Infectious Diseases Practice Questions

Q: Which of the following diseases is primarily transmitted by body lice?

Trench fever. ***Trench fever*** - **Trench fever** is caused by the bacterium *Bartonella quintana* and is classically transmitted by the **body louse** acquiring the bacteria from an infected human. - The disease is characterized by relapsing fevers, bone pain (especially in the shins), headache, and rash, and it gained prominence during World War I due to poor hygiene and louse infestations among soldiers. *Plague* - **Plague**, caused by *Yersinia pestis*, is primarily transmitted by the bite of infected **fleas**, usually from rodents to humans. - While human-to-human transmission can occur in pneumonic plague, lice are not the primary vector for bubonic or septicemic forms. *Endemic typhus* - **Endemic (murine) typhus** is caused by *Rickettsia typhi* and is transmitted by the **rat flea** (*Xenopsylla cheopis*), not body lice. - It occurs primarily in areas with rodents and their fleas, typically presenting with fever, headache, and a rash. *Chiggerosis* - **Chiggerosis** (also known as trombiculiasis or scrub itch) is caused by the bite of **chigger mites** (larval mites of the family Trombiculidae), which burrow into the skin. - These mites are not body lice and do not transmit bacterial infections like trench fever; their bites cause intensely itchy papules.

Q: Which of the following diseases requires airborne isolation with negative pressure rooms for the longest duration during active infection?

Tuberculosis. ***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.

Q: What is the primary effect of pyrethrum on mosquitoes?

Knock down. ***Knock down*** - **Pyrethrum's** primary effect is rapid **knockdown**—swiftly paralyzing and felling mosquitoes within minutes of exposure. - While many insects recover later, this immediate effect reduces biting and disease transmission effectively during short-term exposure. *Residual* - This effect refers to the ability of an insecticide to remain active on a surface for an extended period, providing control long after application. - **Pyrethrum** has poor residual activity as it rapidly degrades in light and air, making it less effective for long-term surface treatment. *Repellent* - A repellent discourages insects from approaching or landing, typically through olfactory or tactile cues. - While some **pyrethrin** compounds might have slight repellent properties at low concentrations, this is not their primary or most significant effect. *Contact* - This term describes how an insecticide affects an insect upon direct physical touch. - While **pyrethrum** is indeed a contact insecticide, "contact" simply describes the mode of entry, whereas "**knockdown**" specifically describes the *primary acute effect* of that contact.

Q: On the SAFE strategy, which option is NOT part of the approach?

Screening. ***Screening*** - The **SAFE strategy** is a public health intervention for **trachoma control**, consisting of **Surgery for trichiasis**, **Antibiotics for chlamydial infection**, **Facial hygiene**, and **Environmental improvement**. - **Screening** for trachoma, while a critical diagnostic step, is not one of the four core components used in the acronym itself. *Antibiotics* - This component involves the mass administration of **azithromycin** within communities to treat active chlamydial infections and reduce the transmission of trachoma. - It targets the **infection-causing bacterium**, *Chlamydia trachomatis*. *Facial hygiene* - This part of the strategy promotes regular **face washing** to reduce the presence of ocular discharges and secretions, which are a major factor in the spread of *Chlamydia trachomatis* by flies and direct contact. - Improved facial hygiene helps to decrease the **transmission of the infection**. *Environmental modification* - This component refers to improving access to clean water and sanitation facilities, such as latrines. - Better sanitation reduces **fly breeding sites** and the transmission of the bacteria that cause trachoma.

Q: Which of the following is the primary epidemiological indicator for malaria?

Annual parasite incidence. ***Annual parasite incidence*** - **Annual parasite incidence (API)** refers to the number of confirmed malaria cases per 1,000 population per year in a given area. - It is a **key epidemiological indicator** used to assess the burden of malaria and track trends over time, providing a direct measure of disease occurrence. *Annual falciparum incidence* - This indicator focuses specifically on **_Plasmodium falciparum_ infections**, which are often the most severe form of malaria. - While important, it does not encompass all malaria species and therefore provides a less comprehensive measure of the overall malaria burden compared to API. *Annual blood examination rate* - The **annual blood examination rate (ABER)** indicates the number of blood slides examined for malaria per 1,000 population per year. - It is a measure of **surveillance effort** and access to diagnostic testing, rather than a direct measure of malaria incidence. *Annual incidence of malaria cases* - While this phrase describes generally what an epidemiological indicator for malaria would measure, it is less specific and a less commonly used standardized term than **Annual Parasite Incidence (API)**. - The term **API** is universally recognized and has a precise definition related to confirmed parasite-positive cases per 1,000 population.

Q: What is the most common source of infection for whooping cough?

Case. ***Correct Option: Case*** - A **case** refers to an individual currently experiencing symptoms of whooping cough and actively shedding *Bordetella pertussis*, making them the primary source of transmission - The highest period of contagiousness occurs during the **catarrhal and early paroxysmal stages** when the patient is symptomatic - Direct contact with symptomatic cases through respiratory droplets is the most common mode of transmission for pertussis *Incorrect: Chronic carrier* - *Bordetella pertussis* **does not establish a chronic carrier state** in humans - Unlike diseases such as typhoid or hepatitis B, pertussis requires active infection for transmission *Incorrect: Acute carrier* - While individuals during the incubation period may carry bacteria, their transmission efficiency is significantly lower than symptomatic cases - The term "acute carrier" is not the standard epidemiological terminology for the primary source of pertussis transmission *Incorrect: Recovering carrier* - Recovering individuals (convalescent phase) have markedly **reduced bacterial shedding** compared to active cases - While some transmission may occur during recovery, it is far less common than from symptomatic individuals - The period of highest contagiousness correlates with the symptomatic phase, not the recovery phase

Q: Which of the following statements regarding dengue fever is false?

Subclinical cases never occur. **Subclinical cases never occur** - This statement is false because **subclinical** or **asymptomatic infections** are common in dengue fever, meaning many infected individuals do not develop noticeable symptoms but can still transmit the virus. - Studies indicate that the ratio of asymptomatic to symptomatic cases can be as high as 4:1, playing a significant role in **virus transmission** and **herd immunity**. *Common in south Asian region* - This statement is true; **dengue fever** is highly **endemic** in South Asian regions, including countries like India, Bangladesh, and Pakistan, due to suitable climatic conditions for the **Aedes mosquito** and high population density. - The region experiences annual outbreaks, particularly during **monsoon seasons**, leading to a substantial public health burden. *Transmitted by Aedes aegypti* - This statement is true. Dengue fever is primarily transmitted to humans through the bite of infected female **Aedes aegypti mosquitoes**. - **Aedes albopictus** can also act as a vector, but **Aedes aegypti** is considered the main vector in most urban areas. *Thrombocytopenia* - This statement is true. **Thrombocytopenia** (low platelet count) is a hallmark of dengue fever, often correlating with disease severity and risk of **hemorrhage**. - As platelet counts drop, patients are at higher risk of **bleeding complications**, especially in **severe dengue**.

Q: What is the primary reason leprosy has not been eradicated?

Social stigma and delayed diagnosis. ***Social stigma and delayed diagnosis*** - **Social stigma** associated with leprosy often leads to patients hiding the disease, delaying presentation for diagnosis and treatment. - **Delayed diagnosis** results in continued transmission within communities and can lead to irreversible disabilities, making eradication difficult despite effective treatment. *Lack of an effective vaccine* - While a widely effective vaccine against leprosy is not available, the existing **BCG vaccine** offers some protection. - The primary barrier to eradication is not the absence of a vaccine, but rather the challenges in identifying and treating existing cases due to other factors. *Long incubation period* - The **long incubation period** (average 3-5 years) does make tracing contacts and preventing transmission challenging. - However, this alone does not outweigh the impact of late diagnosis and treatment in maintaining the disease's presence. *Limited animal reservoirs* - **Animal reservoirs** (e.g., armadillos in some regions) play a minor role in human transmission globally. - The vast majority of new cases arise from human-to-human transmission, making human factors more critical for perpetuating the disease.

Q: Spread of chickenpox is maximum when?

Just before and after onset of rash. ***Just before and after onset of rash*** - The period of maximum infectivity for chickenpox (varicella) is typically 1-2 days **before the onset of the rash** and continues for 4-5 days after the rash appears, or until all lesions have crusted over. - During this time, the **varicella-zoster virus** is actively replicating and shedding from the respiratory tract and skin lesions, making it highly transmissible. *After formation of scab* - Once all lesions have dried and **formed scabs**, the individual is generally no longer considered contagious. - The virus is no longer actively shed from crusted lesions, significantly reducing the risk of transmission. *One week before onset of rash* - While there might be some viral shedding during the **incubation period**, significant contagiousness usually begins closer to the rash onset (1-2 days prior). - A full week before the rash, viral replication might be occurring, but the quantity of shed virus is typically too low to cause widespread transmission. *During convalescence* - **Convalescence** refers to the period of recovery after the acute illness, which begins once all lesions have scabbed over. - During this stage, the individual is usually no longer infectious, as the active viral shedding has ceased.

Q: What is the diagnostic criterion for sputum-positive tuberculosis (TB)?

At least 1 sputum sample positive for AFB. The definition of sputum-positive TB, particularly in initial diagnosis, generally requires at least one **acid-fast bacilli (AFB) smear-positive** sputum sample [1]. This criterion is crucial for guiding initial treatment strategies and public health interventions for **infectious TB** [1]. While a BACTEC-positive result confirms the presence of **Mycobacterium tuberculosis**, a rapid AFB smear positive result is often the initial criterion for "sputum-positive" classification for immediate management [2]. While some guidelines or clinical contexts might emphasize multiple positive samples for confirmation, the widely accepted minimum for sputum-positive TB is **at least one positive AFB smear** [1].

Question 1

Which of the following diseases is primarily transmitted by body lice?

Accepted Answer

Trench fever

Answer

Plague

Answer

Endemic typhus

Answer

Chiggerosis

Question 2

Which of the following diseases requires airborne isolation with negative pressure rooms for the longest duration during active infection?

Accepted Answer

Tuberculosis

Answer

Cholera (severe cases)

Answer

Measles (during outbreaks)

Answer

Influenza

Question 3

What is the primary effect of pyrethrum on mosquitoes?

Accepted Answer

Knock down

Answer

Contact

Answer

Residual

Answer

Repellent

Question 4

On the SAFE strategy, which option is NOT part of the approach?

Accepted Answer

Screening

Answer

Facial hygiene

Answer

Environmental modification

Answer

Antibiotics

Question 5

Which of the following is the primary epidemiological indicator for malaria?

Accepted Answer

Annual parasite incidence

Answer

Annual falciparum incidence

Answer

Annual blood examination rate

Answer

Annual incidence of malaria cases

Question 6

What is the most common source of infection for whooping cough?

Accepted Answer

Case

Answer

Chronic carrier

Answer

Acute carrier

Answer

Recovering carrier

Question 7

Which of the following statements regarding dengue fever is false?

Accepted Answer

Subclinical cases never occur

Answer

Common in south Asian region

Answer

Transmitted by Aedes aegypti

Answer

Thrombocytopenia

Question 8

What is the primary reason leprosy has not been eradicated?

Accepted Answer

Social stigma and delayed diagnosis

Answer

Limited animal reservoirs

Answer

Long incubation period

Answer

Lack of an effective vaccine

Question 9

Spread of chickenpox is maximum when?

Accepted Answer

Just before and after onset of rash

Answer

After formation of scab

Answer

One week before onset of rash

Answer

During convalescence

Question 10

What is the diagnostic criterion for sputum-positive tuberculosis (TB)?

Accepted Answer

At least 1 sputum sample positive for AFB

Answer

BACTEC positive

Answer

No positive samples

Answer

2 out of 3 sputum samples positive

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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