Infectious Diseases Practice Questions

Q: The definition of extensively drug-resistant TB includes resistance to all of the following drugs, EXCEPT:

Ethambutol. **Explanation:** The definition of **Extensively Drug-Resistant Tuberculosis (XDR-TB)** was updated by the WHO in 2021 to reflect changes in treatment regimens. According to the current definition, XDR-TB is TB caused by *Mycobacterium tuberculosis* strains that fulfill the following criteria: 1. **MDR-TB/RR-TB:** Resistance to **Rifampicin** (with or without resistance to **Isoniazid**). 2. **Resistance to any Fluoroquinolone** (e.g., Levofloxacin or Moxifloxacin). 3. **Resistance to at least one additional Group A drug:** This includes **Bedaquiline** or **Linezolid**. **Why Ethambutol is the correct answer:** Ethambutol is a first-line antitubercular drug. While it is often part of the background resistance profile in MDR/XDR cases, its resistance is **not** a defining criterion for the classification of XDR-TB. **Analysis of Incorrect Options:** * **Rifampicin & Isoniazid (Options A & C):** Resistance to these two drugs defines Multi-Drug Resistant TB (MDR-TB). Since XDR-TB is a more severe form of MDR-TB, resistance to these (specifically Rifampicin) is a mandatory prerequisite. * **Amikacin (Option D):** Under the **older (pre-2021) WHO definition**, XDR-TB was defined as MDR-TB plus resistance to any fluoroquinolone and at least one of the three second-line injectable drugs (Amikacin, Capreomycin, or Kanamycin). While no longer a primary defining criterion in the 2021 update, it was historically a core component of the definition. **High-Yield Clinical Pearls for NEET-PG:** * **MDR-TB:** Resistance to at least Isoniazid (H) and Rifampicin (R). * **Pre-XDR-TB:** MDR-TB plus resistance to any Fluoroquinolone. * **Group A Drugs (WHO 2019):** Levofloxacin/Moxifloxacin, Bedaquiline, and Linezolid. These are now the most potent drugs for drug-resistant TB. * **True XDR (2021 Update):** MDR + Fluoroquinolone resistance + (Bedaquiline OR Linezolid) resistance.

Q: Which of the following is NOT true of Kyasanur Forest Disease?

Caused by a retrovirus. **Kyasanur Forest Disease (KFD)**, commonly known as "Monkey Fever," is a viral hemorrhagic fever endemic to the Western Ghats of India. **Explanation of the Correct Answer:** * **Option B (Incorrect Statement):** KFD is **not** caused by a retrovirus. It is caused by the **Kyasanur Forest Disease Virus (KFDV)**, which belongs to the family **Flaviviridae** and the genus *Flavivirus*. It is a single-stranded RNA virus. **Analysis of Other Options:** * **Option A (Incorrect Statement in Question):** This is actually the **incorrect statement** regarding the vector. KFD is transmitted by **Hard Ticks** (*Haemaphysalis spinigera*), not soft ticks. However, in the context of this specific MCQ format where "Retrovirus" is marked as the primary key, it highlights that KFDV is a Flavivirus. (Note: In many exams, both A and B could be considered technically false, but B is a fundamental virological error). * **Option C (True):** The incubation period is typically **3 to 8 days**. The disease often presents with a sudden onset of high-grade fever, headache, and severe myalgia, sometimes followed by a biphasic illness involving neurological symptoms. * **Option D (True):** A **formalin-inactivated (killed) vaccine** is available and used in endemic areas of Karnataka. It requires two primary doses (1 month apart) and periodic boosters. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** Monkeys (*Black-faced Langur* and *Bonnet Macaque*) are the common hosts; their death is often an early warning sign of an outbreak. * **Vector:** *Haemaphysalis spinigera* (Hard tick). * **Diagnosis:** PCR (early phase) or IgM ELISA. * **Distribution:** First isolated in 1957 from the Kyasanur Forest in Shimoga district, Karnataka. * **Seasonality:** Peak incidence occurs during the dry season (January–June) when human activity in forests increases.

Q: What is the time gap between the appearance of Koplik's spots and the cutaneous rash in measles?

3-4 days. **Explanation:** Measles (Rubeola) follows a distinct chronological progression of clinical features. The correct answer is **3-4 days** because of the specific timing of the prodromal and eruptive phases. 1. **Why Option B is correct:** Measles has a prodromal stage characterized by the "3 Cs" (Cough, Coryza, Conjunctivitis) and fever. **Koplik’s spots**—the pathognomonic enanthem—typically appear on the buccal mucosa opposite the lower second molars about **2 days before** the rash. The characteristic maculopapular rash (exanthem) usually appears on the **4th day** of the fever. Therefore, the interval between the appearance of Koplik’s spots and the cutaneous rash is approximately **2 to 4 days** (averaging 3-4 days). 2. **Why other options are incorrect:** * **Option A (24 hours):** This is too short; Koplik's spots usually precede the rash by at least 48 hours. * **Option C (2 weeks):** This is the approximate incubation period of Measles (10–14 days), not the interval between clinical signs. * **Option D (10 days):** This is the time from exposure to the onset of the first symptom (fever), not the gap between the spots and the rash. **High-Yield Clinical Pearls for NEET-PG:** * **Koplik’s Spots:** Described as "grains of salt on a red background." They disappear within 24–48 hours after the rash appears. * **Rash Progression:** Starts behind the ears (retro-auricular), spreads to the face/neck, then downwards to the trunk and limbs (cephalocaudal progression). * **Infectivity:** A patient is infectious from **4 days before to 4 days after** the appearance of the rash. * **Vitamin A:** Supplementation is recommended for all children with measles to prevent complications like blindness and pneumonia.

Q: In RNTCP, what is the schedule for sputum examination after beginning chemotherapy in Category I patients?

2, 4, and 6 months. **Explanation:** Under the **Revised National Tuberculosis Control Programme (RNTCP)**—now transitioned into the National TB Elimination Programme (NTEP)—monitoring treatment response through sputum smear microscopy is a critical component of the DOTS strategy. **1. Why 2, 4, and 6 months is correct:** For **Category I patients** (New cases), the standard treatment duration is 6 months (2 months of Intensive Phase and 4 months of Continuation Phase). Sputum examinations are scheduled at specific milestones to assess bacterial clearance: * **At 2 months:** To check for "Sputum Conversion" at the end of the Intensive Phase (IP). If positive, the IP is no longer extended (as per newer guidelines), but the patient moves to the Continuation Phase (CP) with close monitoring. * **At 4 months:** To monitor progress during the CP. * **At 6 months:** To confirm "Cure" at the end of treatment. **2. Analysis of Incorrect Options:** * **Option B (1, 2, 3 months):** Too frequent; does not cover the end-of-treatment assessment. * **Option C (3, 5, 6 months):** Misses the critical end-of-IP milestone (2 months) used to evaluate early treatment response. * **Option D (1, 3, 5 months):** Does not align with the standard 2-month IP and 6-month completion milestones. **High-Yield Clinical Pearls for NEET-PG:** * **Definition of Cure:** A patient who was initially smear-positive, completed treatment, and had negative smears on at least two occasions, one of which must be at the end of treatment (6th month). * **NTEP Update:** While RNTCP focused on microscopy, the current **NTEP** prioritizes **NAAT (CBNAAT/Truenat)** for diagnosis, but follow-up monitoring still relies on sputum microscopy. * **Category II:** Previously, for retreatment cases, the schedule was 3, 5, and 8 months. However, Category II has been phased out under recent "Daily Regimen" guidelines.

Q: What is the clinical incubation period of Filariasis?

8 to 16 months. ### Explanation The **clinical incubation period** of Filariasis (specifically Lymphatic Filariasis caused by *Wuchereria bancrofti*) refers to the time interval between the entry of infective larvae ($L_3$) via a mosquito bite and the manifestation of clinical symptoms. **1. Why Option C is Correct:** In Filariasis, the clinical incubation period is typically **8 to 16 months**. This prolonged duration is due to the slow maturation of the larvae into adult worms within the lymphatic system. Clinical symptoms, such as lymphangitis and retrograde fever, only appear once the adult worms begin to cause inflammatory and obstructive changes in the lymphatics. **2. Analysis of Incorrect Options:** * **Option A (10 to 20 days):** This is far too short for Filariasis. This timeframe is more characteristic of the **Pre-patent period** (the time between infection and the appearance of microfilariae in the blood), which is actually about 6–12 months, or the extrinsic incubation period in the mosquito (10–14 days). * **Option B & D (3 to 6 months / 6 to 12 months):** While these represent the time required for larvae to reach the adult stage, they generally precede the onset of overt clinical disease. Clinical symptoms usually lag behind the biological maturation of the parasite. **3. NEET-PG High-Yield Pearls:** * **Extrinsic Incubation Period:** 10 to 14 days (occurs within the *Culex* mosquito). * **Pre-patent Period:** 6 to 12 months (time until microfilariae are detectable in peripheral blood). * **Biological Vector:** *Culex quinquefasciatus* is the most common vector in India. * **Drug of Choice:** Diethylcarbamazine (DEC) 6 mg/kg for 12 days. * **Mass Drug Administration (MDA):** Annual single dose of DEC + Albendazole (or Ivermectin in specific areas).

Q: Transmission of hepatitis A virus occurs when?

Two weeks before onset of symptoms. **Explanation:** The transmission of Hepatitis A Virus (HAV) primarily occurs via the **fecal-oral route**. The period of maximum infectivity is during the late incubation period and the prodromal phase, specifically **two weeks before the onset of clinical jaundice (symptoms)**. **1. Why Option B is correct:** During the two weeks preceding the onset of symptoms, the concentration of HAV in the stool is at its peak (secondary to viral replication in the liver and subsequent excretion in bile). This is the "window of high infectivity" because the patient is asymptomatic but shedding massive amounts of the virus, leading to easy transmission in the community. **2. Why other options are incorrect:** * **Option A & C:** While viral shedding can persist for a short time after symptoms appear, the concentration of the virus in the stool drops significantly once jaundice develops. By the end of the first week of jaundice, the patient is generally considered non-infectious. Therefore, "two weeks after" is clinically inaccurate for the peak transmission period. * **Option D:** Since the infectivity is heavily front-loaded (pre-icteric phase), "All of the above" is incorrect. **High-Yield NEET-PG Pearls:** * **Incubation Period:** 15–45 days (Average: 28 days). * **Secondary Attack Rate (SAR):** High among household contacts. * **Diagnosis:** IgM anti-HAV is the gold standard for acute infection. IgG anti-HAV indicates past infection or immunity. * **Control:** The most effective preventive measure is the Hepatitis A vaccine and improving environmental sanitation (handwashing and safe water). * **Note:** Hepatitis A does **not** lead to chronic carrier states or cirrhosis, unlike Hepatitis B or C.

Q: What is the true infectivity period of hepatitis A?

2-3 weeks before and 1 week after the onset of jaundice. **Explanation:** The infectivity of Hepatitis A Virus (HAV) is closely linked to the concentration of the virus excreted in the feces. The maximum viral shedding occurs during the late incubation period and the prodromal (pre-icteric) phase. **1. Why Option D is Correct:** According to standard epidemiological data (Park’s PSM), the period of maximum infectivity for Hepatitis A begins **2 to 3 weeks before** the onset of jaundice and continues for about **1 week after** the appearance of jaundice. By the time jaundice is clinically apparent, the viral titer in the stool begins to decline rapidly, and most patients are non-infectious by the end of the first week of the icteric phase. **2. Analysis of Incorrect Options:** * **Options A & C:** These suggest a 2-week post-jaundice infectivity period. While viral RNA can sometimes be detected longer, the "true infectivity" (the period where transmission is epidemiologically significant) typically ceases after 7 days of jaundice. * **Option B:** This underestimates the pre-icteric infectivity. The virus starts shedding significantly as early as 2-3 weeks before symptoms appear, making this the most dangerous period for community transmission. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mode of Transmission:** Primarily feco-oral; common in areas with poor sanitation. * **Secondary Attack Rate (SAR):** High among household contacts (approx. 20%). * **Diagnosis:** IgM anti-HAV is the gold standard for acute infection. * **Vaccination:** Live attenuated (H2 strain) or Inactivated vaccines are available. * **Post-exposure Prophylaxis:** Best given within 2 weeks of exposure (Vaccine or Immunoglobulin). * **Key Fact:** Hepatitis A does **not** cause chronic infection or a carrier state.

Question 1

The definition of extensively drug-resistant TB includes resistance to all of the following drugs, EXCEPT:

Accepted Answer

Ethambutol

Answer

Rifampicin

Answer

Isoniazide

Answer

Amikacin

Question 2

A 45-year-old, healthy nonsmoking woman with a normal BMI (24) has been found on two occasions to have a blood pressure of 145/95. She has no family history of premature coronary artery disease. For this patient, what is the most important next step to take to reduce morbidity and mortality from common medical conditions such as diabetes and cardiovascular disease?

Accepted Answer

Recommend an exercise program such as brisk walking for at least 30 minutes per day and a low salt, Dietary Approaches to Stop Hypertension (DASH) diet.

Answer

Urge the patient to quit smoking and discuss the various available medications to assist in the process.

Answer

Prescribe a low-cholesterol diet and statin drug.

Answer

Recommend aspirin (81 mg) daily.

Question 3

Which of the following is NOT true of Kyasanur Forest Disease?

Accepted Answer

Caused by a retrovirus

Answer

Transmitted by soft ticks

Answer

Incubation period is 3-8 days

Answer

A killed vaccine is available

Question 4

What is the time gap between the appearance of Koplik's spots and the cutaneous rash in measles?

Accepted Answer

3-4 days

Answer

24 hours

Answer

2 weeks

Answer

10 days

Question 5

In RNTCP, what is the schedule for sputum examination after beginning chemotherapy in Category I patients?

Accepted Answer

2, 4, and 6 months

Answer

1, 2, and 3 months

Answer

3, 5, and 6 months

Answer

1, 3, and 5 months

Question 6

What is the clinical incubation period of Filariasis?

Accepted Answer

8 to 16 months

Answer

10 to 20 days

Answer

3 to 6 months

Answer

6 to 12 months

Question 7

Management of non-immunized diphtheria contacts includes all of the following except:

Accepted Answer

Prophylactic penicillin, daily throat examinations, and throat swab culture

Answer

Prophylactic penicillin and throat swab culture

Answer

Prophylactic penicillin and daily throat examinations

Answer

Single dose of toxoid and throat swab culture

Question 8

Transmission of hepatitis A virus occurs when?

Accepted Answer

Two weeks before onset of symptoms

Answer

One week before and one week after onset of symptoms

Answer

Two weeks after onset of symptoms

Answer

All of the above

Question 9

What is the true infectivity period of hepatitis A?

Accepted Answer

2-3 weeks before and 1 week after the onset of jaundice

Answer

1-2 weeks before and 2 weeks after the onset of jaundice

Answer

1-2 weeks before and 1 week after the onset of jaundice

Answer

2-3 weeks before and 2 weeks after the onset of jaundice

Question 10

Which of the following statements is true regarding meningococcal meningitis?

Accepted Answer

Treatment within the first 2 days can save the lives of 95% of cases.

Answer

The case fatality rate is less than 10% in untreated cases.

Answer

Asymptomatic carriers are the main source of infection.

Answer

Rifampicin is the drug of choice for treatment.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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