Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 691: Gap in the time interval between the onset of the primary and secondary case is

A. Serial interval (Correct Answer)
B. Generation time
C. Onset period
D. Incubation period

Explanation: ***Serial interval*** - The **serial interval** directly measures the time elapsed between the onset of symptoms in a primary case and the onset of symptoms in a secondary case infected by the primary case. - This metric is crucial for understanding the **speed of pathogen transmission** within a population. *Generation time* - **Generation time** refers to the period between infection in a primary case and infection in a secondary case, which is difficult to observe directly. - While related to the serial interval, it specifically focuses on **infection events** rather than symptom onset. *Onset period* - **Onset period** is not a standard epidemiological term for the time gap between primary and secondary cases. - It might vaguely refer to the time from exposure to symptom onset but lacks the specific context of **transmission dynamics**. *Incubation period* - The **incubation period** is the time between exposure to an infectious agent and the onset of symptoms in a single individual. - It does not involve the **transmission event** between a primary and a secondary case.

Question 692: 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 693: What is the primary effect of pyrethrum on mosquitoes?

A. Contact
B. Knock down (Correct Answer)
C. Residual
D. Repellent

Explanation: ***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.

Question 694: What is the most common source of infection for whooping cough?

A. Chronic carrier
B. Acute carrier
C. Case (Correct Answer)
D. Recovering carrier

Explanation: ***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

Question 695: On the SAFE strategy, which option is NOT part of the approach?

A. Screening (Correct Answer)
B. Facial hygiene
C. Environmental modification
D. Antibiotics

Explanation: ***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.

Question 696: Which of the following statements regarding dengue fever is false?

A. Common in south Asian region
B. Transmitted by Aedes aegypti
C. Thrombocytopenia
D. Subclinical cases never occur (Correct Answer)

Explanation: **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**.

Question 697: What is the primary reason leprosy has not been eradicated?

A. Limited animal reservoirs
B. Social stigma and delayed diagnosis (Correct Answer)
C. Long incubation period
D. Lack of an effective vaccine

Explanation: ***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.

Question 698: Strategies for prevention of Neonatal Tetanus include all of the following except -

A. 2 doses of TT to all pregnant women
B. Giving penicillin to all the newborns (Correct Answer)
C. Immunizing all married women
D. 5 clean practices

Explanation: ***Giving penicillin to all the newborns*** - This is not a recommended strategy for preventing neonatal tetanus. While **penicillin** can treat bacterial infections, it does not prevent neonatal tetanus, which is caused by the toxin produced by *Clostridium tetani*, not the bacterium itself. - The primary prevention of neonatal tetanus focuses on **maternal immunization** and **aseptic delivery practices**, not routine antibiotic prophylaxis for newborns. *5 clean practices* - The "5 cleans" refers to **clean hands**, **clean surface**, **clean cord cutting instrument**, **clean cord tie**, and **clean perineum**. These practices significantly reduce the risk of cord contamination by *Clostridium tetani* spores. - Implementing these practices during delivery and cord care is a crucial and **effective strategy** for preventing neonatal tetanus. *2 doses of TT to all pregnant women* - Administering two doses of **tetanus toxoid (TT) vaccine** to pregnant women provides **active immunity** to the mother, who then transfers protective **maternal antibodies** transplacentally to the newborn, providing **passive immunity** to the infant. - This maternal immunization protects the infant during the vulnerable neonatal period by neutralizing the tetanus toxin. *Immunizing all married women* - Immunizing all married women of childbearing age with **tetanus toxoid** ensures that they are protected against tetanus and can pass on protective antibodies to their future offspring. - This is a broader public health strategy aimed at **eliminating maternal and neonatal tetanus** by ensuring robust population immunity.

Question 699: Spread of chickenpox is maximum when?

A. After formation of scab
B. Just before and after onset of rash (Correct Answer)
C. One week before onset of rash
D. During convalescence

Explanation: ***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.

Question 700: Case finding in the Revised National Tuberculosis Control Programme (RNTCP), now known as the National Tuberculosis Elimination Programme (NTEP), is based on which of the following diagnostic methods?

A. Mantoux test
B. Chest X-ray
C. Sputum culture
D. Sputum microscopy (Correct Answer)

Explanation: ***Sputum microscopy*** - The **National Tuberculosis Elimination Programme (NTEP)**, formerly known as the **Revised National Tuberculosis Control Programme (RNTCP)**, primarily relies on **sputum smear microscopy** for case finding of pulmonary TB due to its cost-effectiveness, speed, and widespread availability in resource-limited settings. - It identifies individuals who are **smear-positive**, meaning they are actively shedding bacteria and are highly infectious. - Sputum microscopy remains the **cornerstone of case finding** in the program despite the availability of newer diagnostic methods. *Mantoux test* - The **Mantoux test** (Tuberculin Skin Test) is used to detect **TB infection**, not active TB disease, and does not differentiate between latent infection and active disease. - It is not used for primary case finding in NTEP due to its limitations in specificity and sensitivity, especially in BCG-vaccinated populations. *Chest X-ray* - **Chest X-ray** is a valuable diagnostic tool for active TB, but it is typically used as a **supplementary investigation** or for screening specific populations, not as the primary diagnostic method for routine case finding in NTEP. - Its use requires specialized equipment and trained personnel, making it less feasible for widespread primary screening compared to sputum microscopy. *Sputum culture* - **Sputum culture** is the **gold standard** for TB diagnosis and drug susceptibility testing, offering higher sensitivity than microscopy. - However, it is more expensive, takes several weeks to yield results, and requires specialized laboratory facilities, making it impractical as the primary method for routine case finding and initial diagnosis in the NTEP.

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