Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1781: What is the descending order of cancer incidence among males globally for the following cancer types?

A. Pharynx > lung > oral > esophagus
B. Esophagus > oral > stomach > lung
C. Oral > lung > pharynx > esophagus
D. Lung > oral > pharynx > esophagus (Correct Answer)

Explanation: ***Oral > lung > pharynx > esophagus*** - This sequence accurately reflects the **prevalence rates** of cancers among males [1], with **oral cancer** notably high in certain regions. - **Lung cancer** follows as the second most prevalent due to risk factors like **smoking** and air pollution [1]. *Lung > oral > pharynx > esophagus* - While lung cancer is indeed common, this order is incorrect as it **underestimates oral cancer**, which is highly prevalent in specific populations. - The ranking does not reflect **regional variations** in cancer prevalence, particularly in areas with high oral cancer rates. *Esophagus > oral > stomach > lung* - This order inaccurately places **esophageal cancer** above oral cancer, failing to account for the high prevalence of oral cancers in many regions. - The statement does not align with common epidemiological data that shows **lung cancer preeminence** in general male populations [1]. *Pharynx > lung > oral > esophagus* - This incorrect sequence ranks pharyngeal cancer too high, ignoring the more **established prevalence** of oral and lung cancers. - The order does not reflect the understanding that **lung cancer** remains one of the leading cancers among men [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 284-286.

Question 1782: A patient involved in a road traffic accident has undergone amputation of the right leg. What is the most appropriate term to describe this condition?

A. A pathological condition affecting the body.
B. A limitation in performing daily activities.
C. A social disadvantage resulting from an impairment.
D. A loss of body structure or function. (Correct Answer)

Explanation: ***A loss of body structure or function*** (CORRECT - Definition of Impairment) - The amputation of a leg directly involves the **loss of a body structure** (the leg itself) and subsequently a loss of its function (e.g., ambulation). - This definition aligns with the WHO International Classification of Functioning, Disability and Health (ICF) framework's definition of **impairment**, which is a problem in body function or structure such as significant deviation or loss. - Amputation is a classic example of an impairment. *A pathological condition affecting the body* - While amputation results from a pathological process (trauma), the term **"pathological condition"** generally refers to the disease or injury itself (e.g., gangrene requiring amputation, or the trauma from the accident), not the direct consequence of the removal of a body part. - Amputation is a **treatment** or outcome of a pathological condition, rather than the condition itself in this context. *A limitation in performing daily activities* - This describes **"activity limitation"** (formerly termed "disability" in the old ICIDH classification), which is the consequence of an impairment at the level of the individual's activities. - While an amputee will experience limitations in daily activities, this term describes the functional impact, not the direct physical state of having lost a limb. *A social disadvantage resulting from an impairment* - This refers to **"participation restriction"** (formerly termed "handicap" in the old ICIDH classification), which is the disadvantage experienced by an individual as a result of an impairment or disability, acting as a barrier to fulfilling a social role. - This is a social and environmental concept, distinct from the direct physical loss of a body part.

Question 1783: Which of the following is the primary component of the AFP (Acute Flaccid Paralysis) case definition used in polio surveillance?

A. All of the above
B. Stool specimen positive for poliovirus
C. Onset of acute flaccid paralysis (Correct Answer)
D. Presence of residual paralysis after 60 days

Explanation: ***Onset of acute flaccid paralysis*** - The primary component of the **AFP case definition** for polio surveillance is the acute onset of **flaccid paralysis** in a child under 15 years, or paralytic illness in a person of any age when polio is suspected. - This definition is crucial for identifying all potential cases of polio, regardless of the cause, to ensure thorough investigation and prevent outbreaks. *Stool specimen positive for poliovirus* - A positive stool specimen for poliovirus is a **laboratory confirmation** of polio infection, but it is not the primary component of the initial case definition. - The AFP case definition aims for **high sensitivity** to capture all possible cases for investigation, even before laboratory results are available. *Presence of residual paralysis after 60 days* - Residual paralysis after 60 days is an important indicator for **classifying a confirmed polio case** and understanding the long-term impact. - However, it is a **follow-up criterion** used after the initial detection of AFP, not the primary component that triggers the initial surveillance. *All of the above* - While laboratory confirmation and residual paralysis provide further information about a case, the **initial identification relies specifically on the clinical presentation** of acute flaccid paralysis. - The broad clinical definition ensures that no potential polio case is missed, initiating an immediate public health response.

Question 1784: Randomization is done to reduce?

A. Recall bias
B. Selection bias (Correct Answer)
C. Berksonian bias
D. Reporting bias

Explanation: ***Selection bias*** - **Randomization** ensures that each participant has an equal chance of being assigned to any study group, which helps to distribute both known and unknown confounding factors evenly. - This process minimizes **selection bias** by promoting comparability between groups, making it more likely that any observed differences are due to the intervention rather than pre-existing differences. *Recall bias* - **Recall bias** occurs when there are systematic differences in the way participants remember or report past exposures or events, often seen in retrospective studies. - While randomization helps control for confounding, it does not directly prevent participants from inaccurately recalling information. *Berksonian bias* - **Berksonian bias** is a form of selection bias where the probability of being admitted to a hospital (or selected into a study) is affected by the presence of a co-morbidity, leading to a distorted association between diseases. - Randomization aims to balance characteristics *within* the study groups once participants are recruited, but it doesn't address biases related to the initial selection into the study population from a larger source. *Reporting bias* - **Reporting bias** refers to selective revealing or suppression of information, either by study participants (e.g., social desirability bias) or by researchers (e.g., only reporting positive findings). - Randomization helps ensure internal validity by creating comparable groups, but it does not prevent individuals from selectively reporting outcomes or experiences.

Question 1785: Which of the following statements about incidence is false?

A. Does not include unit of time (Correct Answer)
B. It is a rate
C. Numerator includes new cases
D. Denominator includes population at risk

Explanation: ***Does not include unit of time*** - This statement is false because **incidence** is defined as the number of **new cases** of a disease over a specific period of time in a population at risk. - Therefore, it inherently includes a **unit of time** (e.g., per year, per month), making this option incorrect as a characteristic of incidence. *It is a rate* - **Incidence is a rate** because it quantifies the speed at which new cases of a disease occur within a population. - It expresses the number of new events (cases) per unit of population at risk over a specified time period. *Numerator includes new cases* - The **numerator of incidence** specifically counts the number of **new cases** of a disease that develop during a defined observation period. - This distinguishes it from prevalence, which includes all existing cases. *Denominator includes population at risk* - The **denominator for incidence** comprises the **population at risk** of developing the disease during the observation period. - Individuals who already have the disease or are immune are typically excluded from the denominator.

Question 1786: Transovarian transmission is seen in-

A. Malaria
B. Filaria
C. Rickettsial diseases (Correct Answer)
D. None of the options

Explanation: ***Rickettsial diseases*** - **Transovarian transmission** is a key mechanism for the maintenance and spread of **rickettsiae** in arthropod vectors. The bacteria can pass from an infected female arthropod (like a tick or mite) to her offspring via the eggs. - This ensures that the next generation of vectors is already infected and can transmit the disease, even without needing to acquire the pathogen from an infected vertebrate host. *Malaria* - Malaria is transmitted via the bite of an infected **Anopheles mosquito**, which acquires parasites from an infected human. - **Transovarian transmission** does not occur in malaria; mosquitoes are not born with the ability to transmit the parasite. *Filaria* - Filariasis is spread by various **mosquito vectors** (e.g., *Culex*, *Anopheles*, *Aedes*) or **black flies**, which acquire microfilariae from an infected host during a blood meal. - The parasite undergoes development within the insect, but **transovarian transmission** to the insect's offspring does not occur. *None of the options* - This option is incorrect because **rickettsial diseases** do exhibit transovarian transmission, making it a valid answer. - The phenomenon of passing pathogens directly from a female parent to her offspring via the egg is a specific mechanism seen in certain vector-borne diseases.

Question 1787: When is screening for breast cancer recommended?

A. When the disease has a low case fatality rate
B. When diagnostic tools are available
C. When no effective treatment is available
D. When early diagnosis can change the disease course due to effective treatment (Correct Answer)

Explanation: ***When early diagnosis can change the disease course due to effective treatment*** - **Screening** for cancer, like breast cancer, is most beneficial when early detection allows for interventions that effectively alter the disease's natural progression, leading to better outcomes. - The availability of **effective treatments** is a cornerstone for recommending screening programs, as finding a disease early without the means to treat it effectively offers little patient benefit. *When the disease has a low case fatality rate* - Diseases with a **low case fatality rate** are generally less urgent candidates for widespread screening, as the potential benefit of early detection is diminished if the disease is not often fatal. - Screening is more commonly applied to diseases with **significant morbidity and mortality**, where early intervention can make a substantial difference. *When diagnostic tools are available* - While the availability of **diagnostic tools** is a prerequisite for screening, it is not the sole determinant for recommending a screening program. - The diagnostic tools must also be **accurate, safe, and cost-effective**, and their use must lead to improved patient outcomes through early intervention. *When no effective treatment is available* - If **no effective treatment** is available, screening for a disease can cause more harm than good due to the psychological burden of diagnosis without the possibility of intervention. - In such cases, screening is generally not recommended, as it does not improve **patient prognosis** or quality of life.

Question 1788: Who is often referred to as the 'Father of Modern Epidemiology'?

A. Edwin Chadwick
B. Lemuel Shattuck
C. Robert Koch
D. John Snow (Correct Answer)

Explanation: ***John Snow*** - **John Snow** is widely recognized as the **"Father of Modern Epidemiology"** for his groundbreaking work in identifying the source of the 1854 **Broad Street cholera outbreak** in London. - He used epidemiological methods like **dot maps** and **cohort analysis** to trace the outbreak to a contaminated water pump, establishing the **waterborne transmission** of cholera. *Edwin Chadwick* - Edwin Chadwick was a key figure in the **public health reform movement** in 19th-century Britain, advocating for improved sanitation and living conditions. - While significant, his work was focused on **social reform and sanitation infrastructure** rather than developing the scientific methods of epidemiology. *Lemuel Shattuck* - Lemuel Shattuck was an American statistician and public health reformer known for his 1850 report on the sanitary conditions of Massachusetts. - His work was influential in establishing a **public health infrastructure** in the United States, but he is not credited with founding modern epidemiological methods. *Robert Koch* - Robert Koch was a German physician and microbiologist renowned for his contributions to the field of **bacteriology**, particularly for identifying the specific causative agents of diseases like **anthrax, tuberculosis, and cholera**. - While his work was crucial for understanding infectious diseases, his primary focus was on **microbiology and germ theory**, not the ecological and population-level study of disease distribution that characterizes epidemiology.

Question 1789: 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 1790: 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.

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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