Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1621: Hard ticks transmit

A. Tick typhus
B. Viral encephalitis
C. KFD
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - Hard ticks are vectors for diverse pathogens, including bacteria causing **tick typhus**, viruses leading to **viral encephalitis**, and the **Kyasanur Forest Disease (KFD)** virus. - Their biting mechanism and feeding habits facilitate the transmission of multiple diseases simultaneously or sequentially. *Tick typhus* - **Tick typhus** (Rocky Mountain spotted fever, Mediterranean spotted fever) is caused by **Rickettsia rickettsii** and other Rickettsia species, which are transmitted by hard ticks. - Symptoms include fever, headache, and a characteristic rash, which are spread by hard ticks like *Dermacentor* and *Rhipicephalus* species. *Viral encephalitis* - Several **encephalitic viruses**, such as **Tick-borne encephalitis virus (TBEV)**, are transmitted by hard ticks (e.g., *Ixodes* species), leading to neurological symptoms. - The virus primarily affects the central nervous system, causing inflammation of the brain. *KFD* - **Kyasanur Forest Disease (KFD)** is a **viral hemorrhagic fever** endemic to India, specifically transmitted by hard ticks (e.g., *Haemaphysalis spinigera*). - It causes high fever, headache, muscle pain, and can lead to severe gastrointestinal bleeding and neurological manifestations.

Question 1622: Amplifier host in Japanese encephalitis is:

A. Monkey
B. Pigs (Correct Answer)
C. Dogs
D. Horse

Explanation: ***Pigs*** - **Pigs** are the primary **amplifier hosts** for Japanese encephalitis virus, meaning they develop high viremia and can efficiently transmit the virus to mosquitoes. - This high viral load in pigs plays a crucial role in maintaining and intensifying the **transmission cycle** of the disease. *Monkey* - While **monkeys** can be infected with Japanese encephalitis, they are generally considered **dead-end hosts** or have a minor role in amplification. - They do not typically develop a high enough viremia to efficiently transmit the virus back to mosquitoes. *Dogs* - **Dogs** are not known to be significant **reservoir hosts** or **amplifier hosts** for Japanese encephalitis. - They are generally considered refractory to infection or develop only mild, subclinical disease. *Horse* - **Horses** can be infected with Japanese encephalitis and may develop neurological symptoms, including fatal encephalitis. - However, they are considered **dead-end hosts** as they do not develop sufficient viremia to transmit the virus back to mosquitoes.

Question 1623: Most sensitive indicator of recent transmission of malaria in a community is:-

A. Infant parasite rate (Correct Answer)
B. Annual parasite rate
C. Mosquito rate
D. Spleen rate

Explanation: ***Infant parasite rate*** - This measures the proportion of infants (typically under 1 year old) in a community who have **malaria parasites** in their blood. - Since infants have limited mobility and are less likely to have been exposed to malaria in distant areas, their infection status is a direct reflection of **recent local transmission**. *Annual parasite rate* - This indicates the average number of positive malaria blood slides per 100 population per year, reflecting the **overall burden of malaria** in a community over a longer period. - While it's an important epidemiological indicator, it doesn't specifically target **recent transmission** as effectively as the infant parasite rate. *Mosquito rate* - This refers to the density or prevalence of **malaria-carrying mosquitoes** (e.g., Anopheles mosquitoes) in a given area. - While essential for understanding transmission potential, it does not directly measure human infection and therefore is not a direct indicator of **recent human transmission**. *Spleen rate* - This measures the proportion of children (typically 2-9 years old) with an **enlarged spleen**, which is a common but non-specific sign of chronic or repeated malaria infections. - It reflects past exposure and chronic malaria in the community and is not a sensitive indicator of **recent transmission**.

Question 1624: Disease elimination is helped by-

A. Contact tracing
B. Herd immunity (Correct Answer)
C. Quarantine
D. Isolation

Explanation: ***Herd immunity*** - **Herd immunity** occurs when a large percentage of a population becomes immune to an infectious disease, providing indirect protection to those who are not immune. This significantly reduces the transmission chain and can stop the spread of a disease, aiding in its elimination. - When the proportion of immune individuals reaches a certain threshold, the **reproductive number (R0)** of the pathogen drops below 1, meaning each infected person transmits the disease to fewer than one other person on average, leading to a decline and eventual elimination of the disease. - **Examples:** Smallpox elimination was achieved through vaccination creating herd immunity; polio elimination efforts rely on achieving high immunization coverage. *Contact tracing* - **Contact tracing** involves identifying and monitoring people who may have been exposed to an infected person to prevent further transmission. - While it is an essential **disease control measure** during outbreaks, it addresses individual chains of transmission rather than creating population-level immunity necessary for elimination. *Quarantine* - **Quarantine** involves separating and restricting the movement of apparently healthy people who may have been exposed to a contagious disease to see if they become sick. - While essential for **preventing disease spread** during an outbreak, it is a control measure and does not directly eliminate a disease from a population. *Isolation* - **Isolation** is the separation of sick people with a contagious disease from people who are not sick to prevent the spread of illness. - It is a crucial measure for **disease control** and management of active cases, but it does not achieve population-level immunity or directly lead to disease elimination.

Question 1625: Typhoid Mary is known in history to cause more than 1300 cases in her lifetime. This is an example of which of the following epidemic?

A. Propagated epidemic
B. Common source continuous or repeated exposure epidemic (Correct Answer)
C. Common source single exposure epidemic
D. Long term or secular trend epidemic

Explanation: ***Common source continuous or repeated exposure epidemic*** - **Typhoid Mary** was a **chronic asymptomatic carrier** of *Salmonella Typhi*, meaning she continuously or repeatedly shed the bacteria. - As a cook, she **repeatedly exposed others to the pathogen** through contaminated food over many years, leading to numerous outbreaks. *Propagated epidemic* - A propagated epidemic occurs through **person-to-person transmission**, where the infection spreads sequentially over time, each infected person becoming a source for subsequent cases. - While Typhoid Mary eventually led to multiple cases, her primary role was as a continuous source rather than initiating a person-to-person chain where every new case infected another. *Common source single exposure epidemic* - This type of epidemic involves a **single, brief exposure** to the common source, such as a contaminated meal served once. - Typhoid Mary's numerous cases spanned years, indicating **multiple exposures** rather than a single event. *Long term or secular trend epidemic* - A **secular trend** refers to changes in disease frequency over **long periods**, often decades or centuries, reflecting gradual shifts in risk factors or environmental conditions. - Typhoid Mary's impact was a series of acute outbreaks over a shorter, defined period, not a gradual long-term trend.

Question 1626: What is the overall most common cancer in the world?

A. Thyroid carcinoma
B. Lung cancer
C. Breast cancer (Correct Answer)
D. Colon cancer

Explanation: ***Breast cancer*** - **Breast cancer** is the most common cancer globally by incidence, with approximately **2.3 million new cases** diagnosed annually (GLOBOCAN 2020). - It surpassed lung cancer in 2020 to become the leading cancer worldwide, affecting both women (predominantly) and men. - High incidence is seen particularly in developed countries, though rates are rising globally. *Lung cancer* - **Lung cancer** is the **second most common cancer** globally by incidence but remains the **leading cause of cancer deaths** worldwide. - While it has high mortality due to late diagnosis and aggressive nature, its overall incidence is slightly lower than breast cancer. - Strongly associated with smoking and environmental pollutants. *Thyroid carcinoma* - **Thyroid carcinoma** has increasing incidence but is not among the top most common cancers globally. - It has excellent prognosis with early detection and treatment, predominantly affecting women but also occurring in men. - The increase in incidence is partly due to improved detection methods. *Colon cancer* - **Colon cancer** (colorectal cancer) is the third most common cancer globally but does not surpass breast cancer in overall incidence. - Its occurrence varies geographically and is strongly linked to lifestyle factors including diet, obesity, and physical inactivity.

Question 1627: Epidemic marker of TB?

A. Tuberculin test positivity rate
B. Sputum AFB positivity rate (Correct Answer)
C. Chest x-ray positivity rate
D. None of the options

Explanation: ***Sputum AFB positivity rate*** - The **sputum acid-fast bacilli (AFB) positivity rate** directly indicates the number of individuals actively shedding viable *Mycobacterium tuberculosis* in their respiratory secretions. - This metric reflects the **infectious pool** within a community, making it a robust marker for assessing ongoing transmission and the epidemic status of tuberculosis. *Tuberculin test positivity rate* - The **tuberculin skin test (TST)** measures exposure to TB and latent infection, not active, infectious disease. - A high positivity rate indicates a high prevalence of **latent TB infection**, but doesn't differentiate between old exposure, cleared infection, or active disease, nor does it directly measure transmissibility. *Chest x-ray positivity rate* - **Chest X-rays** can identify pulmonary abnormalities consistent with TB, including active disease. - However, CXR findings are **non-specific** for TB and can be suggestive of previous infection or other lung conditions, making it less precise than sputum AFB for defining an active epidemic. *None of the options* - This option is incorrect because the **sputum AFB positivity rate** is a well-established and direct indicator of active TB disease transmission and epidemic activity.

Question 1628: What is the best indicator for a potential explosiveness of plague outbreak?

A. Specific percentage of fleas
B. Total flea index
C. Cheopis index (Correct Answer)
D. Burrow index

Explanation: **Cheopis index** - The **Cheopis index** (or *Xenopsylla cheopis* index) is the average number of *X. cheopis* fleas per rat. - A Cheopis index of **1 or greater** indicates a high risk of plague transmission and potential for an explosive outbreak. *Specific percentage of fleas* - While the presence of specific flea species is important, a **specific percentage of fleas** alone doesn't directly quantify the risk of an outbreak in the same way as a density index. - This metric might be used in conjunction with other indices but is not the primary indicator of explosiveness. *Total flea index* - The **total flea index** refers to the average number of all flea species per host. - It does not differentiate between vector species (like *X. cheopis*) and non-vector species, making it less specific for assessing plague risk. *Burrow index* - The **burrow index** refers to the number of active rodent burrows per unit area. - While it reflects rodent population density, it does not directly measure the **flea burden** on those rodents, which is crucial for assessing plague transmission risk.

Question 1629: Transition from increased prevalence of infectious and communicable diseases to man-made diseases is known as

A. Demographic transition
B. Paradoxical transition
C. Epidemiological transition (Correct Answer)
D. Reversal of transition

Explanation: ***Epidemiological transition*** - This term describes the shift in **disease patterns** observed in many populations, moving from a predominance of **infectious and communicable diseases** to an increased prevalence of **chronic, non-communicable diseases** (often described as "man-made" due to their association with lifestyle and environmental factors). - This transition is typically linked to advancements in **public health**, sanitation, medicine, and changes in socioeconomic status. *Demographic transition* - This concept describes the historical shift from high **birth rates** and **death rates** to low birth rates and death rates as a country develops from a pre-industrial to an industrialized economic system. - While related to disease patterns through changes in population structure, it directly focuses on **population growth** and age distribution, not specific disease prevalence. *Paradoxical transition* - This is not a recognized or standard public health or demographic term for the described phenomenon. - The term "paradoxical" would imply a contradictory or unexpected outcome, which is not the primary descriptor for the shift in disease patterns. *Reversal of transition* - This term would imply a return to previous patterns, such as an increase in **infectious diseases** after a period of decline. - While possible in specific contexts (e.g., due to antibiotic resistance or weakened public health systems), it does not describe the initial shift from infectious to man-made diseases.

Question 1630: Epidemic resulting from person to person transmission is known as:

A. Point source epidemic.
B. Common source epidemic.
C. Propagated epidemic. (Correct Answer)
D. Mixed epidemic.

Explanation: ***Propagated epidemic*** - This type of epidemic is characterized by **person-to-person transmission**, resulting in a pattern of increasing cases over time until a significant portion of the susceptible population is infected or interventions are effective. - The epidemic curve typically shows **multiple waves** or peaks, reflecting successive generations of infection. - Classic examples include **measles, chickenpox, and influenza** outbreaks. *Point source epidemic* - A point source epidemic occurs when people are exposed to the **same source** over a **brief, limited period**. - The epidemic curve typically shows a **sharp upward slope** and a gradual downward slope, with cases clustering around a single incubation period. - Does not involve person-to-person transmission. *Common source epidemic* - This type of epidemic results from exposure to a **common noxious influence**, such as contaminated food or water, affecting multiple individuals. - Common source epidemics can be further classified as **point source** or **continuous/intermittent source** depending on the duration of exposure. - Does not primarily involve person-to-person transmission. *Mixed epidemic* - A mixed epidemic starts as a **common source outbreak** but is followed by **secondary person-to-person transmission**. - Shows characteristics of both common source and propagated epidemics in its epidemic curve. - Not the primary term for person-to-person transmission epidemics.

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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