Epidemiology Practice Questions

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: SARS infection case fatality rate of >50% is observed in patients of which age group?

> 65 years. ***> 65 years*** - Patients over 65 years old with **SARS** have been observed to have a **case fatality rate exceeding 50%**, indicating a significantly higher risk of severe outcomes and death in this age group. - This increased vulnerability is often attributed to **weakened immune responses** and higher prevalence of **comorbidities** in older adults. *< 20 yrs* - The case fatality rate for SARS in individuals under 20 years old is observed to be **very low**, typically less than 1%. - This age group generally experiences milder symptoms and has a **more robust immune response** compared to older populations. *20 - 40 years* - In the 20-40 year age group, the case fatality rate for SARS is typically **low to moderate**, generally ranging from 1-5%. - While they are at higher risk than younger individuals, their outcomes are significantly better than those in older age groups. *40 - 60 years* - Patients between 40 and 60 years old with SARS have a moderate case fatality rate, usually in the range of **6-15%**. - This age group shows an elevated risk compared to younger adults but does not reach the very high fatality rates seen in the elderly.

Q: During investigation of an epidemic, the area is declared free of epidemic when?

Twice the incubation period of the disease since occurrence of the last case. ***Twice the incubation period of the disease since occurrence of the last case*** - An epidemic is declared over when there have been no new cases for a period equal to **twice the maximum incubation period** of the disease. - This timeframe ensures that any individuals who might have been infected by the last known case would have developed symptoms (or completed their infectivity period) within this observation window. *Thrice the incubation period of the disease since occurrence of the last case* - This duration is **excessively long** and not the standard public health measure for declaring an epidemic free. - While it provides an even greater margin of safety, it is not the most **efficient or practical threshold** for public health interventions. *The longest incubation period for the disease* - Observing for only the **longest incubation period** is insufficient because a new case could still emerge at the very end of this period, potentially starting a new chain of transmission. - It does not account for the possibility of **secondary cases** occurring at the extreme end of the incubation period. *Incubation period for the disease plus two standard deviations* - This statistical measure is typically used to define the **range of normal variation** for biological data, not for epidemic declaration. - While it relates to the incubation period, it is **not the established public health standard** for determining the end of an epidemic.

Q: Which of the following statements about standardization is false?

Direct standardization is used when population is large. ***Direct standardization is used when population is large*** - This statement is **false**. Direct standardization is typically used when **age-specific rates for the study population are known** and stable, regardless of the overall population size. - Its purpose is to compare health events across populations while **adjusting for differences in age structure**, making it suitable even for smaller populations if the specific rates are reliable. *Most commonly used for age differences* - This statement is **true**. Standardization, particularly direct and indirect, is most frequently applied to control for **age differences** between populations when comparing health outcomes or rates. - While other factors like sex or socioeconomic status can be standardized, **age** is the most common and often the most critical confounding variable. *Age-specific rates are required in indirect standardization* - This statement is **true**. Indirect standardization relies on **age-specific rates from a standard population** to calculate expected numbers of events in the study population. - This method is particularly useful when the **age-specific rates for the study population are unknown** or unstable (e.g., due to small numbers), making data from a large, known standard population essential. *All are correct* - This statement is **false** because, as explained, the statement "Direct standardization is used when population is large" is incorrect. - This option would only be true if all other individual statements were accurate, which is not the case here.

Q: Why are standardized death rates used in health comparisons?

For valid comparison between populations with different demographic characteristics. ***For valid comparison between populations with different demographic characteristics*** - **Standardized death rates** adjust for differences in age structure between populations, allowing for a fairer and more accurate comparison of mortality burdens. - This adjustment is crucial because crude death rates can be misleading if one population is significantly older or younger than another, as age is a strong determinant of mortality. *Calculations are more accurate.* - While standardization improves the **validity of comparisons**, it does not inherently make the calculations themselves more "accurate" in a general sense; rather, it makes them more suitable for comparative purposes. - The accuracy of the underlying data (e.g., death registration, population counts) is a separate concern from the standardization process. *To avoid selection bias.* - **Selection bias** typically refers to issues in how individuals are chosen for a study or how data are collected, leading to an unrepresentative sample. - Standardized death rates address **confounding variables** (like age distribution) in population-level comparisons, rather than resolving individual-level selection bias. *None of the options.* - This option is incorrect because there is a valid reason among the choices provided for using standardized death rates. - The primary purpose of standardization is indeed to enable **valid comparisons** between populations with differing demographic profiles.

Q: In a class of 100 students, 40 are susceptible to chickenpox. If 28 students developed chickenpox within the next 2 weeks, what is the secondary attack rate (SAR) of chickenpox?

70%. **70% - Correct Answer** The **secondary attack rate (SAR)** measures the spread of disease among susceptible contacts after exposure to a primary case. It is calculated as: **SAR = (Number of new cases among susceptible contacts / Total number of susceptible contacts) × 100%** In this scenario: - New cases = 28 students - Susceptible contacts = 40 students - SAR = (28/40) × 100% = **70%** This is the correct application of the SAR formula, using only susceptible individuals as the denominator (not the total class of 100). *60% - Incorrect* - This would require 24 out of 40 susceptible students developing chickenpox (24/40 = 0.60) - Does not match the observed 28 cases *80% - Incorrect* - This would require 32 out of 40 susceptible students developing chickenpox (32/40 = 0.80) - Overestimates the number of cases compared to the observed 28 *90% - Incorrect* - This would require 36 out of 40 susceptible students developing chickenpox (36/40 = 0.90) - Significantly overestimates the attack rate and does not reflect the actual 28 cases observed

Q: Secondary attack rate of mumps?

75%. ***75%*** - The **secondary attack rate** for mumps is approximately **75%**, indicating its high transmissibility among susceptible household contacts. - This high rate underscores the importance of vaccination to prevent spread in close-contact settings. *85%* - While mumps is highly contagious, an 85% secondary attack rate is generally considered too high and not reflective of typical epidemiological data. - This percentage is more commonly associated with diseases like measles, which has an even higher transmissibility. *95%* - A 95% secondary attack rate is characteristic of highly contagious diseases like **measles**, which transmit very efficiently even in short, casual contacts. - Mumps, while highly infectious, does not typically reach this level of secondary attack rate. *< 50%* - A secondary attack rate of less than 50% would suggest lower transmissibility than what is observed for mumps. - Diseases with lower secondary attack rates are generally less prone to rapid outbreaks among close contacts.

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 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.

Question 1

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 2

SARS infection case fatality rate of >50% is observed in patients of which age group?

Accepted Answer

> 65 years

Answer

< 20 yrs

Answer

20 - 40 years

Answer

40 - 60 years

Question 3

Which of the following statements is true regarding the iceberg of disease?

Accepted Answer

The tip of the iceberg represents the clinical cases.

Answer

Screening is primarily done for the tip of the iceberg.

Answer

Hypertension is a classical example of the iceberg of disease.

Answer

The clinician is primarily concerned with the hidden portion of the iceberg.

Question 4

During investigation of an epidemic, the area is declared free of epidemic when?

Accepted Answer

Twice the incubation period of the disease since occurrence of the last case

Answer

Thrice the incubation period of the disease since occurrence of the last case

Answer

The longest incubation period for the disease

Answer

Incubation period for the disease plus two standard deviations

Question 5

Which of the following statements about standardization is false?

Accepted Answer

Direct standardization is used when population is large

Answer

Age specific rates are required in indirect standardization

Answer

All are correct

Answer

Most commonly used for age differences

Question 6

Why are standardized death rates used in health comparisons?

Accepted Answer

For valid comparison between populations with different demographic characteristics

Answer

Calculations are more accurate.

Answer

To avoid selection bias.

Answer

None of the options.

Question 7

In a class of 100 students, 40 are susceptible to chickenpox. If 28 students developed chickenpox within the next 2 weeks, what is the secondary attack rate (SAR) of chickenpox?

Accepted Answer

70%

Answer

60%

Answer

90%

Answer

80%

Question 8

Secondary attack rate of mumps?

Accepted Answer

75%

Answer

95%

Answer

< 50%

Answer

85%

Question 9

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 10

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

Epidemiology — MCQs

Epidemiology — MCQs

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