Epidemiology Practice Questions

Q: Incubation period of Salmonella typhi -

3-21 days. ***3-21 days*** - The typical incubation period for **Salmonella Typhi**, the bacterium causing typhoid fever, ranges from **3 to 21 days**. - This period allows the bacteria to multiply in the host before symptoms such as fever, headache, and malaise begin to appear. *2-5 days* - This incubation period is generally too short for **typhoid fever**, which typically has a longer course due to the pathogen's systemic spread. - Shorter incubation periods are more characteristic of other forms of **salmonellosis**, such as gastroenteritis. *14-25 days* - While overlap exists, a consistent range of **14 to 25 days** tends to skew towards the longer end of the typical incubation period, potentially missing earlier presentations. - The **3-21 day range** is more commonly cited in medical literature as the average window. *0-60 days* - An incubation period of **0-60 days** is excessively broad and lacks clinical precision for **typhoid fever**. - While rare cases might fall outside the typical range, this option includes an implausible immediate onset (0 days) and an overly protracted maximum duration.

Q: Disease elimination is helped by-

Herd immunity. ***Herd immunity*** - **Herd immunity** occurs when a large percentage of a population becomes immune to an infectious disease, providing indirect protection to those who are not immune. This significantly reduces the transmission chain and can stop the spread of a disease, aiding in its elimination. - When the proportion of immune individuals reaches a certain threshold, the **reproductive number (R0)** of the pathogen drops below 1, meaning each infected person transmits the disease to fewer than one other person on average, leading to a decline and eventual elimination of the disease. - **Examples:** Smallpox elimination was achieved through vaccination creating herd immunity; polio elimination efforts rely on achieving high immunization coverage. *Contact tracing* - **Contact tracing** involves identifying and monitoring people who may have been exposed to an infected person to prevent further transmission. - While it is an essential **disease control measure** during outbreaks, it addresses individual chains of transmission rather than creating population-level immunity necessary for elimination. *Quarantine* - **Quarantine** involves separating and restricting the movement of apparently healthy people who may have been exposed to a contagious disease to see if they become sick. - While essential for **preventing disease spread** during an outbreak, it is a control measure and does not directly eliminate a disease from a population. *Isolation* - **Isolation** is the separation of sick people with a contagious disease from people who are not sick to prevent the spread of illness. - It is a crucial measure for **disease control** and management of active cases, but it does not achieve population-level immunity or directly lead to disease elimination.

Q: 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?

Common source continuous or repeated exposure epidemic. ***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.

Q: What is the overall most common cancer in the world?

Breast cancer. ***Breast cancer*** - **Breast cancer** is the most common cancer globally by incidence, with approximately **2.3 million new cases** diagnosed annually (GLOBOCAN 2020). - It surpassed lung cancer in 2020 to become the leading cancer worldwide, affecting both women (predominantly) and men. - High incidence is seen particularly in developed countries, though rates are rising globally. *Lung cancer* - **Lung cancer** is the **second most common cancer** globally by incidence but remains the **leading cause of cancer deaths** worldwide. - While it has high mortality due to late diagnosis and aggressive nature, its overall incidence is slightly lower than breast cancer. - Strongly associated with smoking and environmental pollutants. *Thyroid carcinoma* - **Thyroid carcinoma** has increasing incidence but is not among the top most common cancers globally. - It has excellent prognosis with early detection and treatment, predominantly affecting women but also occurring in men. - The increase in incidence is partly due to improved detection methods. *Colon cancer* - **Colon cancer** (colorectal cancer) is the third most common cancer globally but does not surpass breast cancer in overall incidence. - Its occurrence varies geographically and is strongly linked to lifestyle factors including diet, obesity, and physical inactivity.

Q: Epidemic marker of TB?

Sputum AFB positivity rate. ***Sputum AFB positivity rate*** - The **sputum acid-fast bacilli (AFB) positivity rate** directly indicates the number of individuals actively shedding viable *Mycobacterium tuberculosis* in their respiratory secretions. - This metric reflects the **infectious pool** within a community, making it a robust marker for assessing ongoing transmission and the epidemic status of tuberculosis. *Tuberculin test positivity rate* - The **tuberculin skin test (TST)** measures exposure to TB and latent infection, not active, infectious disease. - A high positivity rate indicates a high prevalence of **latent TB infection**, but doesn't differentiate between old exposure, cleared infection, or active disease, nor does it directly measure transmissibility. *Chest x-ray positivity rate* - **Chest X-rays** can identify pulmonary abnormalities consistent with TB, including active disease. - However, CXR findings are **non-specific** for TB and can be suggestive of previous infection or other lung conditions, making it less precise than sputum AFB for defining an active epidemic. *None of the options* - This option is incorrect because the **sputum AFB positivity rate** is a well-established and direct indicator of active TB disease transmission and epidemic activity.

Q: Sputum examination for AFB is a type of

Secondary prevention. ***Secondary prevention*** - **Sputum examination for AFB** (acid-fast bacilli) aims for **early diagnosis** and **prompt treatment** of tuberculosis. - This level of prevention focuses on **halting the progression of a disease** that has already occurred or reducing its severity. *Tertiary prevention* - This level of prevention involves **rehabilitation** and preventing complications in individuals with **established disease**. - Examples include physical therapy after a stroke or managing chronic conditions to improve quality of life. *Primordial prevention* - This stage of prevention focuses on **preventing the emergence of risk factors** in the first place, often by addressing broad socioeconomic and environmental determinants. - It targets the entire population and is concerned with **social and environmental conditions** that contribute to risk factors. *Primary prevention* - This level of prevention aims to **prevent the onset of disease** by reducing exposure to risk factors or increasing resistance to disease. - Examples include **vaccination**, health education, and promoting healthy lifestyles to **prevent initial disease occurrence**.

Q: Which disease is highly transmitted during the incubation period?

Measles. ***Measles*** - Measles is **highly transmissible during the late incubation period**, starting approximately **4 days before the rash appears**. - The incubation period is 10-14 days from exposure to rash onset, and viral shedding begins in the **last few days of incubation** even before symptoms develop. - Patients remain contagious through the **prodromal phase** (fever, cough, coryza, conjunctivitis) and up to 4 days after rash onset, making it one of the most contagious diseases with **significant pre-symptomatic transmission**. - This characteristic makes measles difficult to control as infected individuals unknowingly spread the virus before diagnosis. *Pertussis* - While pertussis is highly contagious, peak transmission occurs during the **catarrhal stage**, which is the **first clinical stage after incubation ends**, not during the incubation period itself. - The incubation period (7-10 days) is relatively **non-infectious**, with bacterial shedding peaking once symptoms (mild cold-like symptoms) appear. - Maximum contagiousness occurs during the catarrhal and early paroxysmal stages when symptoms are present. *Brucellosis* - **Brucellosis** is primarily transmitted through direct contact with infected animals or consumption of unpasteurized dairy products. - **Human-to-human transmission is extremely rare**, making transmission during the incubation period clinically insignificant. - It does not fit the pattern of respiratory droplet or direct person-to-person spread during incubation. *Cholera* - **Cholera** transmission occurs mainly through the **fecal-oral route** via contaminated water or food. - Maximum infectivity occurs during the **symptomatic phase** when large volumes of bacteria-laden stool are passed. - During the short incubation period (few hours to 5 days), bacterial shedding is minimal and transmission risk is low compared to the symptomatic phase.

Q: Transition from increased prevalence of infectious and communicable diseases to man-made diseases is known as

Epidemiological transition. ***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.

Q: Epidemic resulting from person to person transmission is known as:

Propagated epidemic.. ***Propagated epidemic*** - This type of epidemic is characterized by **person-to-person transmission**, resulting in a pattern of increasing cases over time until a significant portion of the susceptible population is infected or interventions are effective. - The epidemic curve typically shows **multiple waves** or peaks, reflecting successive generations of infection. - Classic examples include **measles, chickenpox, and influenza** outbreaks. *Point source epidemic* - A point source epidemic occurs when people are exposed to the **same source** over a **brief, limited period**. - The epidemic curve typically shows a **sharp upward slope** and a gradual downward slope, with cases clustering around a single incubation period. - Does not involve person-to-person transmission. *Common source epidemic* - This type of epidemic results from exposure to a **common noxious influence**, such as contaminated food or water, affecting multiple individuals. - Common source epidemics can be further classified as **point source** or **continuous/intermittent source** depending on the duration of exposure. - Does not primarily involve person-to-person transmission. *Mixed epidemic* - A mixed epidemic starts as a **common source outbreak** but is followed by **secondary person-to-person transmission**. - Shows characteristics of both common source and propagated epidemics in its epidemic curve. - Not the primary term for person-to-person transmission epidemics.

Question 1

Incubation period of Salmonella typhi -

Accepted Answer

3-21 days

Answer

2-5 days

Answer

14-25 days

Answer

0-60 days

Question 2

All of the following are true about the Herd immunity for infectious diseases except -

Accepted Answer

It is more easily achieved for infections that do not have a sub-clinical phase

Answer

In the case of tetanus it does not protect the individual

Answer

It is affected by the presence and distribution of alternative animal hosts

Answer

It refers to group protection beyond what is afforded by the protection of immunized individuals

Question 3

Disease elimination is helped by-

Accepted Answer

Herd immunity

Answer

Contact tracing

Answer

Quarantine

Answer

Isolation

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?

Accepted Answer

Common source continuous or repeated exposure epidemic

Answer

Propagated epidemic

Answer

Common source single exposure epidemic

Answer

Long term or secular trend epidemic

Question 5

What is the overall most common cancer in the world?

Accepted Answer

Breast cancer

Answer

Thyroid carcinoma

Answer

Lung cancer

Answer

Colon cancer

Question 6

Epidemic marker of TB?

Accepted Answer

Sputum AFB positivity rate

Answer

Tuberculin test positivity rate

Answer

Chest x-ray positivity rate

Answer

None of the options

Question 7

Sputum examination for AFB is a type of

Accepted Answer

Secondary prevention

Answer

Tertiary prevention

Answer

Primordial prevention

Answer

Primary prevention

Question 8

Which disease is highly transmitted during the incubation period?

Accepted Answer

Measles

Answer

Pertussis

Answer

Brucellosis

Answer

Cholera

Question 9

Transition from increased prevalence of infectious and communicable diseases to man-made diseases is known as

Accepted Answer

Epidemiological transition

Answer

Demographic transition

Answer

Paradoxical transition

Answer

Reversal of transition

Question 10

Epidemic resulting from person to person transmission is known as:

Accepted Answer

Propagated epidemic.

Answer

Point source epidemic.

Answer

Common source epidemic.

Answer

Mixed epidemic.

Epidemiology — MCQs

Epidemiology — MCQs

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