Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1651: Which of the following is transmitted by mites:

A. Endemic typhus
B. Scrub typhus (Correct Answer)
C. Trench fever
D. Epidemic typhus

Explanation: **Scrub typhus** - This disease is caused by the bacterium *Orientia tsutsugamushi* and is transmitted to humans through the bite of infected **larval mites** (chiggers). - The mites are found in rural areas, particularly in parts of Asia, and their bite often leaves a characteristic **eschar** at the inoculation site. *Endemic typhus* - Also known as murine typhus, this condition is caused by *Rickettsia typhi* and is transmitted by the **rat flea**, not mites. - It is typically associated with rodent populations. *Trench fever* - This disease is caused by *Bartonella quintana* and is transmitted by the human **body louse**, not mites. - It was historically prevalent during wartime due to crowded, unsanitary conditions. *Epidemic typhus* - Caused by *Rickettsia prowazekii*, this form of typhus is transmitted by the human **body louse**, not mites. - It is often associated with outbreaks in areas with poor hygiene and crowded living conditions.

Question 1652: The screening method of choice in area where the prevalence of leprosy is 1/1000 is -

A. Group survey
B. Any of the above
C. Mass survey
D. Contact survey (Correct Answer)

Explanation: ***Contact survey*** - At a prevalence of **1/1000 (0.1%)**, leprosy is considered to have **low prevalence** in the population. - In low-prevalence settings, **contact survey** is the most efficient and cost-effective screening method, focusing on individuals who have been in close contact with known leprosy cases. - This targeted approach maximizes case detection yield while minimizing resources spent on screening low-risk populations. - Contact surveys are particularly important for leprosy due to its person-to-person transmission pattern and the high risk among household and close contacts. *Mass survey* - **Mass survey** (screening the entire population) is indicated when prevalence is **high (>10/1000)**, making population-wide screening cost-effective. - At 1/1000 prevalence, mass survey would be inefficient as it would screen 1000 people to find approximately 1 case, wasting resources. - Mass surveys are resource-intensive and only justified when disease burden is substantial across the general population. *Group survey* - **Group survey** targets specific high-risk groups (e.g., occupational groups, institutional settings) and is useful for **medium prevalence (1-10/1000)** settings. - While more focused than mass survey, it's still broader than needed at 1/1000 prevalence where contact tracing provides better yield. - Group surveys are appropriate when certain subpopulations have elevated risk but general population risk remains moderate. *Any of the above* - This is incorrect because the choice of screening method is **specifically determined by disease prevalence** and epidemiological principles. - At 1/1000 prevalence, **contact survey** is the evidence-based method of choice, not any arbitrary method. - Epidemiological practice requires matching the screening strategy to the prevalence level for optimal resource utilization.

Question 1653: WHO surveillance is done in all EXCEPT

A. Common cold (Correct Answer)
B. Cholera
C. Malaria
D. Polio

Explanation: ***Common cold*** - The **common cold** is a ubiquitous and generally self-limiting viral infection that does not meet the criteria for routine **WHO surveillance**, which typically focuses on diseases with significant public health impact, epidemic potential, or those targeted for elimination/eradication. - Due to its high incidence and low severity, surveillance resources are prioritized for more impactful diseases. *Cholera* - **Cholera** is a severe diarrheal disease with the potential for rapid spread and high mortality, especially in areas with poor sanitation, making it a critical disease for **WHO surveillance** to prevent and control outbreaks. - The WHO monitors cholera epidemiology, supports early warning systems, and coordinates response efforts globally. *Malaria* - **Malaria** is a life-threatening parasitic disease that affects millions annually, particularly in tropical and subtropical regions. It is a major focus of **WHO surveillance** efforts aimed at reducing morbidity and mortality and ultimately achieving elimination. - Surveillance helps track disease burden, monitor drug resistance, and evaluate the effectiveness of control interventions. *Polio* - **Polio** is a highly infectious viral disease that can cause irreversible paralysis and is the target of a global eradication initiative led by the WHO, making its surveillance absolutely critical. - **WHO surveillance** for polio aims to detect every case of paralysis to ensure rapid response and track progress towards total eradication.

Question 1654: Which of the following is not spread by fomites?

A. Diarrhea
B. Typhoid
C. Hepatitis A
D. AIDS (Correct Answer)

Explanation: ***AIDS*** - **AIDS (Acquired Immunodeficiency Syndrome)** is caused by the **Human Immunodeficiency Virus (HIV)**, which is primarily transmitted through direct contact with infected bodily fluids such as blood, semen, pre-ejaculate, vaginal fluids, and breast milk. - HIV is a fragile virus that cannot survive for long periods outside the human body and is not transmitted via inanimate objects or surfaces (fomites). *Diarrhea* - Many causes of **diarrhea**, particularly those due to **bacterial (e.g., Shigella, E. coli)** or **viral (e.g., Rotavirus, Norovirus)** infections, can be spread via fomites contaminated with fecal matter. - Poor hand hygiene after using the toilet can lead to contamination of surfaces, which are then touched by others, facilitating transmission. *Typhoid* - **Typhoid fever**, caused by **Salmonella Typhi**, is a classic example of a **fecal-oral transmitted disease**. - Food or water contaminated by an infected person's feces can lead to transmission, and contaminated surfaces or objects can serve as fomites. *Hepatitis A* - **Hepatitis A virus (HAV)** is primarily transmitted through the **fecal-oral route**, meaning it can easily spread through contaminated food, water, or objects. - Surfaces infected with HAV from contaminated hands can act as fomites, contributing to outbreaks.

Question 1655: Hill's criteria of causal association are all Except

A. Coherence
B. Consistency
C. Specificity of association
D. Sensitivity (Correct Answer)

Explanation: ***Sensitivity*** - **Sensitivity** is a measure of a **screening or diagnostic test's ability** to correctly identify true positives. It is not part of Hill's criteria for assessing causality. - Hill's criteria focus on establishing a causal link between an exposure and an outcome, not on the performance of a diagnostic test. *Coherence* - **Coherence** refers to the requirement that a causal explanation should not contradict generally accepted **facts of natural history** and **biology**. - It suggests that the causal relationship should make sense within known scientific principles. *Consistency* - **Consistency** means that similar results have been observed in **different studies** or settings, increasing the likelihood of a causal relationship. - Repeated observations of the association under various conditions strengthen the evidence for causality. *Specificity of association* - **Specificity of association** suggests that a single exposure leads to a **single disease** and not multiple diseases, and a single disease is caused by a single exposure. - While considered a criterion, it is often seen as a **weaker criterion** because many exposures can cause multiple outcomes, and many diseases have multiple causes.

Question 1656: Which of the following is not true about propagated epidemics?

A. Sharp rise and decrease sharply (Correct Answer)
B. Person to person transmission
C. Herd immunity present
D. Multiple waves of epidemic

Explanation: ***Sharp rise and decrease sharply*** - Propagated epidemics typically exhibit a **slow initial rise**, followed by a **gradual increase** in cases, and do not usually decrease sharply. - The onset and decline are **less abrupt** than common-source epidemics due to the time required for serial infections. *Person to person transmission* - A defining characteristic of propagated epidemics is the **transmission of disease agents directly** from one infected individual to another. - This mode of transmission leads to a **sequential spread** through the population, creating multiple generations of cases. *Herd immunity present* - As more individuals become immune through vaccination or natural infection, the **spread of the disease slows down**, a phenomenon known as herd immunity. - In a propagated epidemic, a sufficiently high level of **herd immunity can eventually halt** the transmission chains. *Multiple waves of epidemic* - Propagated epidemics often present with **multiple peaks or waves** as the disease spreads through different susceptible groups over time. - This occurs as new cohorts of susceptible individuals are exposed or as **immunity wanes**, leading to a resurgence of cases.

Question 1657: Most effective way of preventing hospital infection is:

A. Fumigation
B. Sterilization
C. Hand washing (Correct Answer)
D. Early diagnosis and treatment

Explanation: ***Hand washing*** - **Hand hygiene** is the single most important and effective measure for **preventing nosocomial infections** and the transmission of multidrug-resistant organisms. - It physically removes transient microorganisms and reduces the resident flora on hands, thereby **breaking the chain of infection**. - Recommended by **WHO** and **CDC** as the cornerstone of infection prevention in healthcare settings. *Fumigation* - **Fumigation** is a process involving the use of gaseous disinfectants to kill pests or microbes, primarily for **terminal disinfection of rooms** or large spaces. - While it can reduce microbial load on surfaces, it is **not used routinely** for preventing day-to-day transmission of pathogens from person to person. - Not practical or effective for continuous infection control. *Sterilization* - **Sterilization** is a process that destroys all forms of microbial life, including spores, primarily applied to **medical instruments** and surgical equipment. - While critical for preventing infection during invasive procedures, it is **not a direct method** for preventing general person-to-person transmission within a hospital environment. - Cannot be applied to hands or routine patient care activities. *Early diagnosis and treatment* - **Early diagnosis and treatment** are crucial for managing existing infections in patients, which can help prevent their spread within the hospital. - However, these measures primarily address **patient care** rather than directly interrupting the *transmission* of pathogens from healthcare workers to patients or between patients. - This is a **secondary prevention** measure, not primary prevention of transmission.

Question 1658: Measure of communicability of a disease -

A. Sullivan index
B. Incubation period
C. Secondary attack rate (Correct Answer)
D. Case fatality rate

Explanation: ***Secondary attack rate*** - This measures the **frequency of new cases** of a disease among contacts of known cases within a short period, reflecting how easily it spreads. - It specifically quantifies the **probability of infection** among susceptible individuals after exposure to a primary case. *Sullivan index* - The Sullivan index is a measure of **health expectancy**, specifically the number of years of life free of disability. - It is used in public health to assess the overall health status of a population, not disease communicability. *Incubation period* - The incubation period is the **time interval** between exposure to an infectious agent and the onset of clinical symptoms. - While important for understanding disease progression and isolation protocols, it does not directly measure the ease of transmission or communicability itself. *Case fatality rate* - The case fatality rate (CFR) indicates the **proportion of deaths** among individuals diagnosed with a specific disease. - It measures the **severity** of a disease, not how easily it spreads from person to person.

Question 1659: True regarding Japanese encephalitis is except -

A. The iceberg phenomenon is observed.
B. Human-to-human transmission is not reported.
C. Mortality is 80-90%. (Correct Answer)
D. Culicine mosquitoes are zoophilic.

Explanation: ***Mortality is 80-90%.*** - The **mortality rate** for Japanese encephalitis is generally reported between **20-30%** among symptomatic cases, particularly in children. - A mortality rate of 80-90% is excessively high and **inaccurate** for Japanese encephalitis. *The iceberg phenomenon is observed.* - The **iceberg phenomenon** is characteristic of Japanese encephalitis, meaning that for every symptomatic case, there are many **asymptomatic infections** that go undetected. - Only a small proportion of infected individuals develop severe neurological disease, while the majority remain subclinical. *Human-to-human transmission is not reported.* - Japanese encephalitis is a **vector-borne disease** transmitted primarily by mosquitoes; it is **not transmitted directly** from person to person. - The virus circulates between mosquitoes, amplifying hosts (like pigs), and humans are typically dead-end hosts. *Culicine mosquitoes are zoophilic.* - **Culicine mosquitoes**, particularly *Culex tritaeniorhynchus*, are the primary vectors and are indeed **zoophilic**, meaning they prefer to feed on animals (like pigs and wading birds). - This zoophilic nature contributes to the amplification cycle of the virus in animal reservoirs before humans are incidentally bitten.

Question 1660: Healthy carriers are not seen in

A. Vibrio cholerae
B. Salmonella typhi
C. Measles virus (Correct Answer)
D. Corynebacterium diphtheriae

Explanation: ***Measles virus*** - Measles infection does not typically lead to a **chronic carrier state**; individuals either recover completely or succumb to the disease. - The virus is eliminated from the host after the acute phase, and **lifelong immunity** usually develops. *Vibrio cholerae* - Individuals can be **asymptomatic carriers** and shed the bacteria in their feces, contributing to the spread of cholera. - This carrier state can persist for weeks after recovery from acute infection. *Salmonella typhi* - **Chronic carriers** of *Salmonella typhi* can excrete the bacteria for years, often harboring it in the **gallbladder**. - These carriers are a significant source of infection for others, famously exemplified by "Typhoid Mary." *Corynebacterium diphtheriae* - Asymptomatic carriers can harbor *C. diphtheriae* in their **nasopharynx** and transmit the bacteria to susceptible individuals. - This carrier state can persist for extended periods, even in the absence of overt disease symptoms.

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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