers. - While anthropophilic, its transmission efficiency at very low densities is not as pronounced as *An. fluviatilis* in its characteristic habitats. *Anopheles sundaicus* - This species is typically found in **coastal saline or brackish water** breeding sites in Southeast Asia. - While it is an important vector in those specific ecological niches, it doesn't possess the same level of efficient low-density transmission and broad anthropophilic behavior as *An. fluviatilis* across different settings.

Question 1649: There are 40 new cases of carcinoma of breast per 100,000 women/ year in country 'X' & 100 new cases / 100,000 women/ year in Country 'Y'. Based on this statistical data which of the following statement is true?

A. More women in Country 'Y' are smokers
B. Country 'X' has more number of younger women than country 'Y' (Correct Answer)
C. More preventive & screening measures like mammography are available in Country 'X'
D. More women in Country 'X' had breastfed their children

Explanation: ***Country 'X' has more number of younger women than country 'Y'*** - This statement implies that the age distribution of the population significantly impacts disease incidence rates, especially for diseases like breast carcinoma that increase with age. If Country 'X' has a younger population, its **age-adjusted incidence rate** might be similar to or even higher than Country 'Y's, despite the crude incidence being lower. - The presented data represents **crude incidence rates**. Without age-standardization, comparing crude incidence rates between populations with different age structures can be misleading. A lower crude incidence in Country 'X' could be due to a younger population, masking a potentially similar or higher age-specific risk. - This is the most likely explanation for the observed difference and demonstrates understanding of the importance of age-standardization in epidemiological comparisons. *More women in Country 'Y' are smokers* - While smoking is a risk factor for several cancers, its direct and strong association with **breast cancer incidence** is not as pronounced as with other cancers (e.g., lung cancer). The evidence linking smoking to breast cancer is weak and inconsistent. - Country 'Y' having more smokers does not adequately explain its higher breast cancer incidence compared to Country 'X' based solely on this limited data. *More preventive & screening measures like mammography are available in Country 'X'* - Effective **screening programs** like mammography typically **increase** detected incidence rates, not decrease them, due to earlier detection of previously undiagnosed cases (detection bias). - Better screening leads to higher reported incidence (at least initially), not lower incidence. Therefore, this option contradicts the observed lower incidence in Country 'X' and cannot explain the data. - Screening affects **detection rates and stage at diagnosis**, but does not reduce the actual occurrence of disease. *More women in Country 'X' had breastfed their children* - **Breastfeeding** is known to be a protective factor against breast cancer, potentially lowering a woman's lifetime risk. - While this could contribute to a lower incidence in Country 'X', this factor alone is unlikely to explain such a large disparity (2.5-fold difference) in crude incidence rates, especially when compared to the impact of population age structure, which is a much stronger determinant of crude incidence rates.

Question 1650: Incidence of TB in a community is measured by

A. Tuberculin test positive
B. Sputum smear positive (Correct Answer)
C. Mantoux test positive
D. Sputum culture

Explanation: ***Sputum smear positive*** - The **incidence of TB** in a community is best measured by the number of new **sputum smear-positive** cases, as these individuals are actively shedding bacilli and are infectious. - This method directly identifies individuals with **active disease** who are capable of transmitting the infection, thus reflecting new cases rather than past exposure. *Tuberculin test positive* - A **positive tuberculin test** (or TST) indicates exposure to TB bacilli and an immune response, but it does not differentiate between **latent TB infection (LTBI)** and active disease. - Many individuals with a positive test will never develop active TB, making it a poor measure of the *incidence of new active cases*. *Mantoux test positive* - The **Mantoux test** is another name for the **tuberculin skin test (TST)**, yielding the same limitations as "tuberculin test positive." - It primarily measures **delayed-type hypersensitivity** to tuberculin proteins, reflecting prior exposure rather than current, active, and transmissible disease. *Sputum culture* - While **sputum culture** is the gold standard for diagnosing active TB disease due to its high sensitivity, it is more expensive and time-consuming than sputum smear microscopy. - For measuring incidence at a community level, **sputum smear positivity** is often preferred for its practicality, speed, and ability to identify the most infectious cases promptly.

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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