Epidemiology — MCQs
On this page
What does the term 'proportional mortality rate' refer to?
Which vector is MOST commonly associated with transovarial transmission in diseases like Kyasanur Forest Disease and Crimean-Congo Hemorrhagic Fever?
Following are examples of human "dead end" diseases except -
Berksonian bias is a type of ?
Which disease is associated with a propagative cycle?
In the context of epidemiology, what is the denominator used for calculating incidence?
What is the term for the time between infection and maximum infectivity?
According to WHO guidelines, what prevalence of Bitot's spots indicates a public health problem?
Which study design is primarily used to understand the natural history of a disease?
Which of the following is considered the most basic measure of mortality?
Epidemiology Indian Medical PG Practice Questions and MCQs
Question 1791: What does the term 'proportional mortality rate' refer to?
- A. The total number of deaths in a given year
- B. The number of deaths in a specific month
- C. The total number of deaths regardless of cause
- D. The proportion of deaths due to a specific cause in relation to total deaths (Correct Answer)
Explanation: ***The proportion of deaths due to a specific cause in relation to total deaths*** - The **proportional mortality rate** calculates the fraction of all deaths in a population attributable to a particular cause. - This metric helps to understand the relative importance of specific diseases or conditions as causes of death within a given period. *The total number of deaths in a given year* - This option describes the **crude death count** or **absolute number of deaths**, not a proportional rate. - It does not provide information about the **distribution** or **proportion** of deaths due to specific causes. *The number of deaths in a specific month* - This refers to a **monthly death count**, which is a measure of absolute frequency over a shorter period. - It does not represent a **proportion** of specified deaths compared to total deaths. *The total number of deaths regardless of cause* - This is the **total mortality count** over a specified period, typically used to calculate the **crude mortality rate** when divided by the population size. - It does not differentiate deaths by **cause** or express them as a **proportion** of the total.
Question 1792: Which vector is MOST commonly associated with transovarial transmission in diseases like Kyasanur Forest Disease and Crimean-Congo Hemorrhagic Fever?
- A. Ticks (Correct Answer)
- B. Mosquitoes
- C. Fleas
- D. Mites
Explanation: ***Ticks*** - Ticks are the primary **vectors** for transmitting **Kyasanur Forest Disease** (KFD virus) and **Crimean-Congo Hemorrhagic Fever** (CCHF virus), both relevant to India. - **Transovarial transmission** is a key mechanism where pathogens are passed from an infected female tick to her offspring via eggs, perpetuating the disease cycle within tick populations. - KFD is endemic to **Karnataka** (Western Ghats), while CCHF has been reported from various parts of India including Gujarat, Rajasthan, and Uttar Pradesh. *Mosquitoes* - Mosquitoes are known vectors for diseases like **malaria**, **dengue fever**, and **chikungunya**, but not for KFD or CCHF. - They primarily transmit pathogens through **salivary injection** during blood feeding, not typically via transovarial transmission for these specific tick-borne illnesses. *Fleas* - Fleas are vectors for diseases such as the **plague** (Yersinia pestis) and **murine typhus** (Rickettsia typhi). - They do not transmit KFD or CCHF, and their mode of transmission is typically through flea bites rather than transovarial mechanisms for these conditions. *Mites* - Mites can cause various skin conditions (e.g., **scabies**) and transmit **scrub typhus** (Orientia tsutsugamushi), which is relevant in India. - However, they are not associated with the transmission of KFD or CCHF.
Question 1793: Following are examples of human "dead end" diseases except -
- A. Hydatid disease
- B. Japanese encephalitis
- C. Leishmaniasis
- D. Bubonic plague (Correct Answer)
Explanation: ***Bubonic plague (Plague)*** - The question refers to **plague in general**, which includes multiple clinical forms. - While **bubonic plague** (the most common form) is transmitted via **flea bites** from infected rodents and humans are typically dead-end hosts for this form, **pneumonic plague** (secondary complication or primary infection) allows **human-to-human transmission** via respiratory droplets. - This makes plague the **exception** among the listed diseases, as humans can serve as a source of infection to others in the pneumonic form, unlike true dead-end host situations. *Japanese encephalitis* - Humans are **dead-end hosts** for Japanese encephalitis virus. - Infected humans do not develop sufficient **viremia** to infect feeding mosquitoes. - The virus maintains its cycle between **Culex mosquitoes**, **pigs** (amplifying hosts), and **wading birds**, with humans being incidental hosts. *Hydatid disease* - Humans are **definitive dead-end hosts** for *Echinococcus granulosus* (causing cystic echinococcosis/hydatid disease). - The normal life cycle requires **definitive hosts** (dogs, canids) and **intermediate hosts** (sheep, cattle). - Humans develop **hydatid cysts** but cannot transmit the infection further as the parasite cannot complete its life cycle in humans. *Leishmaniasis* - In most forms of leishmaniasis, humans are considered **dead-end or accidental hosts**, particularly in **zoonotic cutaneous leishmaniasis** where animal reservoirs (rodents, dogs) maintain transmission. - However, in **anthroponotic visceral leishmaniasis** (*Leishmania donovani* in the Indian subcontinent), humans can serve as reservoir hosts. - For the purpose of this question, leishmaniasis is generally classified with dead-end diseases as the majority of leishmaniasis forms have zoonotic cycles where humans are incidental hosts with limited onward transmission.
Question 1794: Berksonian bias is a type of ?
- A. Selection bias (Correct Answer)
- B. Information bias
- C. Interviewer bias
- D. Recall bias
Explanation: ***Selection bias*** - **Berkson's bias** is a form of **selection bias** that arises in studies conducted using hospital data. - It occurs when the probability of admission to a hospital or inclusion in a study is conditional on both exposure and disease status, leading to a **flawed association** between them. *Interviewer bias* - **Interviewer bias** is a type of **information bias** where the interviewer's expectations or knowledge about the study or participants influence the way information is sought or recorded. - This typically affects the **data collection process** and not the selection of participants. *Information bias* - **Information bias** is a broad category of biases that arise from **systematic errors in measurement** or classification of exposure or disease. - While Berkson's bias can lead to misinformation, its root cause is in how subjects are selected, not how data on those subjects is collected after selection. *Recall bias* - **Recall bias** is a type of **information bias** where there are systematic differences in the way participants **recall past events or exposures**. - It is particularly common in **case-control studies** where individuals with a disease may remember exposures differently than healthy controls.
Question 1795: Which disease is associated with a propagative cycle?
- A. None of the options
- B. Plague
- C. Filaria (Correct Answer)
- D. Malaria
Explanation: ***Filaria*** - The **filarial worm** undergoes a **biological transmission cycle** in the mosquito vector where microfilariae develop through larval stages (L1 → L2 → L3) with multiplication. - This represents a **cyclopropagative cycle** (both development and multiplication occur in the vector). - In the context of this question and classical teaching, filaria is considered the standard example of biological transmission with vector multiplication. - The infective L3 larvae multiply from a single microfilaria, and multiple larvae can develop within one mosquito. *Plague* - **Plague** (*Yersinia pestis*) is transmitted by fleas through **mechanical transmission**. - Bacteria multiply in the flea's gut causing blockage (blocking transmission), but this is not considered a true biological cycle. - The pathogen does not undergo developmental stages in the vector. *Malaria* - **Malaria** (*Plasmodium* spp.) undergoes the **sporogonic cycle** in the mosquito, which is also a **cyclopropagative cycle**. - Gametocytes → ookinete → oocyst → sporozoites (development with multiplication). - While biologically similar to filaria, in classical epidemiology teaching, filaria is more commonly cited as the example for propagative transmission. *None of the options* - This option is incorrect as filaria demonstrates biological transmission with multiplication in the vector. - Both filaria and malaria technically undergo cyclopropagative cycles, but filaria is the conventional answer in medical education contexts.
Question 1796: In the context of epidemiology, what is the denominator used for calculating incidence?
- A. Mid year population
- B. Population at risk (Correct Answer)
- C. Total number of cases
- D. Total number of deaths
Explanation: ***Population at risk*** - Incidence measures the **rate of new cases** of a disease in a population over a specified period. - The denominator for calculating incidence must exclude individuals who are **already diseased** or are **immune** and thus not susceptible to developing the condition. - This is the **most accurate and theoretically correct** denominator as it represents only those who can actually develop the disease. *Mid year population* - While often used as a **practical approximation** in epidemiological calculations when the exact population at risk is difficult to determine. - However, it includes individuals who may not be at risk (e.g., already have the disease or are immune), making it **less precise** than using the actual susceptible population. - For the **theoretical definition** of incidence rate, population at risk is the correct denominator. *Total number of cases* - This value represents the **numerator** for incidence calculations, as it counts the number of new events or diseases occurring. - It cannot serve as the denominator, as the denominator must reflect the pool of individuals from which these **new cases arose**. *Total number of deaths* - This is a measure of **mortality**, not incidence, and is used to calculate death rates. - The denominator for mortality rates is typically the **population at risk of death**, not specifically the population at risk of developing a disease.
Question 1797: What is the term for the time between infection and maximum infectivity?
- A. Communicable period
- B. Generation time (Correct Answer)
- C. Incubation period
- D. Serial interval
Explanation: ***Generation time*** - This is the **time interval** between receipt of infection by a host and the moment of **maximum infectivity** of that same host. - It is a crucial parameter in epidemiology for understanding **disease transmission dynamics** and the speed at which an epidemic can spread. *Incubation period* - This refers to the time from **exposure to an infectious agent** until the **onset of symptoms**. - It does not directly account for the timing of viral shedding or peak infectivity. *Serial interval* - This is the time between **symptom onset in a primary case** and **symptom onset in a secondary case** it infects. - While related to transmission, it focuses on symptomatic presentation rather than peak infectivity. *Communicable period* - This is the time during which an infected individual is **capable of transmitting** the infectious agent to others. - It represents the entire duration of potential transmission, not specifically the peak infectivity.
Question 1798: According to WHO guidelines, what prevalence of Bitot's spots indicates a public health problem?
- A. > 1% prevalence
- B. > 2% prevalence
- C. None of the options
- D. ≥ 0.5% prevalence (Correct Answer)
Explanation: ***≥ 0.5% prevalence*** - According to **WHO guidelines**, a prevalence of Bitot's spots of **≥ 0.5%** (greater than or equal to 0.5%) in children aged 6-71 months indicates a **moderate public health problem** related to **vitamin A deficiency**. - This threshold is used for **programmatic decision-making** and intervention strategies to combat **xerophthalmia** (vitamin A deficiency eye disease). - At **≥ 1.0%** prevalence, it indicates a **severe public health problem**. *> 1% prevalence* - While ≥ 1% prevalence indicates a **severe public health problem**, the **initial WHO threshold** for identifying a public health problem due to **vitamin A deficiency** as indicated by Bitot's spots is **≥ 0.5%**. - This allows for **earlier public health action** before the situation becomes severe. *> 2% prevalence* - A prevalence of 2% implies a **critical vitamin A deficiency situation**, far exceeding the **WHO's diagnostic threshold** for initiating public health interventions. - Interventions would be critically urgent at this level, but the criteria for recognizing a problem are met at **≥ 0.5%**. *None of the options* - This option is incorrect because the **WHO has specific guidelines** for the prevalence of **Bitot's spots** that indicate a public health problem. - The correct threshold of **≥ 0.5%** is provided among the choices, which is the established criterion for a **moderate public health problem**.
Question 1799: Which study design is primarily used to understand the natural history of a disease?
- A. Cohort studies (Correct Answer)
- B. Cross-sectional studies
- C. Case-control studies
- D. Randomized controlled trials
Explanation: ***Cohort studies*** - **Cohort studies** follow a group of individuals over a period, allowing researchers to observe the incidence, progression, and outcomes of a disease naturally. - They are ideal for understanding the **natural history** of a disease, identifying risk factors, and assessing prognosis. - By following subjects from exposure to outcome, cohort studies reveal the temporal sequence and progression patterns of disease. *Cross-sectional studies* - **Cross-sectional studies** assess a population at a single point in time, providing a snapshot of disease prevalence and risk factor distribution. - They cannot establish temporal relationships or the natural progression of a disease because they lack follow-up over time. *Case-control studies* - **Case-control studies** compare individuals with a disease (cases) to individuals without the disease (controls) to identify past exposures or risk factors. - They are retrospective and focus on identifying potential causes of a disease *after* it has occurred, rather than observing its natural development. *Randomized controlled trials* - **Randomized controlled trials (RCTs)** are experimental studies designed to test the efficacy of interventions by randomly assigning participants to treatment or control groups. - They focus on evaluating therapeutic interventions rather than observing the natural, unmodified course of disease.
Question 1800: Which of the following is considered the most basic measure of mortality?
- A. Crude death rate (Correct Answer)
- B. Case fatality rate
- C. Proportional mortality rate
- D. Specific death rate
Explanation: ***Crude death rate*** - The **crude death rate** is the total number of deaths in a given period divided by the total population, making it the most basic and fundamental measure of mortality. - It provides an overall picture of mortality in a population without considering age, sex, or cause of death. *Case fatality rate* - The **case fatality rate** measures the proportion of individuals diagnosed with a specific disease who die from that disease. - It is specific to a particular condition and not a general measure of mortality for a whole population. *Proportional mortality rate* - The **proportional mortality rate** indicates the proportion of all deaths due to a specific cause. - It describes the relative importance of a specific cause of death but does not represent the actual risk of dying from that cause in the overall population. *Specific death rate* - A **specific death rate** refers to mortality rates calculated for specific population subgroups (e.g., age-specific, sex-specific, or cause-specific). - While more detailed, it is not the most basic measure as it involves stratification beyond the raw population count.
Practice by Chapter
Principles of Epidemiology
Practice Questions
Measures of Disease Frequency
Practice Questions
Epidemiological Study Designs
Practice Questions
Descriptive Epidemiology
Practice Questions
Analytical Epidemiology
Practice Questions
Experimental Epidemiology
Practice Questions
Screening for Disease
Practice Questions
Surveillance Systems
Practice Questions
Investigation of an Epidemic
Practice Questions
Association and Causation
Practice Questions
Modern Epidemiological Methods
Practice Questions
Critical Appraisal of Epidemiological Studies
Practice Questions
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free