Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1891: Commonest carcinoma in men in tropical countries is

A. Ca rectum
B. Ca testis
C. Ca bladder
D. Ca oral cavity (Correct Answer)

Explanation: ***Ca oral cavity*** - The high prevalence of **tobacco chewing** and **betel nut use** in many tropical countries significantly contributes to the high incidence of oral cavity cancer in men. - This habit is deeply ingrained in the **cultural practices** of these regions, leading to chronic irritation and carcinogenesis. *Ca rectum* - While colorectal cancer is common globally, it is generally **less prevalent** in tropical regions compared to oral cavity cancers attributed to specific lifestyle factors. - Its incidence is often linked to **Westernized diets** and sedentary lifestyles, which are not universally dominant in all tropical areas. *Ca testis* - Testicular cancer is more common in **younger men** in developed countries and is not typically the leading cancer in men across tropical regions. - It accounts for a **smaller proportion** of all male cancers globally compared to more prevalent cancers like oral cavity, lung, or prostate cancer. *Ca bladder* - Bladder cancer is often associated with **smoking** and occupational exposure to certain chemicals (e.g., dyes, rubber). - While present, it does not typically surpass the incidence of **oral cavity cancer** in tropical regions, where unique risk factors are highly prevalent.

Question 1892: Sandfly acts as a vector to all of the following diseases, except which of the following?

A. Kala-azar
B. Pappataci fever
C. Onchocerciasis (Correct Answer)
D. Leishmaniasis

Explanation: ***Onchocerciasis*** - **Onchocerciasis**, or river blindness, is transmitted by the **blackfly (Simulium species)**, not the sandfly. - The disease is caused by the filarial nematode *Onchocerca volvulus*, which is introduced into humans through the bite of an infected blackfly. *Pappataci fever* - **Pappataci fever**, also known as sandfly fever, is a viral disease transmitted by the bite of infected **sandflies (Phlebotomus species)**. - This disease is characterized by a sudden onset of fever, headache, and muscle pain. *Kala-azar* - **Kala-azar**, or visceral leishmaniasis, is a severe form of **leishmaniasis** transmitted by the bite of an infected female **sandfly (Phlebotomus species)**. - It is caused by intracellular parasites of the genus *Leishmania* and affects internal organs. *Leishmaniasis* - **Leishmaniasis** in its various forms (cutaneous, mucocutaneous, visceral) is transmitted by the bite of an infected female **sandfly**. - The sandfly acts as the definitive host and vector for the *Leishmania* parasites.

Question 1893: Which of the following statements about carriers of infectious diseases is true?

A. Carriers can show clinical symptoms of infection.
B. Carriers serve as a source of infection. (Correct Answer)
C. Carriers are more infectious than symptomatic cases.
D. Carriers are less dangerous than symptomatic cases.

Explanation: **_Carriers serve as a source of infection._** - A **carrier** is an individual who harbors an infectious agent without showing apparent clinical signs of the disease but can transmit it to others. - Their ability to transmit the pathogen makes them an important **source of infection** within a population. *Carriers can show clinical symptoms of infection.* - By definition, carriers do not exhibit **clinical symptoms** of the disease, although they may be infected. - If symptoms were present, the individual would be considered a **symptomatic case**, not a carrier. *Carriers are more infectious than symptomatic cases.* - The infectiousness of a carrier varies depending on the specific pathogen and host factors, but they are generally considered **less infectious** than symptomatic cases who are actively shedding high loads of pathogens. - **Symptomatic individuals** often shed pathogens more robustly due to active disease processes, leading to higher transmission rates. *Carriers are less dangerous than symptomatic cases.* - While carriers may show no symptoms and often shed fewer pathogens than symptomatic cases, they can be particularly **dangerous** because they can transmit the disease unknowingly and without protective measures. - Their **undetected transmission** contributes significantly to the spread of infectious diseases, especially in the early stages of an outbreak.

Question 1894: Which of the following is a distinguishing feature of Aedes mosquitoes compared to Anopheles mosquitoes?

A. Pupa has broad siphon
B. Wings unspotted (Correct Answer)
C. Pupa has a narrow siphon
D. Eggs are oval shaped

Explanation: ***Wings unspotted*** - **Aedes mosquitoes have unspotted wings**, which is a key distinguishing feature for adult identification. - *Anopheles* mosquitoes characteristically have **spotted wings** with patches of dark and pale scales, making this a reliable diagnostic criterion. - This is one of the most practical features for field identification of adult mosquitoes. *Pupa has a narrow siphon* - This is **incorrect** - *Aedes* pupae actually have a **broad and short respiratory siphon (trumpet)**. - *Anopheles* pupae have a **narrow and long siphon**, which is the opposite of what this option states. - Pupal characteristics are useful but require microscopic examination. *Pupa has broad siphon* - While *Aedes* pupae do have a **broader siphon** compared to *Anopheles*, this is less commonly used for routine identification. - The broad siphon refers to the respiratory trumpet structure at the cephalothorax. - However, **wing spotting pattern** remains the preferred adult identification method. *Eggs are oval shaped* - *Aedes* eggs are **oval/elongated and laid singly**, often on moist surfaces above the waterline. - *Anopheles* eggs are also **boat-shaped with lateral floats** and laid singly on the water surface. - Both genera have oval-shaped eggs, making this a less reliable distinguishing feature alone.

Question 1895: Which measure is most appropriate for assessing the infectivity of an organism?

A. Prevalence rate
B. Case fatality rate
C. Secondary attack rate (Correct Answer)
D. Incidence rate

Explanation: ***Secondary attack rate*** - This measure directly quantifies the **proportion of susceptible contacts** who develop the disease after exposure to a primary case, making it ideal for assessing **infectivity**. - A higher secondary attack rate indicates a more **highly transmissible** organism. *Prevalence rate* - This measures the **total number of existing cases** in a population at a specific time or over a period, reflecting the overall burden of disease. - It does not specifically indicate how easily an organism spreads from one person to another. *Case fatality rate* - This represents the **proportion of individuals diagnosed with a disease** who ultimately die from that disease. - It measures the **severity or virulence** of an infection, not its infectivity. *Incidence rate* - This measures the **rate at which new cases of a disease occur** in a population over a specified period. - While it reflects disease occurrence, it doesn't specifically assess the likelihood of transmission from an infected individual to their contacts.

Question 1896: Which of the following is a disadvantage of non-randomized trials?

A. Random assignment of subjects
B. The experiment can serve as its own control or can utilize a natural control
C. Several trials may be needed before evaluation is considered conclusive.
D. Degree of comparability is low (Correct Answer)

Explanation: ***Degree of comparability is low*** - Non-randomized trials have a **lower degree of comparability** between intervention and control groups because subjects are not randomly assigned, making it more difficult to attribute observed differences solely to the intervention. - This lack of comparability increases the risk of **confounding variables** influencing the results, as baseline characteristics of the groups may differ significantly. *Random assignment of subjects* - This is a *feature of randomized controlled trials (RCTs)*, not a disadvantage of non-randomized trials. RCTs use random assignment to create comparable groups. - In non-randomized trials, **random assignment is absent**, which is precisely why comparability can be low. *The experiment can serve as its own control or can utilize a natural control* - This describes a potential **advantage or characteristic of certain non-randomized designs**, like before-and-after studies or natural experiments. - While it can be useful in some contexts, it does not mitigate the fundamental issue of **low comparability** in non-randomized designs when comparing different groups. *Several trials may be needed before evaluation is considered conclusive.* - This statement applies broadly to many types of research, including some randomized trials, and indicates the need for **replication and robust evidence**. - While non-randomized trials might indeed require more supportive evidence due to their inherent limitations, this is a general research principle and not a unique disadvantage stemming from non-randomization itself, compared to the direct impact on comparability.

Question 1897: Repetition of a study in a given group is known as:

A. Cohort study
B. Cross-sectional study
C. Panel study (Correct Answer)
D. Repeated measures design (statistical)

Explanation: ***Panel study*** - A **panel study** is the epidemiological term for a longitudinal study design where the **same group of individuals is studied repeatedly** over time. - This directly answers the question: "repetition of a study in a given group" is known as a **panel study**. - The same panel (group) of subjects is examined or surveyed at multiple time points, allowing researchers to track changes within individuals over time. - Common in epidemiological research, social sciences, and health surveys (e.g., National Family Health Survey panels). *Repeated measures design (statistical)* - This term refers to a **statistical analysis technique** rather than a study design or research methodology. - While it involves analyzing data with multiple measurements from the same subjects, it is not what "repetition of a study in a given group" is called in epidemiological terminology. - It describes the statistical approach used to analyze such data, not the study design itself. *Cohort study* - A **cohort study** follows a group over time to assess the **incidence of disease or outcomes** and identify risk factors. - The focus is on comparing exposed vs. unexposed groups or following a cohort to observe new outcomes, not specifically on "repeating a study" in the same group. - While longitudinal, the term doesn't specifically denote repetition of measurements in the same individuals. *Cross-sectional study* - A **cross-sectional study** collects data at a **single point in time** to assess prevalence. - It provides a snapshot and involves **no repetition** over time, making it incorrect for this question.

Question 1898: In which months does the maximum spread of malaria typically occur in many endemic regions of India?

A. March-April
B. September - October (Correct Answer)
C. January-February
D. April-May

Explanation: ***September-October*** - The **peak transmission** season for **malaria** in many endemic regions of India occurs during the **post-monsoon** months. - This period provides optimal conditions for **mosquito breeding** due to accumulated water collections, moderate temperatures, and suitable humidity levels after the monsoon rains. - **Post-monsoon months** allow for maturation of mosquito populations that bred during monsoon, leading to maximum vector density and malaria transmission. *April-May* - These **pre-monsoon** months may show increased transmission in some regions, but this is **not the universal peak period** across India. - The preceding dry season usually means **fewer breeding sites** compared to post-monsoon period. - Temperatures are rising but **water collections are limited** before monsoon onset. *January-February* - These months typically represent the **winter season** in most parts of India where malaria is endemic. - **Lower temperatures** and reduced humidity are generally unfavorable for the survival of the *Anopheles* mosquito and the development of the *Plasmodium* parasite within the mosquito. - This represents the **lowest transmission period** in most endemic areas. *March-April* - While malaria transmission may begin to increase in these months, it generally **peaks later** after monsoon rains create abundant breeding sites. - The dry season conditions still prevail, limiting **vector breeding opportunities** compared to post-monsoon months.

Question 1899: In a cohort study conducted with 100 individuals in each group (exposed and non-exposed), out of those exposed to the risk factor, 10 are diseased, and out of those not exposed to the risk factor, only 5 are diseased. What is the relative risk?

A. 2 (Correct Answer)
B. 1.5
C. 0.75
D. 1

Explanation: ***Correct Option: 2*** - The **incidence in the exposed group** is 10/100 = 0.1. - The **incidence in the non-exposed group** is 5/100 = 0.05. - **Relative risk (RR)** is calculated as the ratio of the incidence in the exposed group to the incidence in the non-exposed group: 0.1 / 0.05 = 2. - This indicates that the **exposed group has twice the risk** of developing the disease compared to the non-exposed group. *Incorrect Option: 1.5* - This value would be obtained if the ratio of incidences was 0.075 / 0.05 or 0.1/0.066, which is not consistent with the given data. - An RR of 1.5 indicates a **lesser strength of association** than what is observed in this study. *Incorrect Option: 0.75* - This value would result if the incidence in the exposed group was *lower* than in the non-exposed group (e.g., 0.05 / 0.066), suggesting a **protective effect**. - An RR < 1 implies that exposure is protective rather than a risk factor, which contradicts the given data. *Incorrect Option: 1* - A **relative risk of 1** indicates there is no difference in the risk of disease between the exposed and non-exposed groups. - This would mean the incidence rate in both groups is identical (e.g., 0.1 / 0.1 = 1), which contradicts the provided data where exposed group has higher incidence.

Question 1900: Which of the following statements about the Urban Malaria Scheme is incorrect?

A. Utilization of anti-larva measures
B. Introduction of active surveillance
C. It is done in town/city with minimum 50,000 population (Correct Answer)
D. Slide positivity rate more than 10%

Explanation: ***It is done in town/city with minimum 50,000 population*** - This statement is **INCORRECT** because it misrepresents the eligibility criteria for the Urban Malaria Scheme. - The actual criterion is not based solely on a minimum population threshold; rather, the scheme is implemented in **towns and cities classified as urban areas** as per Census of India definitions, which may vary. - While many urban centers targeted have populations around or exceeding 50,000, the program focuses on **malaria endemicity and urban characteristics** rather than a fixed population cutoff. *Utilization of anti-larva measures* - This is a **CORRECT** statement about the Urban Malaria Scheme. - Anti-larval measures are a cornerstone of the program, including **source reduction, larvicides, and biological control** of mosquito breeding sites. - Urban environments have specific breeding sites (construction sites, overhead tanks, etc.) that require targeted anti-larval interventions. *Introduction of active surveillance* - This is a **CORRECT** statement about the Urban Malaria Scheme. - **Active case detection** through fever surveys and surveillance is a key component for early identification and treatment of malaria cases. - Active surveillance helps prevent outbreaks in densely populated urban areas. *Slide positivity rate more than 10%* - This is a **CORRECT** statement about the Urban Malaria Scheme. - Areas with **Slide Positivity Rate (SPR) ≥ 10%** are prioritized for intensive interventions under the scheme. - High SPR indicates active transmission and helps identify high-burden urban pockets requiring focused control measures.

Practice by Chapter

Principles of Epidemiology

Practice Questions

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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