Epidemiology Practice Questions

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.

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: 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: A housefly transmits any infectious agent by which of the following methods, most commonly?

Mechanical transmission. ***Mechanical transmission (Correct Answer)*** - Houseflies are **classic mechanical vectors** that transmit pathogens through physical transfer. - They pick up pathogens on their **legs, proboscis, or body hairs** from contaminated sources (feces, garbage) and physically transport them to food or other surfaces. - This method involves **no biological multiplication or development** of the pathogen within the fly. - Common diseases transmitted: **Typhoid, cholera, dysentery, diarrheal diseases, trachoma**. *Propagative transmission (Incorrect)* - This involves the **multiplication** of the pathogen within the vector, but no developmental changes. - Houseflies do **not** support pathogen multiplication in their bodies. - Example of this type: Mosquitoes transmitting **arboviruses** like dengue or Zika. *Cyclo-propagative transmission (Incorrect)* - The pathogen undergoes both **multiplication and developmental changes** within the vector. - Houseflies are **not biological vectors** and cannot support this process. - Classic example: **Malarial parasite** (Plasmodium) in Anopheles mosquitoes. *Cyclo-developmental transmission (Incorrect)* - The pathogen undergoes **developmental changes** within the vector but does not multiply. - Houseflies do **not** serve as intermediate hosts for pathogen development. - Example: **Filarial worms** in mosquitoes developing into infective larvae.

Q: Which of the following are criteria for cancer screening? I. Screening test should be sensitive and specific II. Screening test should be acceptable to the screened population III. The disease should be an uncommon one for screening to be effective IV. Disease should be recognisable at an early stage Select the correct answer using the code given below :

I, II and IV. ***I, II and IV*** - A successful **screening test** should be **sensitive** (correctly identify those with the disease) and **specific** (correctly identify those without the disease) to minimize false negatives and false positives. - For a screening program to be effective, the test must be **acceptable** to the target population to ensure high participation rates. The disease should also be **recognizable at an early stage** to allow for timely and effective intervention. *II, III and IV* - This option is partially correct as it includes acceptability and early recognition, but incorrectly states that the disease should be uncommon. In reality, screening is often more impactful for diseases with a higher prevalence. - The claim that the disease should be uncommon is incorrect; screening programs are often prioritized for relatively common diseases where early detection can significantly alter outcomes. *I, III and IV* - This option correctly identifies the need for a sensitive and specific test, and early disease recognition, but it incorrectly asserts that the disease should be an uncommon one. - Screening is generally most beneficial for diseases with a significant prevalence, allowing for a substantial impact on public health. *I, II and III* - This option accurately points to the necessity of a sensitive and specific test and its acceptability to the screened population, but it mistakenly suggests that the disease should be uncommon. - Effective screening targets diseases where early detection can lead to improved outcomes, which are often diseases with a notable burden in the population.

Q: A surgical department of a premier medical college conducted a study on rates of post-operative wound infection. The results of the study were negative for the proposed hypothesis. What should the department do with the results?

Report the negative results. **Report the negative results** - All research findings, whether positive or negative, contribute to the body of scientific knowledge and should be **ethically reported** to prevent publication bias. - Reporting negative results helps other researchers avoid duplicating efforts and can inform future study designs, potentially leading to a better understanding of the topic. *Label them as worthless* - Labeling negative results as "worthless" contradicts the principles of **scientific integrity** and promotes publication bias, where only positive findings are disseminated. - Even negative findings can provide crucial insights, indicating that a particular intervention or hypothesis is not supported, thus saving time and resources for future research. *Redo the study with a new hypothesis* - While forming new hypotheses may be necessary in some cases, redoing the study with a completely new hypothesis without reporting the initial negative results would be **unethical** and contribute to the problem of **publication bias**. - **New hypotheses** should ideally be formulated based on a comprehensive understanding of existing research, including negative findings. *Redesign the study and increase the sample size* - While redesigning the study and increasing sample size might be appropriate after the initial results have been reported and analyzed, the **immediate and ethical step** is to report the existing negative findings. - A larger sample size alone does not guarantee positive results; careful reevaluation of the methods and hypothesis is needed if the initial study was well-conducted.

Q: In which one of the following diseases are the source of infection and reservoir of infection the same ?

Hookworm infection. ***Hookworm infection*** - In hookworm infection, the **infected human host** is considered both the **source** and **reservoir** of infection in the epidemiological chain. - The adult worms live in the **human intestine** (reservoir), and humans excrete eggs in feces that contaminate soil, where larvae develop and subsequently infect other humans, perpetuating the cycle within the human population. - While larvae develop in soil, the **ultimate source and reservoir is the infected human**, as without human hosts, the transmission cycle cannot be maintained. *Tetanus* - The **reservoir** for tetanus is **soil and the gastrointestinal tract of animals**, where *Clostridium tetani* spores persist. - The **source of infection** is contaminated soil or rusty objects entering wounds. - Humans are **accidental hosts** (dead-end hosts) and do not serve as reservoirs, so source and reservoir are distinct (both environmental). *Cholera* - The **reservoir** for cholera is primarily **humans**, with *Vibrio cholerae* colonizing the intestinal tract. - The **source of infection** is typically **water or food contaminated with feces** from infected individuals. - While humans are the main reservoir, aquatic environments can serve as secondary environmental reservoirs, and the immediate source (contaminated water/food) is often considered distinct from the human reservoir in classical teaching. *Typhoid* - The **reservoir** for typhoid is exclusively **humans**, particularly chronic carriers who harbor *Salmonella typhi* in the gallbladder. - The **source of infection** is **food or water contaminated** by infected human carriers. - Although humans are the sole reservoir, the immediate source (contaminated food/water) is conventionally distinguished from the reservoir (the carrier), making them technically distinct in the transmission chain.

Q: Cross-over type of study designs are those in which each subject serves as his/her own control. In which of the following conditions is a cross-over study not suitable ?

If the drug of interest cures the disease. ***If the drug of interest cures the disease*** - A **crossover study** relies on subjects experiencing both treatment and control conditions, which is **not possible** if a drug cures the disease, as the initial treatment would eliminate the condition for the second phase. - The carryover effect of a cure would invalidate the comparison between the treatment and control periods, making subsequent observations on the same subject non-independent. *If the disease changes radically during the period of time required for the study* - **Radical changes in disease progression** would introduce significant **confounding variables**, making it difficult to attribute changes in outcome solely to the intervention. - The **baseline state** for the second treatment period would be vastly different from the first, violating the assumption of comparable conditions inherent in crossover designs. *None of the options* - This option is incorrect because there is a specific scenario among the choices where a crossover study is unsuitable, as detailed in the correct answer. *If the drug is effective during all stages of the disease* - A drug's effectiveness across all disease stages would actually **make a crossover study more suitable**, as the treatment effects could be consistently observed regardless of when the intervention is given. - This scenario would reduce the variability in response due to disease progression, allowing for a clearer comparison between treatment and control periods.

Q: Which one of the following is defined as "the average number of children a woman would have if she were to pass through her reproductive years, bearing children at the same rates as the women now in each age group" ?

Total Fertility Rate (TFR). **Total Fertility Rate (TFR)** - The **Total Fertility Rate (TFR)** is a measure of the average number of children a woman is expected to have over her lifetime, assuming current age-specific fertility rates. - It is a synthetic measure that reflects the reproductive patterns of a given population at a specific time. *Net Reproduction Rate (NRR)* - The **Net Reproduction Rate (NRR)** is similar to the Gross Reproduction Rate but also accounts for **mortality rates** among females before completing their reproductive years. - It measures the number of daughters a newborn girl can expect to have during her lifetime, considering current age-specific fertility and mortality rates. *General Fertility Rate (GFR)* - The **General Fertility Rate (GFR)** calculates the number of live births per 1,000 women of reproductive age (typically 15-49 years). - It is a broader measure than age-specific rates but does not project the total number of children a woman might have. *Age-Specific Fertility Rate (ASFR)* - An **Age-Specific Fertility Rate (ASFR)** measures the number of live births to women in a particular age group per 1,000 women in that same age group. - While it provides data for specific age cohorts, it does not combine these to give a lifetime average as described in the definition.

Q: Which of the following publications is/are brought out by the World Health Organization? 1. CD Alert 2. Morbidity and Mortality Weekly Report 3. Weekly Epidemiological Record Select the correct answer using the code given below.

3 only. ***3 only*** - The **Weekly Epidemiological Record (WER)** is the only publication in this list brought out by the **World Health Organization (WHO)**. - WER provides up-to-date information on **epidemiological events globally** and serves as an essential tool for **public health surveillance**. - **CD Alert** is published by the **National Centre for Disease Control (NCDC), India**, not WHO. - **Morbidity and Mortality Weekly Report (MMWR)** is published by the **U.S. Centers for Disease Control and Prevention (CDC)**, not WHO. *2 only* - The **MMWR** is a publication of the **CDC, USA**, not the WHO. - This option incorrectly attributes a CDC publication to WHO. *2 and 3* - While the **Weekly Epidemiological Record** is correctly a WHO publication, the **MMWR** is published by the **CDC, not WHO**. - This option is incorrect because it wrongly includes MMWR as a WHO publication. *1 and 2* - **CD Alert** is published by the **NCDC, India** (not WHO), and **MMWR** is published by the **CDC, USA** (not WHO). - This option is incorrect as neither publication is brought out by the WHO.

Question 1

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

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

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 4

A housefly transmits any infectious agent by which of the following methods, most commonly?

Accepted Answer

Mechanical transmission

Answer

Propagative transmission

Answer

Cyclo-propagative transmission

Answer

Cyclo-developmental transmission

Question 5

Which of the following are criteria for cancer screening?
I. Screening test should be sensitive and specific
II. Screening test should be acceptable to the screened population
III. The disease should be an uncommon one for screening to be effective
IV. Disease should be recognisable at an early stage
Select the correct answer using the code given below :

Accepted Answer

I, II and IV

Answer

II, III and IV

Answer

I, III and IV

Answer

I, II and III

Question 6

A surgical department of a premier medical college conducted a study on rates of post-operative wound infection. The results of the study were negative for the proposed hypothesis. What should the department do with the results?

Accepted Answer

Report the negative results

Answer

Label them as worthless

Answer

Redo the study with a new hypothesis

Answer

Redesign the study and increase the sample size

Question 7

In which one of the following diseases are the source of infection and reservoir of infection the same ?

Accepted Answer

Hookworm infection

Answer

Tetanus

Answer

Cholera

Answer

Typhoid

Question 8

Cross-over type of study designs are those in which each subject serves as his/her own control. In which of the following conditions is a cross-over study not suitable ?

Accepted Answer

If the drug of interest cures the disease

Answer

If the disease changes radically during the period of time required for the study

Answer

None of the options

Answer

If the drug is effective during all stages of the disease

Question 9

Which one of the following is defined as "the average number of children a woman would have if she were to pass through her reproductive years, bearing children at the same rates as the women now in each age group" ?

Accepted Answer

Total Fertility Rate (TFR)

Answer

Net Reproduction Rate (NRR)

Answer

General Fertility Rate (GFR)

Answer

Age-Specific Fertility Rate (ASFR)

Question 10

Which of the following publications is/are brought out by the World Health Organization?

1. CD Alert
2. Morbidity and Mortality Weekly Report
3. Weekly Epidemiological Record
Select the correct answer using the code given below.

Accepted Answer

3 only

Answer

2 only

Answer

2 and 3

Answer

1 and 2

Epidemiology — MCQs

Epidemiology — MCQs

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