UPSC-CMS 2025 - Community Medicine Practice Questions

Q: Many patients with unexplained rash and fever were reported from a village close to the Primary Health Centre (PHC). What is the first step in initiating the investigation of such an epidemic?

Confirm existence of epidemic. ***Confirm existence of epidemic*** - The initial and crucial step in any epidemiological investigation is to **verify if a true epidemic exists**, which involves comparing current disease incidence with expected levels. - This step helps to differentiate between a real outbreak and a normal fluctuation in disease occurrence or an artifact of increased reporting. *Defining the population at risk* - While important, identifying the **population at risk** comes after confirming an epidemic and is essential for calculating attack rates and understanding disease spread. - This step helps in understanding who might be exposed or susceptible, allowing for targeted interventions. *Rapid search for all cases* - A **rapid search for all cases** is a critical component of case finding once an epidemic has been confirmed and a case definition established. - This step helps in understanding the magnitude of the outbreak and identifying patterns of transmission. *Verification of diagnosis* - **Verification of diagnosis** is crucial for ensuring that reported cases meet the established case definition and to exclude other conditions. - This process helps to ensure the accuracy of data collected during the investigation and precedes further epidemiological analysis.

Q: John Snow's discovery that cholera is a waterborne disease was the outcome of which type of study?

Natural experiment. ***Natural experiment*** - John Snow's investigation of the 1854 cholera outbreak in London specifically involved observing the effects of **different water sources** on cholera rates among distinct populations. - This constituted a **natural experiment** because the exposure (water source) was not manipulated by the researcher but rather occurred naturally within the population. *Risk factor trial* - A risk factor trial would involve **deliberately exposing** or changing exposure to a risk factor in different groups to observe outcomes, which is unethical and was not done by Snow. - This type of study is usually **interventional** and aims to determine causality by actively managing variables. *Uncontrolled trial* - An uncontrolled trial typically involves an intervention but without a **comparison group**, making it difficult to attribute observed effects solely to the intervention. - Snow's study, conversely, involved comparing outcomes between groups (those using different water pumps). *Trial of aetiological agent* - A trial of an aetiological agent would involve **intentionally introducing** or removing the suspected disease-causing agent (e.g., cholera bacteria) to observe its effects. - John Snow did not perform such an interventional study; his work was observational, identifying associations in natural settings.

Q: A study was conducted to evaluate the diagnostic accuracy of ECG for detecting myocardial infarction. The results are shown in the 2x2 table below: Myocardial Infarction Present Absent Total ECG Positive 45 8,000 8,045 ECG Negative 5 32,000 32,005 Total 50 40,000 40,050 Consider the following statements: I. Sensitivity is 90%. II. Specificity is 80%. Which of the statements given above is/are correct?

Both I and II. **Both I and II** - **Sensitivity** = True Positives / (True Positives + False Negatives) = 45 / (45 + 5) = 45/50 = **0.90 or 90%** ✓ - **Specificity** = True Negatives / (True Negatives + False Positives) = 32,000 / (32,000 + 8,000) = 32,000/40,000 = **0.80 or 80%** ✓ - Both calculations are correct based on the 2×2 contingency table - **Sensitivity** measures the ability of the test to correctly identify those with disease (true positive rate) - **Specificity** measures the ability of the test to correctly identify those without disease (true negative rate) *I only* - Incorrect because Statement II (Specificity = 80%) is also correct, not just Statement I *II only* - Incorrect because Statement I (Sensitivity = 90%) is also correct, not just Statement II *Neither I nor II* - Incorrect because both statements are mathematically correct based on the given data

Q: Data obtained from hospital records is not a representative sample of the population. What are the reasons for this ? I. Mild cases and subclinical cases may be missed. II. Population served by a hospital usually cannot be defined. III. Cost of hospital care is not recorded. IV. Admission policy for cases can vary from hospital to hospital. Select the correct answer using the code given below :

I, II and IV. ***I, II and IV*** - Hospital records tend to miss **mild or subclinical cases** because these individuals may not seek hospital care, leading to an underrepresentation of the true disease prevalence. - The **population served by a hospital is often ill-defined**, making it difficult to generalize findings to a specific community or broader population. - **Admission policies vary between hospitals**, meaning the types of cases seen at one institution might differ significantly from another, affecting sample representativeness. *II and III only* - While the **population served by a hospital is often ill-defined** (II), the cost of hospital care not being recorded (III) does not directly make the sample unrepresentative of the population's health status or disease prevalence. - The lack of cost data primarily impacts financial analysis, not the epidemiologic representativeness of patient data. *II, III and IV* - The statement that the **population served by a hospital usually cannot be defined** (II) and that **admission policies vary** (IV) are valid reasons for non-representativeness. - However, the **cost of hospital care not being recorded** (III) is not a direct reason why hospital data would fail to represent disease patterns or demographics of the general population. *I and II only* - Missing **mild and subclinical cases** (I) and an **ill-defined target population** (II) are valid reasons for unrepresentative data. - However, this option omits the crucial point that **hospital admission policies vary** (IV), which significantly influences the types of cases included in hospital records and their generalizability.

Question 1

Many patients with unexplained rash and fever were reported from a village close to the Primary Health Centre (PHC). What is the first step in initiating the investigation of such an epidemic?

Accepted Answer

Confirm existence of epidemic

Answer

Defining the population at risk

Answer

Rapid search for all cases

Answer

Verification of diagnosis

Question 2

John Snow's discovery that cholera is a waterborne disease was the outcome of which type of study?

Accepted Answer

Natural experiment

Answer

Risk factor trial

Answer

Uncontrolled trial

Answer

Trial of aetiological agent

Question 3

A study was conducted to evaluate the diagnostic accuracy of ECG for detecting myocardial infarction. The results are shown in the 2x2 table below:

Myocardial Infarction
                    Present    Absent    Total
ECG Positive         45       8,000     8,045
ECG Negative          5      32,000    32,005
Total                50      40,000    40,050

Consider the following statements:
I. Sensitivity is 90%.
II. Specificity is 80%.

Which of the statements given above is/are correct?

Accepted Answer

Both I and II

Answer

Neither I nor II

Answer

II only

Answer

I only

Question 4

Data obtained from hospital records is not a representative sample of the population. What are the reasons for this ?
I. Mild cases and subclinical cases may be missed.
II. Population served by a hospital usually cannot be defined.
III. Cost of hospital care is not recorded.
IV. Admission policy for cases can vary from hospital to hospital.

Select the correct answer using the code given below :

Accepted Answer

I, II and IV

Answer

II and III only

Answer

II, III and IV

Answer

I and II only

UPSC-CMS 2025 — Community Medicine