Epidemiology Practice Questions

Q: Which of the following diseases has the largest submerged portion in the iceberg model of disease?

Influenza. **The Iceberg Model of Disease** represents the concept that for many diseases, only a small portion of cases (the "tip" above water) are clinically apparent and reported, while a much larger portion (the "submerged" part) consists of asymptomatic, subclinical, or undiagnosed cases. ***Influenza*** - Has the **largest submerged portion** among the given options, with **50-75% of infections being asymptomatic or mild** and going undiagnosed - High transmissibility and varied clinical presentation contribute to significant hidden burden - Only severe cases requiring hospitalization typically get reported, representing just the "tip of the iceberg" - Classic example of diseases with large subclinical-to-clinical ratio *Chickenpox* - Most cases are **clinically apparent** with characteristic vesicular rash - Asymptomatic infections are rare due to distinctive clinical features - High visibility of cases reduces the submerged portion significantly *Tetanus* - **Severe, acute neurological condition** with distinct clinical manifestations (trismus, risus sardonicus, opisthotonus) - Almost all cases are diagnosed due to dramatic presentation - Virtually no submerged portion - what exists clinically is recognized *Rabies* - **Nearly uniformly fatal** once symptoms appear, making all symptomatic cases clinically evident - No asymptomatic or mild phase after symptom onset - Minimal to no submerged portion in the iceberg model

Q: Which of the following is a true statement about screening tests for genetic diseases?

It defines risk of transmission of disease to the child. ***Correct: It defines risk of transmission of disease to the child*** - Genetic screening aims to identify individuals or couples at risk of passing on **heritable genetic conditions** to their offspring. - This information helps in **family planning** and provides prenatal diagnostic options if the risk is high. - This is the **primary purpose** of genetic screening programs. *Incorrect: Screening test has better accuracy than diagnostic test* - **Screening tests** are designed to be broad and detect potential risks, often with lower specificity and sensitivity than diagnostic tests. - **Diagnostic tests** are typically more accurate and definitive, confirming the presence or absence of a disease after a positive screening result. *Incorrect: It is always invasive* - Many genetic screening tests, such as **non-invasive prenatal screening (NIPS)** from maternal blood or carrier screening via saliva, are non-invasive or minimally invasive. - While some diagnostic tests like **amniocentesis** or **chorionic villus sampling** are invasive, screening itself is not universally so. *Incorrect: Screening requires genetic mapping* - **Genetic mapping** refers to determining the relative positions of genes on a chromosome, which is a research tool for understanding genome organization. - Genetic screening primarily involves testing for specific mutations or chromosomal abnormalities, not creating a comprehensive genetic map of an individual.

Q: Match the incubation periods of the following diseases: a. Syphilis b. SARS c. Hepatitis A d. Chickenpox Match with: 1. 10-21 days 2. 21 days (3 weeks) 3. 2-7 days 4. 15-50 days

a-2, b-3, c-4, d-1. ***a-2, b-3, c-4, d-1*** - This option correctly matches all incubation periods: **Syphilis (a) = 21 days (3 weeks)** - the average incubation for primary chancre appearance is 21 days (range 10-90 days). - **SARS (b) = 2-7 days** - the typical incubation period for SARS-CoV-1 is 2-10 days, with most cases manifesting within 2-7 days. - **Hepatitis A (c) = 15-50 days** - the standard incubation period averages 28-30 days (range 15-50 days). - **Chickenpox (d) = 10-21 days** - varicella has a well-established incubation of 10-21 days, typically 14-16 days. *a-3, b-4, c-2, d-1* - This incorrectly assigns **2-7 days to Syphilis**, which is far too short for the primary chancre to appear (actual: 21 days average). - **15-50 days for SARS** is excessively long; SARS manifests within 2-10 days. - **21 days for Hepatitis A** is at the lower end but not representative of the typical range (15-50 days). *a-2, b-3, c-1, d-4* - This incorrectly pairs **10-21 days with Hepatitis A**, which has a longer incubation (15-50 days). - **15-50 days for Chickenpox** is too long; varicella's incubation is 10-21 days. *a-4, b-3, c-1, d-2* - This incorrectly assigns **15-50 days to Syphilis** (actual: 21 days average) and **10-21 days to Hepatitis A** (actual: 15-50 days). - While these ranges have some overlap with actual values, they represent inversions of the correct assignments.

Q: Match the following: Column A: a. Syphilis b. Chickenpox c. COVID-19 d. Hepatitis A Column B: 1. 6 Days 2. 90 Days 3. 16 Days 4. 28 Days

a-2, b-3, c-1, d-4. ***a-2, b-3, c-1, d-4*** - **Syphilis**: 90 days represents the **maximum incubation period** for *Treponema pallidum* (range 10-90 days, typical 21 days). While not the most common presentation time, it remains medically accurate and is the only viable match among available options. - **Chickenpox**: 16 days falls within the typical incubation period for **varicella-zoster virus** (range 10-21 days, commonly 14-16 days). - **COVID-19**: 6 days is consistent with the **median incubation period** for SARS-CoV-2 (range 2-14 days, mean 5-6 days). - **Hepatitis A**: 28 days represents the **typical incubation period** for HAV (range 15-50 days, average 28-30 days). *a-3, b-4, c-2, d-1* - Incorrectly assigns **Syphilis** 16 days (below the 10-90 day range's typical value), **COVID-19** 90 days (far exceeding the 2-14 day range), and **Hepatitis A** only 6 days (well below the minimum 15-day period). *a-1, b-4, c-2, d-3* - Incorrectly matches **Syphilis** with 6 days (insufficient for *T. pallidum* to produce primary chancre), **Chickenpox** with 28 days (exceeds the typical VZV range), and **Hepatitis A** with 16 days (below typical range). *a-3, b-4, c-1, d-2* - Incorrectly assigns **Syphilis** 16 days, **Chickenpox** 28 days (exceeding typical range), and **Hepatitis A** 90 days (inconsistent with acute HAV infection pattern).

Q: Which of the following statements are true? 1. Due to increasing mammography there occurs over diagnosis of breast carcinoma 2. Colon cancer screening is done by digital rectal examination 3. Oral cancer screening is done by visual inspection 4. Cervix cancer screening is done by a pap smear

1,3,4. ***Correct: 1,3,4*** - **Statement 1 is TRUE**: Overdiagnosis is a well-documented consequence of increased mammography screening. It detects slow-growing tumors that might never have caused clinical symptoms or harm during a woman's lifetime, leading to unnecessary treatment and associated morbidities. - **Statement 3 is TRUE**: Oral cancer screening primarily involves thorough visual inspection by a healthcare professional to identify suspicious lesions, ulcers, or color changes in the oral cavity. - **Statement 4 is TRUE**: Cervical cancer screening is effectively done by Pap smear, which detects precancerous and cancerous cells. - **Statement 2 is FALSE**: Digital rectal examination is NOT the primary screening method for colon cancer. Standard screening methods include colonoscopy, fecal occult blood testing (FOBT), and fecal immunochemical test (FIT). *Incorrect: 1,2,3,4* - While statements 1, 3, and 4 are true, statement 2 is incorrect. Digital rectal examination is not a primary or definitive screening method for colon cancer—it only examines the rectum and misses most of the colon. *Incorrect: 4 only* - While cervical cancer screening by Pap smear is true, this option is incomplete as it misses other true statements (1 and 3) regarding mammography overdiagnosis and oral cancer screening. *Incorrect: 2,3,4* - This option incorrectly includes statement 2. Colon cancer screening is NOT done by digital rectal examination. Proper screening methods include colonoscopy, FOBT, FIT, and flexible sigmoidoscopy.

Q: A new drug has been introduced into the market which was found to decrease mortality but it does not cure the disease. Which of the following is a true statement regarding prevalence and incidence?

Increase in prevalence. ***Increase in prevalence*** - A drug that decreases mortality without curing the disease means people **live longer with the condition**, thus increasing the duration of disease - **Prevalence = Incidence × Duration**: Since duration increases while incidence remains constant, prevalence increases - More existing cases accumulate over time as fewer patients die from the disease *Decrease in incidence* - **Incidence** refers to the rate at which **new cases** develop in a population - This drug affects survival of existing cases, not the development of new cases - Since the drug neither prevents nor promotes new cases, **incidence remains unchanged** (not decreased) *Decrease in prevalence* - Prevalence would decrease if the drug **cured the disease** (removing people from the diseased pool) or if **mortality increased** - The scenario describes the opposite: decreased mortality without cure, which **increases** prevalence *Increase in incidence* - This would mean more new cases are developing over time - The drug affects **survival** of existing cases, not the **rate of new diagnoses** - Incidence remains unchanged, not increased

Q: Which of the following is not a part of case-control studies?

Follow up. ***Follow up*** - **Follow-up** of participants over time to observe disease incidence or outcomes is a characteristic of **cohort studies**, not case-control studies. - Case-control studies are typically **retrospective**, looking back in time after disease occurrence. *Strength of association* - Measuring the **strength of association** between an exposure and an outcome using metrics like the **odds ratio** is a primary objective of case-control studies. - This helps quantify the increased risk of disease attributable to a particular exposure. *Matching* - **Matching** is a technique frequently used in case-control studies to control for **confounding variables** by selecting controls who are similar to cases in terms of age, gender, or other relevant factors. - This helps ensure that any observed association is truly due to the exposure and not other differences between the groups. *Selection of study subjects* - The **selection of study subjects** is fundamental in case-control studies, involving the identification of individuals with the disease (**cases**) and a comparable group without the disease (**controls**). - Careful selection is crucial to minimize bias and ensure the validity of the study findings.

Q: Which indicator best measures the effectiveness of an STI control program's prevention efforts?

Incidence of new infections. ***Incidence of new infections*** - A decrease in the **incidence of new infections** directly reflects the success of **prevention strategies** in reducing overall disease transmission. - This indicator assesses the program's ability to prevent people from acquiring STIs, which is the ultimate goal of prevention efforts. *Number of screenings performed* - The number of screenings performed measures **program activity** and **reach**, but not necessarily the effectiveness of prevention. - While screening is crucial for early detection and treatment, it doesn't directly indicate a reduction in the **rate of new transmissions**. *Treatment completion rates* - Treatment completion rates are important for individual patient outcomes and reducing further transmission from **infected individuals**. - However, they primarily reflect the **effectiveness of treatment delivery** rather than the success of primary prevention among the uninfected population. *Number of cases treated* - The number of cases treated indicates the **burden of disease** and the program's response to it, but doesn't directly measure prevention success. - This metric can increase even if prevention efforts are failing, due to a rise in new infections or improved case finding.

Q: A well of contaminated water resulting in an epidemic of acute watery diarrhea is a typical example for:

Common source, single exposure epidemic. ***Common source, single exposure epidemic*** - A contaminated well is a **classic example of a point source (single exposure) epidemic**, as seen in John Snow's famous Broad Street pump cholera outbreak. - People who drink from the contaminated well are exposed to the pathogen at **roughly the same time or over a short period**. - The epidemic curve shows a **sharp rise in cases within one incubation period**, followed by a rapid decline, creating a characteristic **single peaked curve**. - Even though the well remains accessible, each individual's exposure is typically a **discrete event**, not continuous. *Common source, continuous exposure epidemic* - This occurs when the **source remains contaminated and people are repeatedly exposed over an extended period**, such as persistent sewage leakage into a water supply. - The epidemic curve would show a **prolonged plateau** with cases occurring continuously as long as the exposure continues. - Unlike a contaminated well (discrete exposures), continuous exposure involves **ongoing, repetitive contact** with the pathogen source. *Propagated epidemic* - Involves **person-to-person transmission** where the disease spreads through successive generations of cases. - The epidemic curve shows **multiple peaks** or waves as the infection passes from one individual to another. - Waterborne diarrhea from a well is **not transmitted person-to-person** but through a common environmental source. *Slow epidemic* - This is **not a standard epidemiological classification** based on exposure patterns. - While epidemics can vary in speed, this term doesn't describe the **transmission dynamics** relevant to classifying outbreak patterns.

Question 1

Which of the following diseases has the largest submerged portion in the iceberg model of disease?

Accepted Answer

Influenza

Answer

Chickenpox

Answer

Tetanus

Answer

Rabies

Question 2

Which of the following is a true statement about screening tests for genetic diseases?

Accepted Answer

It defines risk of transmission of disease to the child

Answer

Screening test has better accuracy than diagnostic test

Answer

It is always invasive

Answer

Screening requires genetic mapping

Question 3

Match the incubation periods of the following diseases:
a. Syphilis
b. SARS
c. Hepatitis A
d. Chickenpox

Match with:
1. 10-21 days
2. 21 days (3 weeks)
3. 2-7 days
4. 15-50 days

Accepted Answer

a-2, b-3, c-4, d-1

Answer

a-3, b-4, c-2, d-1

Answer

a-2, b-3, c-1, d-4

Answer

a-4, b-3, c-1, d-2

Question 4

Match the following:

Column A:
a. Syphilis
b. Chickenpox
c. COVID-19
d. Hepatitis A

Column B:
1. 6 Days
2. 90 Days
3. 16 Days
4. 28 Days

Accepted Answer

a-2, b-3, c-1, d-4

Answer

a-3, b-4, c-2, d-1

Answer

a-1, b-4, c-2, d-3

Answer

a-3, b-4, c-1, d-2

Question 5

Which of the following statements are true?

1. Due to increasing mammography there occurs over diagnosis of breast carcinoma
2. Colon cancer screening is done by digital rectal examination
3. Oral cancer screening is done by visual inspection
4. Cervix cancer screening is done by a pap smear

Accepted Answer

1,3,4

Answer

1,2,3,4

Answer

4 only

Answer

2,3,4

Question 6

A new drug has been introduced into the market which was found to decrease mortality but it does not cure the disease. Which of the following is a true statement regarding prevalence and incidence?

Accepted Answer

Increase in prevalence

Answer

Decrease in incidence

Answer

Decrease in prevalence

Answer

Increase in incidence

Question 7

Which of the following is not a part of case-control studies?

Accepted Answer

Follow up

Answer

Strength of association

Answer

Matching

Answer

Selection of study subjects

Question 8

Which indicator best measures the effectiveness of an STI control program's prevention efforts?

Accepted Answer

Incidence of new infections

Answer

Number of screenings performed

Answer

Treatment completion rates

Answer

Number of cases treated

Question 9

Why is sentinel surveillance preferred over passive surveillance in STI control programs?

Accepted Answer

Provides more detailed and accurate data from selected sites

Answer

Eliminates reporting bias

Answer

Covers larger population

Answer

Requires less resources

Question 10

A well of contaminated water resulting in an epidemic of acute watery diarrhea is a typical example for:

Accepted Answer

Common source, single exposure epidemic

Answer

Propagated epidemic

Answer

Slow epidemic

Answer

Common source, continuous exposure epidemic

Epidemiology — MCQs

Epidemiology — MCQs

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