Epidemiology Practice Questions

Q: Best indicator for spread of TB in a community?

Annual infection rate. ***Annual infection rate*** - The **Annual Infection Rate (ARI)** is the gold standard indicator for measuring TB spread in a community - It measures the rate at which new TB infections occur in a tuberculin-negative population over one year - ARI directly reflects **recent transmission** and the force of infection in the community - WHO and Park's Textbook recommend ARI as the best epidemiological indicator for TB transmission - Calculated through tuberculin surveys showing conversion from negative to positive - An ARI of 1% indicates 1% of uninfected individuals become infected per year *Incidence of new cases* - Incidence measures new **disease cases** (active TB), not new infections - Only 5-10% of TB infections progress to active disease, often after years of latency - Incidence is affected by case detection rates, diagnostic capacity, and healthcare access - It underestimates actual transmission occurring in the community *Prevalence of infection* - **Prevalence** indicates total existing cases (both old and new) at a point in time - Influenced by both new infections and duration of infection/disease - Does not specifically measure the rate of ongoing transmission *Case rate* - **Case rate** refers to the number of active disease cases per population - Similar to prevalence, it doesn't isolate new transmission events - Less sensitive for detecting changes in transmission dynamics

Q: Strength of association of outcome and risk factor is measured by?

Relative risk. ***Relative risk*** - **Relative risk (RR)** directly measures the **strength of association** between exposure to a risk factor and the development of an outcome. - It is calculated as the ratio of the **incidence rate** in the exposed group to the incidence rate in the unexposed group. *Attributable risk* - **Attributable risk (AR)** measures the **absolute difference** in outcome rates between exposed and unexposed groups, indicating the extra cases due to exposure. - It quantifies the **public health impact** or burden of disease that can be attributed to the exposure, rather than the strength of association. *Population attributable risk* - **Population attributable risk (PAR)** estimates the proportion of disease incidence in the **total population** that is attributable to an exposure. - It considers both the **strength of the association** and the **prevalence of the exposure** in the population, making it more about public health impact than individual strength of association. *None of the options* - This option is incorrect because **relative risk** is a fundamental epidemiological measure for determining the strength of association.

Q: What is the definition of an endemic disease?

Disease occurring regularly in expected frequency. ***Disease occurring regularly in expected frequency*** - An **endemic disease** is consistently present in a population within a given geographic area at an **expected frequency**. - This implies that the disease is **always circulating** and has a baseline level of incidence. *Disease occurring in excess of expected frequency* - This definition describes an **epidemic**, where the disease occurrence is significantly higher than what is normally expected for that population. - While an endemic disease can become an epidemic, the core definition of endemic does not include an excess frequency. *Disease affecting a large population* - Affecting a large population is not the defining characteristic of an endemic disease; rather, it refers to the **scale** or **reach** of a disease. - A disease can affect a large population without being endemic, such as a widespread pandemic that is not regularly present in every affected region. *Disease occurring irregularly* - Irregular occurrence describes a more **sporadic** pattern of disease, where cases appear inconsistently and without a predictable frequency. - An **endemic disease** is characterized by its regular and predictable presence, even if the number of cases fluctuates within expected limits.

Q: Which of the following statements is not true regarding the International Classification of Diseases?

It was devised by UNICEF. ***It was devised by UNICEF*** **(CORRECT - This statement is FALSE)** - The **International Classification of Diseases (ICD)** was developed and maintained by the **World Health Organization (WHO)**, not UNICEF. - **UNICEF** focuses on children's welfare and health, while **WHO** is the primary international health agency responsible for global health standards. - Since the question asks for the statement that is **NOT TRUE**, this is the correct answer. *It is revised once in 10 years* **(Incorrect - This statement is TRUE)** - The **ICD** is indeed typically revised approximately every **10 years** to incorporate new medical knowledge, diseases, and public health needs. - This regular revision cycle ensures the classification remains relevant and up-to-date with medical advancements and epidemiological trends. *It is accepted for National and International use* **(Incorrect - This statement is TRUE)** - The **ICD** is widely accepted and used globally by countries for **mortality and morbidity statistics**, health management, and reimbursement systems. - Its standardization allows for consistent **data collection** and comparison of health information across different regions and countries. *The 10th revision consists of 22 major chapters* **(Incorrect - This statement is TRUE)** - **ICD-10** (the 10th revision) is structured into **22 chapters**, each covering a specific category of diseases and health problems. - These chapters organize diagnoses logically, facilitating **data coding** and analysis in healthcare.

Q: What is the expected effect on incidence [I] and prevalence [P] when an effective treatment for a disease is introduced in a community?

P will decrease & I will remain the same. ***P will decrease & I will remain the same*** - An effective treatment reduces the **duration of disease** by curing existing cases faster, which directly decreases **prevalence** (P = Incidence × Duration) - **Incidence** measures the rate of *new cases* occurring, which is unaffected by treatment of existing cases, so **incidence remains unchanged** - This is the fundamental epidemiological principle for treatment interventions *No change in P & I* - Incorrect because effective treatment shortens disease duration, which must reduce the number of existing cases at any given time - **Prevalence** will definitely decrease when cases recover faster *Both P & I will decrease* - While treatment correctly decreases **prevalence** by shortening disease duration, it does not prevent *new infections* from occurring - **Incidence** (new case rate) remains unchanged unless there's a preventive intervention like vaccination or behavioral change *P will decrease & I will increase* - Correctly identifies that **prevalence** decreases with effective treatment - However, there's no mechanism by which treatment would increase **incidence** of new cases - Treatment affects existing patients, not the rate of new infections

Q: Which measure is considered crucial for formulating a National Health Policy?

Proportion of cases linked to exposure (Attributable risk). ***Proportion of cases linked to exposure (Attributable risk)*** - **Attributable risk** quantifies the proportion of disease cases in a population that can be attributed to specific **exposures**. - This measure is crucial for health policy as it helps prioritize interventions by identifying diseases and their causative factors that, if eliminated, would lead to the largest reduction in disease burden. *Measure of association between exposure and outcome (Relative risk)* - **Relative risk** indicates the strength of the association between an exposure and an outcome, comparing the risk of disease in exposed versus unexposed groups. - While important for understanding etiology, it doesn't directly quantify the **health burden** in the population that could be prevented by removing the exposure. *Frequency of new disease cases (Incidence rate)* - **Incidence rate** measures the rate at which new cases of a disease occur in a population over a specified period. - While it provides insight into disease spread, it doesn't directly identify how much of that spread is **preventable** by addressing specific risk factors for policy formulation. *Estimate of exposure-outcome odds (Odds ratio)* - The **odds ratio** is an estimate of the likelihood of an outcome occurring given exposure, usually in case-control studies. - Similar to relative risk, it indicates the **strength of association** but doesn't directly translate into the preventable disease burden at a population level.

Q: Major reservoir of KFD?

Squirrels. ***Squirrels*** - **Squirrels** are considered a major reservoir for the Kyasanur Forest Disease (KFD) virus because they can carry the virus without showing severe symptoms themselves, allowing for viral persistence in nature. - The virus can be transmitted from infected squirrels to ticks, which then can spread the infection to other animals or humans. *Human* - Humans are considered **incidental hosts** for KFD, meaning they can become infected but do not typically play a significant role in maintaining the virus in nature. - While humans can experience severe disease, they do not serve as a reservoir for further transmission to other vectors or hosts. *Cattle* - **Cattle** are not typically considered a reservoir for the Kyasanur Forest Disease virus. - They can be exposed to KFD but are not known to sustain the viral cycle or transmit it effectively to ticks or other animals. *Monkey* - While KFD is often associated with **monkey deaths** (especially black-faced langurs and bonnet macaques), these animals are considered **amplifying hosts** rather than primary reservoirs. - Monkeys experience severe disease and high mortality, making them good indicators of viral activity but not long-term carriers for sustained transmission.

Q: A screening test has sensitivity of 90% and specificity of 99%. The prevalence of disease under investigation is 5 per 1000 population. What is the PPV of the given screening test?

33. ***33*** * **Positive Predictive Value (PPV)** = \[Sensitivity \times Prevalence] / \[(Sensitivity \times Prevalence) + (1 – Specificity) \times (1 – Prevalence)] * Here, 0.9 x 0.005 / \[(0.9 x 0.005) + (1-0.99) x (1-0.005)] = 0.0045 / \[0.0045 + (0.01 x 0.995)] = 0.0045 / \[0.0045 + 0.00995] = 0.0045 / 0.01445 ≈ 0.3114 or 31.14%. Converting to a percentage closest to the answer choices, it would be 33%. *10* * This value would be obtained if there was an error in calculating either the **prevalence** of the disease or the contribution of false positives to the total positive tests. * Inaccuracies in the formula or arithmetic would lead to results far from the correct PPV. *70* * This value suggests a much higher **prevalence** or a significantly lower number of **false positives** than indicated by the given sensitivity, specificity, and prevalence. * Such a high PPV is inconsistent with a low disease prevalence (0.5%) and a relatively high false positive rate (1-specificity = 1%). *99* * This value is close to the given **specificity**, which is the probability of a true negative test among individuals without the disease, not the PPV. * A PPV of 99% would be extremely high for a disease with a prevalence of 0.5% and would typically require a much higher specificity and/or sensitivity.

Q: What is the significance of the 1st of July in demographic studies?

1st July. ***1st July*** - The **1st of July** is often considered the **mid-year population estimate** in demographic studies. - This date is crucial for calculating rates (e.g., birth rates, death rates) and making projections, as it provides a standardized reference point that balances out seasonal population fluctuations. *1st January* - While a significant date for many annual administrative purposes, the **1st of January** represents the beginning of the year, not the mid-point. - Using this date for population counts can sometimes overemphasize the population at the start of a new calendar cycle, potentially skewing annual rate calculations. *1st September* - The **1st of September** falls in the third quarter of the year and does not represent a standard mid-year point for demographic estimations. - This date has no widely recognized statistical significance for population estimation in demographic contexts. *15th June* - The **15th of June** is close to the middle of the year but is not the conventionally adopted date for mid-year population estimates. - Demographers prefer standard, easily replicable dates for consistency across regions and studies.

Question 1

Best indicator for spread of TB in a community?

Accepted Answer

Annual infection rate

Answer

Prevalence of infection

Answer

Incidence of new cases

Answer

Case rate

Question 2

Strength of association of outcome and risk factor is measured by?

Accepted Answer

Relative risk

Answer

Attributable risk

Answer

Population attributable risk

Answer

None of the options

Question 3

What does the secondary attack rate measure?

Accepted Answer

The proportion of susceptible people who become infected after exposure to a primary case

Answer

The ability of a disease to spread from one person to another

Answer

The ability of a disease to cause death

Answer

The rate at which a disease progresses in severity

Question 4

What is the definition of an endemic disease?

Accepted Answer

Disease occurring regularly in expected frequency

Answer

Disease affecting a large population

Answer

Disease occurring in excess of expected frequency

Answer

Disease occurring irregularly

Question 5

Which of the following statements is not true regarding the International Classification of Diseases?

Accepted Answer

It was devised by UNICEF

Answer

It is revised once in 10 years

Answer

It is accepted for National and International use

Answer

The 10th revision consists of 22 major chapters

Question 6

What is the expected effect on incidence [I] and prevalence [P] when an effective treatment for a disease is introduced in a community?

Accepted Answer

P will decrease & I will remain the same

Answer

No change in P & I

Answer

Both P & I will decrease

Answer

P will decrease & I will increase

Question 7

Which measure is considered crucial for formulating a National Health Policy?

Accepted Answer

Proportion of cases linked to exposure (Attributable risk)

Answer

Measure of association between exposure and outcome (Relative risk)

Answer

Frequency of new disease cases (Incidence rate)

Answer

Estimate of exposure-outcome odds (Odds ratio)

Question 8

Major reservoir of KFD?

Accepted Answer

Squirrels

Answer

Human

Answer

Cattle

Answer

Monkey

Question 9

A screening test has sensitivity of 90% and specificity of 99%. The prevalence of disease under investigation is 5 per 1000 population. What is the PPV of the given screening test?

Accepted Answer

33

Answer

10

Answer

70

Answer

99

Question 10

What is the significance of the 1st of July in demographic studies?

Accepted Answer

1st July

Answer

1st January

Answer

1st September

Answer

15th June

Epidemiology — MCQs

Epidemiology — MCQs

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