Investigation of an Epidemic — MCQs
Which of the following diseases requires airborne isolation with negative pressure rooms for the longest duration during active infection?
Under the original International Health Regulations, the internationally quarantinable diseases were -
An influenza pandemic is defined as:
Typhoid Mary is known in history to cause more than 1300 cases in her lifetime. This is an example of which of the following epidemic?
What is the secondary attack rate in a household with 9 susceptible individuals, where 1 individual becomes infected initially and 2 additional individuals become infected 2 days later?
The incubation period does not help in determining which of the following?
In the context of measles, which type of epidemic is characterized by all cases clustering within one incubation period?
Transition from increased prevalence of infectious and communicable diseases to man-made diseases is known as
What is the first step an epidemiologist takes in an epidemic investigation?
Which of the following is NOT a criterion for defining a polio epidemic?
Investigation of an Epidemic Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following diseases requires airborne isolation with negative pressure rooms for the longest duration during active infection?
- A. Cholera (severe cases)
- B. Measles (during outbreaks)
- C. Influenza
- D. Tuberculosis (Correct Answer)
Explanation: ***Tuberculosis*** - Requires **prolonged airborne isolation** in negative pressure rooms, often for **weeks to months** until the patient is no longer infectious (typically after 2-3 weeks of effective treatment and sputum conversion). - Patients with **active pulmonary TB** remain infectious for an extended period and require strict airborne precautions to prevent transmission through aerosol droplets. - TB isolation is among the most **rigorous and prolonged** compared to other infectious diseases due to its chronic nature and high transmissibility. *Cholera (severe cases)* - Requires **enteric/contact precautions** rather than airborne isolation. - Spreads through **fecal-oral route** via contaminated water and food. - Isolation duration is typically **shorter** (3-5 days) and focuses on sanitation and fluid management rather than airborne precautions. *Measles (during outbreaks)* - Does require **airborne isolation** due to high contagiousness via respiratory droplets. - However, isolation period is **much shorter** than TB—typically **4 days after rash onset** (or until immune recovery in immunocompromised). - Once the infectious period ends, isolation can be discontinued relatively quickly compared to TB. *Influenza* - Requires **droplet and contact precautions**, not strict airborne isolation for most strains. - Isolation period is **short** (typically **5-7 days** from symptom onset, or 24 hours after fever resolution with antivirals). - Standard surgical masks and droplet precautions are usually sufficient, unlike the N95 respirators and negative pressure rooms required for TB.
Question 2: Under the original International Health Regulations, the internationally quarantinable diseases were -
- A. Cholera
- B. All of the above (Correct Answer)
- C. Plague
- D. Yellow fever
Explanation: ***All of the above*** - **Cholera**, **plague**, and **yellow fever** were the three diseases designated as internationally quarantinable under the **original International Health Regulations (IHR)** before the 2005 revision. - These diseases were selected due to their potential for rapid international spread and serious public health impact, requiring coordinated global surveillance and response. - **Note:** The IHR (2005), which came into force in 2007, replaced this fixed list with a framework for assessing **Public Health Emergencies of International Concern (PHEIC)** using a decision algorithm. *Cholera* - **Cholera** is an acute diarrheal illness caused by *Vibrio cholerae* that can cause severe dehydration and death if untreated, with high potential for **epidemic spread**, particularly in areas with poor sanitation. - It was designated as quarantinable due to its rapid transmission via contaminated water and food. *Plague* - **Plague**, caused by the bacterium *Yersinia pestis*, has historically caused devastating pandemics and remains a concern due to its high fatality rate and potential for spread through **vector transmission** (fleas) or **person-to-person transmission via pneumonic plague**. - Its inclusion reflected its capacity to cause widespread morbidity and mortality. *Yellow fever* - **Yellow fever** is a viral hemorrhagic disease transmitted by *Aedes* mosquitoes, posing risk in tropical and subtropical regions of Africa and South America. - Its quarantinable status stemmed from its potential for rapid spread into non-endemic areas by infected travelers and the presence of **competent mosquito vectors globally**.
Question 3: An influenza pandemic is defined as:
- A. A worldwide epidemic of influenza caused by a new virus strain (Correct Answer)
- B. A localized outbreak of seasonal influenza
- C. An annual recurrence of influenza in winter months
- D. A gradual increase in influenza cases over several years
Explanation: ***A worldwide epidemic of influenza caused by a new virus strain*** - An influenza pandemic is defined as the **global spread of a novel influenza virus** to which the human population has **little or no immunity**. - According to WHO, a pandemic occurs when a new influenza virus emerges that is capable of **sustained human-to-human transmission** across **multiple countries and continents**. - The key defining features are: **worldwide geographic spread**, **novel virus strain**, and **lack of population immunity** leading to widespread illness. *A gradual increase in influenza cases over several years* - This is **incorrect** - pandemics can develop **rapidly**, not necessarily gradually over years. - Examples: the 2009 H1N1 pandemic spread globally within **weeks to months**, not years. - A gradual increase could describe endemic disease patterns, not the sudden emergence characteristic of pandemics. *A localized outbreak of seasonal influenza* - This describes a **local epidemic or outbreak**, not a pandemic. - The term "localized" is the opposite of pandemic, which requires **widespread geographic distribution**. - **Seasonal influenza** involves circulating strains with existing population immunity, unlike pandemic strains. *An annual recurrence of influenza in winter months* - This describes **seasonal/endemic influenza**, which occurs predictably with established viral strains. - Pandemics involve **novel strains** causing unexpected, widespread disease, not predictable annual patterns. - Seasonal flu is limited in severity due to existing immunity from prior exposure or vaccination.
Question 4: Typhoid Mary is known in history to cause more than 1300 cases in her lifetime. This is an example of which of the following epidemic?
- A. Propagated epidemic
- B. Common source continuous or repeated exposure epidemic (Correct Answer)
- C. Common source single exposure epidemic
- D. Long term or secular trend epidemic
Explanation: ***Common source continuous or repeated exposure epidemic*** - **Typhoid Mary** was a **chronic asymptomatic carrier** of *Salmonella Typhi*, meaning she continuously or repeatedly shed the bacteria. - As a cook, she **repeatedly exposed others to the pathogen** through contaminated food over many years, leading to numerous outbreaks. *Propagated epidemic* - A propagated epidemic occurs through **person-to-person transmission**, where the infection spreads sequentially over time, each infected person becoming a source for subsequent cases. - While Typhoid Mary eventually led to multiple cases, her primary role was as a continuous source rather than initiating a person-to-person chain where every new case infected another. *Common source single exposure epidemic* - This type of epidemic involves a **single, brief exposure** to the common source, such as a contaminated meal served once. - Typhoid Mary's numerous cases spanned years, indicating **multiple exposures** rather than a single event. *Long term or secular trend epidemic* - A **secular trend** refers to changes in disease frequency over **long periods**, often decades or centuries, reflecting gradual shifts in risk factors or environmental conditions. - Typhoid Mary's impact was a series of acute outbreaks over a shorter, defined period, not a gradual long-term trend.
Question 5: What is the secondary attack rate in a household with 9 susceptible individuals, where 1 individual becomes infected initially and 2 additional individuals become infected 2 days later?
- A. 50%
- B. 65%
- C. 25% (Correct Answer)
- D. 33%
Explanation: ***25%*** - The secondary attack rate is calculated as **(Number of secondary cases / Total number of susceptible contacts) * 100**. - In this scenario, there are 2 new cases among 8 susceptible contacts (initially 9 susceptible, minus the 1 primary case). So, (2 / 8) * 100 = **25%**. *33%* - This percentage would be relevant if there were 2 secondary cases out of 6 susceptible individuals, which is not the case here. - This calculation misrepresents the denominator by not correctly accounting for the initial prevalent case. *50%* - This would imply 2 secondary cases out of 4 susceptible individuals, which is not consistent with the given problem. - It would overestimate the secondary attack rate based on the provided numbers. *65%* - This percentage is significantly higher than what the given data suggests for the secondary attack rate. - It does not correspond to the calculation of 2 secondary cases among 8 susceptible individuals.
Question 6: The incubation period does not help in determining which of the following?
- A. Period of isolation
- B. Immunization (Correct Answer)
- C. Period of quarantine
- D. Identification of source of infection
Explanation: ***Immunization*** - The incubation period provides information about the disease progression from exposure to symptoms but does not directly guide the development or implementation of **immunization strategies**. - Immunization decisions are primarily based on the **disease's epidemiology**, severity, transmissibility, and vaccine efficacy, not the length of a single incubation period. *Period of isolation* - Knowing the incubation period helps determine how long an infected individual should be isolated to prevent transmission. - If the incubation period is short, isolation may be unnecessary, or if long, isolation may need to be prolonged until the infectious period is over. *Period of quarantine* - The incubation period is crucial for setting the duration of quarantine for exposed, but not yet symptomatic, individuals. - Quarantine typically lasts for the maximum incubation period to ensure that a person who develops the disease during this time is not able to transmit it to others. *Identification of source of infection* - By knowing the incubation period, epidemiologists can trace back the potential time of exposure, which is vital for identifying the **source of infection**. - This helps in targeted investigations to prevent further spread from the same source.
Question 7: In the context of measles, which type of epidemic is characterized by all cases clustering within one incubation period?
- A. Point source epidemic (Correct Answer)
- B. Continuous source epidemic
- C. Propagated epidemic
- D. Endemic
Explanation: ***Point source epidemic*** - This type of epidemic occurs when all cases are exposed to the same **common source** over a **brief period**, typically within one incubation period. - The rapid clustering of measles cases suggests a single exposure event to the virus, leading to simultaneous onset of symptoms. - The epidemic curve shows a sharp rise and fall within one incubation period. *Continuous source epidemic* - This involves ongoing exposure to the **common source** over an extended period, resulting in a prolonged epidemic curve with cases presenting over multiple incubation periods. - The epidemic curve shows a plateau pattern as exposure continues. *Propagated epidemic* - Also called **person-to-person epidemic**, this occurs when infection spreads through direct transmission from one person to another. - Cases appear over **several incubation periods** as the disease propagates through the population in successive generations. - The epidemic curve shows multiple peaks corresponding to successive waves of transmission. *Endemic* - An endemic disease is constantly present in a population at a **baseline level**, with a predictable number of cases over time, rather than a sudden clustering. - Measles, if endemic, would show a consistent pattern of cases, not a sudden outbreak over one incubation period.
Question 8: Transition from increased prevalence of infectious and communicable diseases to man-made diseases is known as
- A. Demographic transition
- B. Paradoxical transition
- C. Epidemiological transition (Correct Answer)
- D. Reversal of transition
Explanation: ***Epidemiological transition*** - This term describes the shift in **disease patterns** observed in many populations, moving from a predominance of **infectious and communicable diseases** to an increased prevalence of **chronic, non-communicable diseases** (often described as "man-made" due to their association with lifestyle and environmental factors). - This transition is typically linked to advancements in **public health**, sanitation, medicine, and changes in socioeconomic status. *Demographic transition* - This concept describes the historical shift from high **birth rates** and **death rates** to low birth rates and death rates as a country develops from a pre-industrial to an industrialized economic system. - While related to disease patterns through changes in population structure, it directly focuses on **population growth** and age distribution, not specific disease prevalence. *Paradoxical transition* - This is not a recognized or standard public health or demographic term for the described phenomenon. - The term "paradoxical" would imply a contradictory or unexpected outcome, which is not the primary descriptor for the shift in disease patterns. *Reversal of transition* - This term would imply a return to previous patterns, such as an increase in **infectious diseases** after a period of decline. - While possible in specific contexts (e.g., due to antibiotic resistance or weakened public health systems), it does not describe the initial shift from infectious to man-made diseases.
Question 9: What is the first step an epidemiologist takes in an epidemic investigation?
- A. Confirm the diagnosis (Correct Answer)
- B. Identify the prone people
- C. Identify the causative factors
- D. Identify the cases
Explanation: ***Confirm the diagnosis*** - The initial and most crucial step is to **confirm the diagnosis** of the disease in question to ensure that the reported cases are indeed suffering from the same condition. - This step helps to avoid misclassification and ensures the investigation focuses on a specific, confirmed health problem. *Identify the cases* - While essential, **identifying cases** usually follows initial diagnostic confirmation, as you need a clear case definition based on a confirmed diagnosis to correctly identify who is a case. - This involves defining who is considered a case based on symptoms, laboratory results, and epidemiological links. *Identify the prone people* - **Identifying prone people** refers to determining the population at risk, which is a subsequent step after understanding the confirmed disease and its initial pattern. - This step typically falls under characterizing the distribution of the disease (person, place, time) in the investigation. *Identify the causative factors* - **Identifying causative factors** is a later stage in the investigation, often involving analytical studies to test hypotheses, which can only occur effectively once the diagnosis is confirmed and cases are clearly defined and counted. - This step aims to understand *why* the epidemic is occurring, after establishing *what* is occurring.
Question 10: Which of the following is NOT a criterion for defining a polio epidemic?
- A. Caused by same virus type
- B. Cases should occur in same locality
- C. 2 or more cases
- D. Cases occurring during a 6 month period (Correct Answer)
Explanation: ***Correct: Cases occurring during a 6 month period*** - The definition of a polio epidemic primarily focuses on criteria like the number of cases, their geographical proximity, and the viral serotype causing the infection, not a specific duration of time over which cases occur. - While an outbreak naturally unfolds over a period, a fixed 6-month window is **not a formal defining criterion** for an epidemic, which typically emphasizes a sudden, significant increase above expected levels. *Incorrect: 2 or more cases* - An epidemic is generally defined by an **unusual increase in disease incidence**, and even two confirmed cases, especially in areas with low endemicity or where polio is eradicated, can signal an outbreak. - The presence of **two or more paralytic polio cases** within a specific area is often considered a critical threshold for declaring an epidemic, particularly for **wild poliovirus**. *Incorrect: Cases should occur in same locality* - For an epidemic to be declared, the cases must be **geographically linked** to indicate a common source or local transmission. - Cases spread across different, unconnected regions would suggest **sporadic occurrences** rather than a localized epidemic. *Incorrect: Caused by same virus type* - An epidemic implies a **common etiologic agent**, meaning the cases should be linked to the same serotype of **poliovirus** (e.g., wild poliovirus type 1). - If cases are caused by different serotypes, it indicates **multiple independent introductions** rather than a single epidemic outbreak.
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