Epidemiology Practice Questions

Q: After attending a birthday party in a hostel around 50 students reported having loose stools, fever and a few reported vomiting. This outbreak can be identified as what type of outbreak ?

Common point source only. ***Common point source only*** - This outbreak shows all characteristics of a **common point source (point source) outbreak** where multiple individuals were exposed to the same contaminated source at a **single time and place** (the birthday party). - The symptoms (loose stools, fever, vomiting) all represent **clinical manifestations of food poisoning**, not evidence of secondary transmission. - Common point source outbreaks typically show a **sharp rise in cases followed by a rapid decline**, with all cases occurring within **one incubation period** of the exposure. - This is the classic pattern seen in **foodborne outbreaks** at events like parties, weddings, or gatherings. *Both propagated and common point source* - There is **no evidence of person-to-person transmission** or secondary cases in this scenario. - Vomiting is simply a **symptom of the foodborne illness**, not an indicator of propagated spread. - A mixed outbreak would require evidence of **successive waves of cases** beyond the initial exposure, which is not described here. *Common source continuous* - Continuous common source outbreaks occur when exposure to the contaminated source is **prolonged or intermittent** over time, creating a plateau in the epidemic curve. - This scenario describes a **single event** (birthday party) with acute exposure, not ongoing contamination. - Examples of continuous source outbreaks include contaminated water supplies or ongoing food contamination at a restaurant. *Propagated only* - Propagated outbreaks are characterized by **person-to-person transmission** leading to successive waves of cases over **multiple incubation periods**. - This scenario has a clear **point source exposure** (birthday party) as the initiating event, not person-to-person spread. - Examples of propagated outbreaks include measles, chickenpox, or other communicable diseases spreading through a population.

Q: In a town with one lakh population (1,00,000) there are a total of 2500 live births in a year. There were 75 total deaths of children before the age of one month, total 200 deaths before the age of one year, and a total 300 deaths before the age of three years. Which of the following statements regarding Infant Mortality Rate (IMR) of the town for the given year are correct? 1. The denominator is 1,00,000 2. The IMR of the town is higher than the current national average of IMR for India 3. The numerator is the number of children dying before the age of one month 4. The IMR of the town is 80 per 1000 live births

2 and 4 only. **IMR Formula:** Infant Mortality Rate = (Number of deaths under 1 year of age / Total live births in the same year) × 1000 **Analysis of each statement:** **Statement 1:** "The denominator is 1,00,000" - **INCORRECT** - The denominator for IMR is the **total number of live births (2,500)**, not the total population (1,00,000) - Population is not used in IMR calculation **Statement 2:** "The IMR of the town is higher than the current national average of IMR for India" - **CORRECT** - Calculated IMR = (200 deaths / 2,500 live births) × 1000 = **80 per 1000 live births** - India's current national IMR ≈ 27-28 per 1000 live births (as of 2020-2022 data) - 80 is significantly higher than the national average **Statement 3:** "The numerator is the number of children dying before the age of one month" - **INCORRECT** - The numerator for IMR is **deaths before the age of one year (200)**, not before one month - Deaths before one month (75) constitute the numerator for **Neonatal Mortality Rate**, not IMR **Statement 4:** "The IMR of the town is 80 per 1000 live births" - **CORRECT** - Calculation: (200 / 2,500) × 1000 = 80 per 1000 live births - This is the accurate IMR for the town ***Correct Answer: 2 and 4 only*** - Both statements 2 and 4 are correct as shown above - Statements 1 and 3 contain fundamental errors about the IMR formula components

Q: Which one of the following is a famous large prospective study that helped establish risk factors for coronary heart disease ?

Framingham study. ***Framingham study*** - The **Framingham Heart Study** is a landmark **long-term prospective cohort study** that began in 1948 in Framingham, Massachusetts, to identify common factors or characteristics that contribute to **cardiovascular disease (CVD)**. - This study has been instrumental in identifying major **CVD risk factors** such as high blood pressure, high cholesterol, smoking, obesity, diabetes, and physical inactivity. *Pittsburgh study* - While Pittsburgh is a hub for medical research, there isn't a single "Pittsburgh study" that holds the same widespread recognition for establishing **cardiovascular risk factors** as the Framingham study. - Various studies from Pittsburgh institutions might contribute to cardiovascular research, but none are as globally recognized for this specific contribution. *Adelaide study* - The "Adelaide study" generally refers to research conducted in Adelaide, Australia, which has produced various medical findings. - However, it is not known as a prominent, large-scale prospective study specifically designed to establish widespread **coronary heart disease risk factors** in the same league as the Framingham Heart Study. *Birmingham study* - Many medical studies are conducted in Birmingham (both in the UK and USA), but there isn't one definitive "Birmingham study" with the historical significance and impact on identifying **coronary heart disease risk factors** that the Framingham study has. - Research from Birmingham typically contributes to various medical fields, but not specifically as the primary source for these fundamental risk factor discoveries.

Q: Which one of the following best explains the relationship among Prevalence (P), Incidence (I) and Duration (D) of a disease given the assumption that the population is stable ?

P = I x D. **Fundamental Epidemiological Relationship:** In a stable population with endemic disease, the relationship between prevalence, incidence, and duration is expressed as: **Prevalence = Incidence × Average Duration (P = I × D)** ***P = I × D*** - This is the **correct formula** that describes the relationship under conditions of a **stable population** and **endemic disease**. - Prevalence is directly proportional to both the incidence rate and the average duration of the disease. - This formula reflects that the number of existing cases (prevalence) equals the rate at which new cases occur (incidence) multiplied by how long people have the disease (duration). - Example: If incidence = 10 cases/1000/year and average duration = 5 years, then prevalence = 50 cases/1000. *I = P × D* - This formula incorrectly suggests that incidence increases with both prevalence and duration. - This would mean that longer disease duration causes higher incidence, which is illogical. - Correctly rearranged, this would be I = P/D (incidence equals prevalence divided by duration). *D = P × I* - This formula incorrectly states that duration is the product of prevalence and incidence. - This would mean higher incidence causes longer duration, which is epidemiologically incorrect. - Correctly rearranged, this would be D = P/I (duration equals prevalence divided by incidence). *I = P + D* - This formula implies a simple additive relationship, which is **epidemiologically invalid**. - Prevalence, incidence, and duration are related **multiplicatively**, not additively, in a steady state. - This equation has no basis in epidemiological theory.

Q: In which one of the following study designs, the unit of study involves populations rather than individuals ?

Ecological studies. ***Correct: Ecological studies*** - **Ecological studies** analyze health-related data at a population level, such as countries or communities, rather than individual patients. - They are used to observe correlations between exposure and outcome among different groups or over time. - The unit of analysis is the **population or group**, not individuals. *Incorrect: Cross-sectional studies* - **Cross-sectional studies** examine individuals at a single point in time to determine the prevalence of a disease or exposure. - While they can describe populations, the unit of observation and analysis remains the **individual**. *Incorrect: Cohort studies* - **Cohort studies** follow groups of individuals (cohorts) over time to investigate the incidence of an outcome and its association with specific exposures. - The primary unit of study is the **individual**, who is tracked for disease development. *Incorrect: Case-control studies* - **Case-control studies** compare individuals with a disease (cases) to individuals without the disease (controls) to identify past exposures. - This design focuses on **individual-level data** to determine risk factors.

Q: Sullivan’s index is an indicator of:

Disability. ***Disability*** - Sullivan's index, also known as **disability-free life expectancy**, is a measure that combines **mortality** and **morbidity** data to estimate the expected years an individual will live without disability. - It's a key indicator of the average number of years a person can expect to live in a **healthy or non-disabled state.** *Morbidity* - While related to morbidity, Sullivan's index specifically measures the **absence of disability**, rather than just the presence of disease or illness. - **Morbidity** refers to the state of being diseased or unhealthy, without necessarily quantifying the impact on daily function. *Mortality* - **Mortality** refers to the death rate or the number of deaths in a population. Sullivan's index uses mortality data in its calculation but is not solely an indicator of mortality. - It combines mortality with information on disability to provide a more nuanced picture of **population health.** *Health care delivery* - **Health care delivery** refers to the organization and provision of medical services. Sullivan's index measures health outcomes and does not directly indicate the quality or efficiency of healthcare delivery systems. - While improved healthcare can influence disability-free life expectancy, the index itself is a **health status measure**, not a healthcare system measure.

Q: ‘Spot map’ in epidemiological studies refer to variation in the distribution of a disease at:

Local level. ***Local level*** - A **spot map** is an epidemiological tool used to visualize the geographical distribution of disease cases within a **small, defined area**, such as a neighborhood or a single city. - It helps in identifying **clusters or hot-spots** of disease occurrence, which can be crucial for locating potential sources of infection or environmental hazards. *International level* - While disease distribution can be mapped internationally, a "spot map" specifically refers to a **finer-grain analysis** at a much smaller geographical scale, not across multiple countries. - Maps at the international level are often used for **global burden of disease** studies or pandemic tracking, which require broader summaries rather than individual case plotting. *Rural – urban level* - Mapping at the rural-urban level indicates differences between these two broad categories, but a spot map provides even more specific detail within those areas. - It shows the precise location of cases, allowing for insights into localized environmental or social factors, rather than just a general rural vs. urban comparison. *National level* - National-level mapping provides an overview of disease prevalence or incidence across an entire country, which is a much larger scale than a spot map. - A spot map is designed to highlight **precise locations** of cases within a more contained geographical area, making it less suitable for broad national-level trends.

Q: Severity of a disease is measured by:

Case fatality rate. ***Case fatality rate*** - The **case fatality rate (CFR)** directly measures the **severity** of a disease by indicating the proportion of individuals diagnosed with a disease who ultimately die from it. - A higher CFR implies a more lethal or severe disease. *Incidence rate* - The **incidence rate** measures the **frequency of new cases** of a disease in a population over a specified period. - It reflects how quickly a disease is spreading, not its severity. *Attributable risk* - **Attributable risk (AR)** quantifies the proportion of disease incidence in an exposed group that can be attributed to the exposure. - It measures the **public health impact** of an exposure, not the inherent severity of the disease itself. *Relative risk* - **Relative risk (RR)** compares the probability of an event (e.g., disease development) in an **exposed group** to the probability of the event in an **unexposed group**. - It indicates the **strength of association** between an exposure and a disease, not the severity of the disease in affected individuals.

Q: An outbreak of Viral Hepatitis was reported from a town between June and August of a particular year. 60% of cases occurred in July. Exposure of the community to infection is from:

A single source for a short period. ***A single source for a short period*** - This describes a **point source outbreak**, the classic pattern seen in this scenario - **60% of cases in July** indicates exposure occurred over a **brief period** (likely days to weeks before July) - The 3-month span (June-August) represents the **distribution of cases around the incubation period** of viral hepatitis (typically 2-6 weeks for Hepatitis A) - Common examples: **contaminated water supply**, food at a community gathering, or other single exposure event - This is the **textbook presentation** of a point source epidemic with a characteristic sharp peak *Multiple sources for a short period* - This would produce **multiple peaks** or an irregular epidemic curve, not a single peak in July - Multiple sources would not create the concentrated 60% clustering observed - The pattern described is too uniform for multiple independent sources *A common single source for prolonged periods* - This describes a **continuous common source outbreak** with an extended epidemic curve - Cases would be **distributed more evenly** across June-August without a sharp peak - Example: ongoing contamination of a water supply over months - The 60% concentration in July rules out this pattern *Multiple sources over prolonged periods* - This would result in **endemic disease** or a very flat, prolonged epidemic curve - No sharp peak would be observed - The temporal clustering contradicts this pattern

Q: Due to which of the following does seasonal trend of a disease occur? 1. Vector variation 2. Environmental factors 3. Change in herd immunity Select the correct answer using the code given below:

1, 2 and 3. ***1, 2 and 3*** - **Vector variation** (e.g., mosquito populations increasing during warmer months) is a critical factor causing seasonal patterns in vector-borne diseases like malaria, dengue, and Japanese encephalitis. - **Environmental factors** such as temperature, humidity, and rainfall directly affect pathogen survival, vector breeding, transmission efficiency, and host susceptibility, leading to characteristic seasonal patterns (e.g., respiratory infections in winter, diarrheal diseases in summer). - **Changes in herd immunity** can contribute to temporal disease patterns, though this factor more commonly drives long-term cyclical patterns (multi-year cycles) rather than short-term seasonal variations. The accumulation of susceptible individuals (through births) and waning immunity can influence disease occurrence patterns over time. *2 and 3 only* - This option incorrectly excludes **vector variation**, which is a primary determinant of seasonality for many infectious diseases, particularly arthropod-borne infections. - Vector activity shows marked seasonal fluctuations that directly correlate with disease incidence. *1 and 3 only* - This option incorrectly excludes **environmental factors**, which are fundamental drivers of seasonal disease patterns. - Temperature, humidity, precipitation, and other climatic variables directly influence pathogen viability, vector ecology, and human behavioral patterns that affect disease transmission. *1 only* - This option is too restrictive, considering only **vector variation** while neglecting the significant contributions of **environmental factors** and **temporal changes in population immunity** to disease occurrence patterns. - Seasonal trends result from complex interactions among multiple factors.

Question 1

After attending a birthday party in a hostel around 50 students reported having loose stools, fever and a few reported vomiting. This outbreak can be identified as what type of outbreak ?

Accepted Answer

Common point source only

Answer

Common source continuous

Answer

Propagated only

Answer

Both propagated and common point source

Question 2

In a town with one lakh population (1,00,000) there are a total of 2500 live births in a year. There were 75 total deaths of children before the age of one month, total 200 deaths before the age of one year, and a total 300 deaths before the age of three years. Which of the following statements regarding Infant Mortality Rate (IMR) of the town for the given year are correct?

1. The denominator is 1,00,000
2. The IMR of the town is higher than the current national average of IMR for India
3. The numerator is the number of children dying before the age of one month
4. The IMR of the town is 80 per 1000 live births

Accepted Answer

2 and 4 only

Answer

1, 2 and 4

Answer

1 and 3 only

Answer

2 only

Question 3

Which one of the following is a famous large prospective study that helped establish risk factors for coronary heart disease ?

Accepted Answer

Framingham study

Answer

Pittsburgh study

Answer

Adelaide study

Answer

Birmingham study

Question 4

Which one of the following best explains the relationship among Prevalence (P), Incidence (I) and Duration (D) of a disease given the assumption that the population is stable ?

Accepted Answer

P = I x D

Answer

I = P x D

Answer

D = P x I

Answer

I = P + D

Question 5

In which one of the following study designs, the unit of study involves populations rather than individuals ?

Accepted Answer

Ecological studies

Answer

Cross-sectional studies

Answer

Cohort studies

Answer

Case-control studies

Question 6

Sullivan’s index is an indicator of:

Accepted Answer

Disability

Answer

Morbidity

Answer

Mortality

Answer

Health care delivery

Question 7

‘Spot map’ in epidemiological studies refer to variation in the distribution of a disease at:

Accepted Answer

Local level

Answer

International level

Answer

Rural – urban level

Answer

National level

Question 8

Severity of a disease is measured by:

Accepted Answer

Case fatality rate

Answer

Incidence rate

Answer

Attributable risk

Answer

Relative risk

Question 9

An outbreak of Viral Hepatitis was reported from a town between June and August of a particular year. 60% of cases occurred in July. Exposure of the community to infection is from:

Accepted Answer

A single source for a short period

Answer

Multiple sources over prolonged periods

Answer

Multiple sources for a short period

Answer

A common single source for prolonged periods

Question 10

Due to which of the following does seasonal trend of a disease occur?

1. Vector variation
2. Environmental factors
3. Change in herd immunity

Select the correct answer using the code given below:

Accepted Answer

1, 2 and 3

Answer

2 and 3 only

Answer

1 and 3 only

Answer

1 only

Epidemiology — MCQs

Epidemiology — MCQs

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