Infectious Diseases Practice Questions

Q: A patient with cough was sputum AFB negative but chest X-ray was suggestive of TB. What should be the next step according to RNTCP?

Nucleic acid amplification test. Nucleic acid amplification test - According to the and Revised National Tuberculosis Control Program (RNTCP) guidelines, if sputum AFB microscopy is negative but clinical suspicion and chest X-ray point towards TB, NAAT (Nucleic Acid Amplification Test) is recommended as the next confirmatory step [1]. - NAATs like CBNAAT (Cartridge-Based Nucleic Acid Amplification Test) or TrueNat provide rapid detection of Mycobacterium tuberculosis and resistance to Rifampicin, aiding in early diagnosis and appropriate treatment initiation. Tuberculin test - The Tuberculin Skin Test (TST), also known as the Mantoux test, indicates past exposure to TB or latent infection, but it cannot differentiate between active disease, latent infection, or past treated infection [2]. - A positive TST in an adult with a suggestive chest X-ray still requires further investigation for active disease, as it does not confirm active pulmonary TB [2]. Line probe assay - Line Probe Assay (LPA) is a molecular test used for rapid detection of MDR-TB (multi-drug resistant TB) by identifying mutations associated with resistance to Rifampicin and Isoniazid. - While useful for resistance testing, it typically requires a positive culture or direct sputum sample with a higher bacterial load and is not the primary diagnostic test for initial confirmation of TB when sputum AFB is negative. Culture - Mycobacterial culture is the gold standard for TB diagnosis, providing definitive confirmation and enabling drug susceptibility testing (DST) [1]. - However, culture results can take several weeks (typically 3-6 weeks), which delays treatment initiation, making it a less immediate next step compared to rapid molecular tests like NAAT in cases of strong clinical suspicion.

Q: Isolation period of Hepatitis A after the onset of jaundice is:

1 week. ***1 week*** - Individuals with **Hepatitis A** are considered infectious for about **1 week** after the onset of **jaundice** or within 2 weeks of symptom onset. - This period is critical for implementing preventive measures like **handwashing** to prevent further spread. *4 weeks* - While viral shedding can occur for several weeks, the period of highest infectivity and public health concern typically extends for **1 week** post-jaundice. - Extending isolation to 4 weeks might be overly restrictive without a significant additional public health benefit in most cases. *3 weeks* - The peak period of **viral shedding** and infectivity for Hepatitis A generally occurs before and within the first week of jaundice. - By the third week post-jaundice, viral shedding has usually significantly decreased, making the individual much less infectious. *2 weeks* - Although some viral shedding can still occur, the most critical period for transmissibility has largely passed by the end of the **first week** after jaundice onset. - Most public health guidelines focus on measures during the period of highest risk to prevent widespread transmission.

Q: Screening age for trachoma is:

1-9 years. ***1-9 years*** - The **WHO recommends mass drug administration (MDA) for trachoma control** focused on communities where the prevalence of trachomatous inflammation—follicular (TF) in children aged **1–9 years** is 5% or more. - This age group is considered the **primary reservoir of infection** and crucial for transmission dynamics, making it the most appropriate target for screening and intervention. *9-14 years* - While older children can be infected, the **highest prevalence of active trachoma (TF and TI)** is typically found in younger children, making this age group less significant for initial screening compared to 1-9 years. - Screening this age group alone might miss a substantial portion of the **infectious reservoir**, limiting the effectiveness of control programs. *Below 5 years school child only* - This option is too restrictive as **trachoma also affects non-school-going children** and those slightly older than 5, but still within the 1-9 year primary target range. - **Excluding children in the 5-9 year group** would significantly reduce the impact of screening efforts, as younger school-age and pre-school children are highly susceptible. *5-15 years* - This age range is broader than the recommended primary screening age group and would include those for whom **active infection prevalence begins to decline**. - Focusing on a *broader and older* group might dilute resources that are most effectively used in the **1-9 year-old group**, where intervention has the greatest impact on transmission.

Q: Most efficient larval control method to prevent transmission of urban malaria:

Filling of ditches and cesspools. ***Filling of ditches and cesspools*** - This method eliminates **breeding sites** for mosquito larvae by removing stagnant water collections - Effective for **environmental source reduction**, a fundamental principle of larval control - Addresses both rural and urban malaria vector breeding sites including **Anopheles stephensi** in urban areas - Direct intervention at the **larval stage** prevents adult mosquito emergence *Cleaning of drains* - Important for sanitation and can reduce breeding sites for both **Anopheles stephensi** (urban malaria) and **Aedes** (dengue) in urban settings - However, drains are continuously replenished with water, making this less efficient as a long-term larval control measure - Requires frequent repetition to maintain effectiveness *Covering overhead tanks* - Highly effective for preventing **Anopheles stephensi** breeding in stored water, which is a significant source of urban malaria transmission - However, this is a **preventive measure** rather than an active larval control method - Does not eliminate existing larvae, only prevents new breeding *Uprooting of plants* - Reduces adult mosquito **resting sites** but does not directly address the **larval stage** - Not a larval control method and therefore not effective for preventing malaria transmission at the source

Q: Animal reservoir is seen in all except -

Measles. ***Measles*** - Measles is a **human-specific disease** and does not have an animal reservoir. - The virus is spread person-to-person through **respiratory droplets**. *Yellow fever* - **Monkeys** are the primary animal reservoir for yellow fever, particularly in jungle cycles. - The virus is transmitted to humans by **mosquitoes** that have fed on infected monkeys. *Influenza* - Various **animal species**, such as birds (especially wild waterfowl) and pigs, serve as reservoirs for influenza viruses. - These animal reservoirs contribute to the emergence of **new human influenza strains** through antigenic shift and drift. *Rabies* - Rabies is a **zoonotic disease** with a significant animal reservoir, predominantly in wild carnivores like raccoons, bats, foxes, and skunks. - Transmission to humans primarily occurs through the bite of an **infected animal**.

Q: Quarantine period of yellow fever is

6 days. ***6 days*** - The **quarantine period** for yellow fever is **6 days**, which corresponds to the maximum incubation period of the virus. - This is the standard quarantine duration recommended in **Park's Preventive and Social Medicine** and **IAPSM textbooks**. - The quarantine period ensures that exposed individuals are monitored through the complete incubation period before they could potentially develop symptoms and transmit the disease. - Yellow fever has an incubation period of **3-6 days**, and the quarantine period is set at the upper limit to ensure public health safety. *8 days* - While some international sources may cite slightly longer periods, **8 days** is not the standard quarantine period for yellow fever in Indian medical education. - This duration exceeds the recognized incubation period and is not aligned with standard public health practice for yellow fever. *10 days* - A **10-day quarantine period** is excessively long for yellow fever. - This would be more appropriate for diseases with longer incubation periods. - Does not align with the known viral kinetics of yellow fever virus. *9 days* - **9 days** is not the officially recognized quarantine period for yellow fever. - This period falls outside the established guidelines in standard Indian medical textbooks for managing yellow fever exposure.

Q: In tuberculosis, a 'case' is

Sputum positive. ***Sputum positive*** - In the context of **tuberculosis (TB)**, a 'case' is defined by **bacteriological confirmation**, most commonly through **sputum smear positivity** for acid-fast bacilli (AFB). - According to **RNTCP (Revised National Tuberculosis Control Programme)** guidelines, a sputum smear-positive case is one with at least **two sputum specimens positive for AFB**, or one sputum specimen positive for AFB plus radiographic abnormalities consistent with active pulmonary TB. - A positive sputum smear confirms the presence of **Mycobacterium tuberculosis** in the respiratory tract, indicating active, transmissible infection requiring immediate treatment. *Cough* - **Cough** is a common symptom of tuberculosis but is not sufficient on its own to define a 'case'. - Many respiratory conditions can cause a cough, and it does not confirm the presence of **Mycobacterium tuberculosis** or infectiousness. - Cough lasting more than 2-3 weeks is a screening criterion for TB suspects, not a case definition. *X-ray positive* - A **positive chest X-ray** can show abnormalities consistent with tuberculosis, such as infiltrates, cavities, or hilar lymphadenopathy. - However, radiological findings alone do not definitively confirm a TB diagnosis, as many other conditions can mimic TB on chest X-ray. - Chest X-ray is used for **clinically diagnosed TB cases** when bacteriological confirmation is not possible, but it does not establish active infectivity without microbiological confirmation. *Mantoux positive* - A **positive Mantoux test** (tuberculin skin test) indicates exposure to Mycobacterium tuberculosis and the presence of a cell-mediated immune response. - It signifies **latent TB infection (LTBI)** but does not indicate active, infectious disease. - Many people with positive Mantoux tests never develop active TB and are not considered 'cases'.

Q: Which of the following is a vector for Dengue fever?

Aedes aegypti. ***Aedes aegypti*** - The **Aedes aegypti** mosquito is the primary vector responsible for transmitting the **Dengue virus** to humans. - It is an urban mosquito that breeds in and around human dwellings in small collections of fresh water. *Culex* - **Culex mosquitoes** are known vectors for diseases like **West Nile virus**, Japanese encephalitis, and filariasis, but not Dengue fever. - They typically bite at night and prefer to breed in polluted water sources. *Mansonia* - **Mansonia mosquitoes** are vectors for diseases such as **lymphatic filariasis** and other arboviruses, but they are not associated with Dengue transmission. - These mosquitoes often breed in water bodies containing aquatic plants, to which their larvae attach for oxygen. *Anopheles* - **Anopheles mosquitoes** are the well-known vectors for **malaria**, transmitting **Plasmodium parasites**. - While they can transmit other arboviruses, they are not involved in the transmission cycle of Dengue fever.

Q: Isolation as a method of control is used for infection in which of the following diseases?

All of the options. ***All of the options*** - **Isolation is a critical public health measure** used to prevent the spread of contagious diseases by separating infected individuals from susceptible populations. - All three diseases listed—**Plague, Mumps, and Diphtheria**—require isolation as an essential control measure due to their communicable nature. **Why each disease requires isolation:** **Plague:** - **Pneumonic plague** is highly contagious through respiratory droplets and requires **strict isolation** until 48-72 hours of appropriate antibiotic therapy. - **Bubonic plague** requires standard precautions with isolation to prevent secondary pneumonic spread. - Due to high mortality and epidemic potential, isolation is mandatory. **Mumps:** - A **highly contagious viral infection** spread through respiratory droplets and direct contact with saliva. - **Isolation for 5 days** from the onset of parotid swelling is recommended by CDC and IAP guidelines. - Prevents transmission in schools, colleges, and healthcare settings. **Diphtheria:** - A serious **bacterial infection** spread through respiratory droplets and direct contact. - **Strict isolation** is required until two consecutive throat/nose swabs (taken 24 hours apart) are culture-negative, typically after 14 days of appropriate antibiotic therapy. - Essential to prevent outbreaks due to toxin-mediated complications and high case-fatality rate. *Why not individual options?* - Since isolation is used as a control measure for **all three diseases**, the most accurate answer is "All of the options." - Each disease individually would be incomplete as an answer.

Q: Mosquitoes whose eggs are found attached to aquatic plants are

Mansonia. ***Mansonia*** - *Mansonia* mosquitoes are unique in that their **eggs are laid individually and attached to the undersurface of floating aquatic plants**. - The larvae and pupae also attach to these plants using specialized siphons to obtain oxygen, instead of rising to the water surface. *Culex* - *Culex* mosquitoes lay their **eggs in rafts on the surface of still water**, not attached to aquatic plants. - The larvae and pupae are free-swimming and obtain oxygen directly from the water surface. *Aedes* - *Aedes* mosquitoes typically lay **single eggs on moist surfaces just above the water line** in containers or tree holes, which hatch when flooded. - Their eggs are not attached to aquatic plants in the water. *Anopheles* - *Anopheles* mosquitoes lay **single, boat-shaped eggs directly on the water surface**, each with floats on either side. - These eggs are not attached to aquatic plants and float freely on the water.

Question 1

A patient with cough was sputum AFB negative but chest X-ray was suggestive of TB. What should be the next step according to RNTCP?

Accepted Answer

Nucleic acid amplification test

Answer

Tuberculin test

Answer

Line probe assay

Answer

Culture

Question 2

Isolation period of Hepatitis A after the onset of jaundice is:

Accepted Answer

1 week

Answer

4 weeks

Answer

3 weeks

Answer

2 weeks

Question 3

Screening age for trachoma is:

Accepted Answer

1-9 years

Answer

9-14 years

Answer

Below 5 years school child only

Answer

5-15 years

Question 4

Most efficient larval control method to prevent transmission of urban malaria:

Accepted Answer

Filling of ditches and cesspools

Answer

Cleaning of drains

Answer

Covering overhead tanks

Answer

Uprooting of plants

Question 5

Animal reservoir is seen in all except -

Accepted Answer

Measles

Answer

Yellow fever

Answer

Influenza

Answer

Rabies

Question 6

Quarantine period of yellow fever is

Accepted Answer

6 days

Answer

10 days

Answer

8 days

Answer

9 days

Question 7

In tuberculosis, a 'case' is

Accepted Answer

Sputum positive

Answer

Cough

Answer

X-ray positive

Answer

Mantoux positive

Question 8

Which of the following is a vector for Dengue fever?

Accepted Answer

Aedes aegypti

Answer

Culex

Answer

Mansonia

Answer

Anopheles

Question 9

Isolation as a method of control is used for infection in which of the following diseases?

Accepted Answer

All of the options

Answer

Plague

Answer

Mumps

Answer

Diphtheria

Question 10

Mosquitoes whose eggs are found attached to aquatic plants are

Accepted Answer

Mansonia

Answer

Culex

Answer

Aedes

Answer

Anopheles

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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