Epidemiology Practice Questions

Q: Other than cataract, which one among the following is the highest prevalent cause of blindness in the world ?

Glaucoma. ***Glaucoma*** - **Glaucoma** is the **second leading cause of blindness globally** after cataract, accounting for approximately 12-15% of all cases of blindness worldwide. - It is a group of eye conditions that damage the optic nerve, often due to elevated intraocular pressure, leading to **irreversible vision loss**. - Unlike cataract, glaucoma-induced blindness is **irreversible**, making it a major public health concern. - The prevalence is particularly high in older populations and varies by type (primary open-angle, angle-closure, etc.). *Corneal opacity* - **Corneal opacity** is an important cause of blindness, especially in developing countries, resulting from infections (corneal ulcers), trauma, vitamin A deficiency, and trachoma sequelae. - While significant, it accounts for approximately 4-5% of global blindness, ranking **below glaucoma** in overall prevalence. - Prevention through nutrition programs and timely treatment of infections has reduced its burden. *Trachoma* - **Trachoma**, caused by *Chlamydia trachomatis*, is a chronic keratoconjunctivitis and was historically a leading infectious cause of blindness. - Due to WHO's GET2020 (Global Elimination of Trachoma by 2020) initiative and SAFE strategy (Surgery, Antibiotics, Facial cleanliness, Environmental improvement), its prevalence has **declined significantly**. - It now accounts for less than 3% of global blindness. *Diabetic retinopathy* - **Diabetic retinopathy** is a growing cause of blindness, particularly in developed countries and among working-age adults, due to the diabetes epidemic. - It accounts for approximately 5% of global blindness. - While its prevalence is increasing, it remains **below glaucoma** as a cause of global blindness.

Q: Which one of the following is a correct combination regarding Indian population?

Blood group O 40%; Rh negative 7%. ***Blood group O 40%; Rh negative 7%*** - In the Indian population, **Blood group O** is indeed the most common, accounting for approximately **30-40%** of the population. - The prevalence of **Rh-negative** individuals in India is relatively low, typically around **5-7%**, making this combination accurate. *Blood group AB 20%; Rh negative 15%* - **Blood group AB** is the least common blood group, typically less than **10%** in the Indian population, making 20% an overestimation. - **Rh negative** prevalence of 15% is significantly higher than the reported figures for India, which are usually around 5-7%. *Blood group A 40%; Rh positive 80%* - While **Blood group A** is common, 40% might be slightly higher than some estimates, which often place it closer to 20-25%. - **Rh positive** prevalence in India is much higher than 80%, typically around **93-95%**, making 80% an underestimation. *Blood group B 33%; Rh positive 99%* - **Blood group B** is also very common in India, often around 30-35%, so 33% is a reasonable estimate. - However, **Rh positive** prevalence of 99% is an overestimation; the actual prevalence is closer to **93-95%**.

Q: In a community with one lakh population, 20,000 slides were examined in a particular year. Out of these 100 were positive for malarial parasite. What is the Annual Parasite Incidence (API) in this community ?

1. ***Correct Answer: 1*** The **Annual Parasite Incidence (API)** is a key epidemiological indicator for malaria surveillance, defined as the number of **confirmed positive malaria cases per 1,000 population per year**. **Formula:** API = (Number of positive cases / Total population) × 1,000 **Calculation:** - Population = 1,00,000 (one lakh) - Positive cases = 100 - API = (100 / 1,00,000) × 1,000 = **1** The number of slides examined (20,000) is relevant for calculating the **Slide Positivity Rate (SPR)** but not directly used in the API calculation. *Incorrect: 2* - This would be correct if there were 200 positive cases in the same population - Represents double the actual API *Incorrect: 0.5* - This would be correct if there were only 50 positive cases in the population - Represents half the actual API *Incorrect: 5* - This would result from incorrectly using the number of slides examined (20,000) as the denominator instead of the total population (1,00,000) - Confuses SPR calculation methodology with API calculation

Q: Berksonian bias is a selection bias which occurs in

Hospital based studies. ***Hospital based studies*** - **Berksonian bias** is a type of **selection bias** that occurs when the study population is drawn from a hospital or clinical setting. - This can lead to an artificially inflated or deflated association between risk factors and diseases, as hospital patients often have multiple health conditions or risk factors not representative of the general population. *Natural exposure studies* - These studies observe populations exposed to a factor naturally, without intervention, and are less prone to selection bias related to hospital admission. - While other biases can occur, **Berksonian bias** specifically relates to admission criteria for healthcare facilities. *Community based studies* - **Community-based studies** aim to recruit participants from the general population, making them less susceptible to **Berksonian bias** compared to hospital-based studies. - They strive for a more representative sample, reducing the selection pressures seen in clinical settings. *Laboratory based studies* - **Laboratory studies** typically use controlled environments and experimental designs, often involving cell cultures or animal models. - They are generally not subject to **Berksonian bias**, which is specific to human population studies drawing from clinical settings.

Q: Failure rate of contraceptive method is determined by:

Pearl index. ***Pearl index*** - The **Pearl index** is a common measure of the effectiveness of a birth control method, indicating the number of accidental pregnancies per 100 women-years of exposure. - A lower Pearl index signifies a **more effective contraceptive method**, meaning fewer pregnancies occur during its use. *Total fertility rate* - The **total fertility rate (TFR)** represents the average number of children born to a woman over her lifetime if she were to experience current age-specific fertility rates. - It reflects overall **population reproduction trends** and not the failure rate of a specific contraceptive method. *Age specific fertility rate* - The **age-specific fertility rate (ASFR)** measures the number of births to women in a particular age group per 1,000 women in that age group per year. - This rate provides insights into **fertility patterns across different age brackets** but does not quantify contraceptive effectiveness. *Half life index* - The term **"half-life index"** is not a standard epidemiological or public health measure for contraceptive failure rates. - Half-life usually refers to the **time it takes for a substance to decrease by half** (e.g., drug elimination) or for a radioactive isotope to decay.

Q: The useful fertility indicator where birth registration statistics do not exist or are inadequate is :

Child-woman ratio. ***Child-woman ratio*** - The **child-woman ratio** is a common **fertility indicator** used in areas where reliable birth registration data is unavailable. - It calculates the number of **children under 5 years old per 1000 women of childbearing age** (typically 15-49 years), providing an estimate of recent fertility. *Abortion rate* - The **abortion rate** measures the number of abortions per 1,000 women of reproductive age. - While it reflects a component of reproductive behavior, it does not directly measure live births or general fertility and relies on accurate abortion statistics which may also be inadequate. *Net reproduction rate* - The **net reproduction rate (NRR)** is a sophisticated measure that indicates the average number of daughters a woman will have if she survives to the end of her reproductive years, taking into account mortality. - This indicator requires **detailed birth and death statistics by age**, which are precisely what are lacking when birth registration is inadequate. *Male-female ratio* - The **male-female ratio**, or sex ratio, compares the number of males to females in a population. - This ratio is a demographic indicator used to understand population structure but **does not directly measure fertility**.

Q: A village has a total of 100 under-five children. The coverage with measles vaccine in these age groups is 60%. Following the occurrence of a measles case in a child after a visit outside, twenty six children developed measles later. The secondary attack rate of measles is :

66.6%. ***66.6%*** - The **secondary attack rate** is calculated as (number of secondary cases / number of susceptible contacts exposed to the primary case) × 100. - Total children = 100, with 60% vaccinated (60 children), leaving **40 susceptible children**. - The primary case (one child from the village who visited outside) is part of these 40 susceptible children. - After the primary case occurs, the **remaining susceptible contacts** = 40 - 1 = **39 children**. - Number of secondary cases = 26, so secondary attack rate = (26/39) × 100 = **66.67% ≈ 66.6%**. *65.0%* - This option incorrectly uses all 40 susceptible children as the denominator (26/40 × 100 = 65%). - The error lies in **not excluding the primary case** from the denominator when calculating the secondary attack rate. - The primary case cannot be counted among those "at risk" of secondary infection since they already have the disease. *26.0%* - This represents the **overall attack rate** calculated as (26/100) × 100, using the total population as the denominator. - It fails to account for **vaccination status** and does not represent the secondary attack rate among susceptible contacts. - This is epidemiologically incorrect for measuring disease transmission among susceptibles. *16.6%* - This option appears to use an incorrect denominator, possibly 26/156 or another erroneous calculation. - It does not reflect any standard epidemiological rate calculation for this scenario. - The value is too low to represent the true risk among susceptible contacts.

Q: Apgar score is used in:

Newborn assessment. ***Newborn assessment*** - The **Apgar score** is a standardized clinical assessment tool used to evaluate the **physical condition of newborn infants** immediately after birth. - Developed by Dr. Virginia Apgar in 1952, it assesses five parameters at **1 minute and 5 minutes** after delivery (extended to 10, 15, and 20 minutes if needed). - The five components assessed are: - **A**ppearance (skin color): 0-2 points - **P**ulse (heart rate): 0-2 points - **G**rimace (reflex irritability): 0-2 points - **A**ctivity (muscle tone): 0-2 points - **R**espiration (breathing effort): 0-2 points - **Total score ranges from 0-10**, with scores of 7-10 considered normal, 4-6 indicating moderate distress, and 0-3 indicating severe distress requiring immediate resuscitation. - It helps **identify neonates requiring immediate medical intervention** and provides a standardized method for documenting the newborn's transition to extrauterine life. *Maternal health assessment* - Maternal health is assessed using different tools such as **antenatal risk scoring systems**, blood pressure monitoring, and laboratory investigations. - The Apgar score is specifically designed for **neonates, not mothers**. *Nutritional status evaluation* - Nutritional status is assessed using anthropometric measurements like **weight-for-height, BMI, MUAC** (mid-upper arm circumference), and biochemical markers. - The Apgar score does not evaluate nutritional parameters. *Infectious disease severity grading* - Infectious disease severity uses specific scoring systems like **APACHE II, SOFA score, or disease-specific criteria** (e.g., WHO classification for dengue severity). - The Apgar score is a **neonatal assessment tool**, not used for infectious disease evaluation.

Q: Serial interval is the gap between :

Primary and secondary case. ***Primary and secondary case*** - The **serial interval** is defined as the time between the onset of symptoms in a **primary case** and the onset of symptoms in a **secondary case** infected by the primary case. - It is a crucial epidemiological parameter used to estimate the **reproduction number (R)** of infectious diseases. *Index and primary case* - The **index case** is the first case identified in an outbreak, while the **primary case** is the actual first case to get the disease. These two might not always be the same. - The serial interval specifically links the source of transmission (primary case) to the recipient (secondary case) based on symptom onset. *Introduction of infection and development of maximum infectivity* - This describes the **incubation period** or a phase within it, not the serial interval. - The serial interval measures the time between symptomatic onsets in a transmission chain. *Transmission of infection from patient to another susceptible host* - This describes the event of **actual transmission**, but the serial interval is the time duration between the manifestation of symptoms in the two individuals involved in this transmission. - It focuses on the time between **symptom onset**, not the time of transmission itself.

Q: In a village of 5,000 population, 50 persons suffered from cholera and 10 persons died. What will be the case fatality ratio?

20.0%. ***20.0%*** - The **case fatality ratio (CFR)** is calculated as the number of deaths from a specific disease divided by the number of confirmed cases of that disease, multiplied by 100. - In this scenario, 10 deaths / 50 cases = 0.2, and 0.2 * 100 = **20.0%**. *0.2%* - This value is likely derived from an incorrect calculation, possibly dividing the number of deaths by the total population, which would represent a **mortality rate**, not a case fatality ratio. - The **case fatality ratio** specifically relates deaths to the number of *cases*, not the entire population. *5.0%* - This calculation might be a misinterpretation of the formula or an application of the wrong denominator. - The correct denominator for **case fatality ratio** is the number of **cases**, not the total population or a subset of it unrelated to the disease. *1.0%* - This percentage would result from a different set of numbers for deaths and cases, or an error in calculation. - The **case fatality ratio** is focused on the severity of the disease among those who *contract* it, not the prevalence in the general population.

Question 1

Other than cataract, which one among the following is the highest prevalent cause of blindness in the world ?

Accepted Answer

Glaucoma

Answer

Trachoma

Answer

Corneal opacity

Answer

Diabetic retinopathy

Question 2

Which one of the following is a correct combination regarding Indian population?

Accepted Answer

Blood group O 40%; Rh negative 7%

Answer

Blood group AB 20%; Rh negative 15%

Answer

Blood group A 40%; Rh positive 80%

Answer

Blood group B 33%; Rh positive 99%

Question 3

In a community with one lakh population, 20,000 slides were examined in a particular year. Out of these 100 were positive for malarial parasite. What is the Annual Parasite Incidence (API) in this community ?

Accepted Answer

1

Answer

2

Answer

0.5

Answer

5

Question 4

Berksonian bias is a selection bias which occurs in

Accepted Answer

Hospital based studies

Answer

Natural exposure studies

Answer

Community based studies

Answer

Laboratory based studies

Question 5

Failure rate of contraceptive method is determined by:

Accepted Answer

Pearl index

Answer

Total fertility rate

Answer

Age specific fertility rate

Answer

Half life index

Question 6

The useful fertility indicator where birth registration statistics do not exist or are inadequate is :

Accepted Answer

Child-woman ratio

Answer

Abortion rate

Answer

Net reproduction rate

Answer

Male-female ratio

Question 7

A village has a total of 100 under-five children. The coverage with measles vaccine in these age groups is 60%. Following the occurrence of a measles case in a child after a visit outside, twenty six children developed measles later. The secondary attack rate of measles is :

Accepted Answer

66.6%

Answer

26.0%

Answer

65.0%

Answer

16.6%

Question 8

Apgar score is used in:

Accepted Answer

Newborn assessment

Answer

Maternal health assessment

Answer

Nutritional status evaluation

Answer

Infectious disease severity grading

Question 9

Serial interval is the gap between :

Accepted Answer

Primary and secondary case

Answer

Index and primary case

Answer

Introduction of infection and development of maximum infectivity

Answer

Transmission of infection from patient to another susceptible host

Question 10

In a village of 5,000 population, 50 persons suffered from cholera and 10 persons died. What will be the case fatality ratio?

Accepted Answer

20.0%

Answer

0.2%

Answer

5.0%

Answer

1.0%

Epidemiology — MCQs

Epidemiology — MCQs

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