Infectious Diseases Practice Questions

Q: Waterhouse-Friderichsen syndrome is caused by which organism?

Neisseria meningitidis. **Explanation:** **Waterhouse-Friderichsen Syndrome (WFS)** is a catastrophic complication of severe sepsis characterized by **bilateral adrenal hemorrhage**, leading to acute primary adrenal insufficiency. **Why Neisseria meningitidis is correct:** While various pathogens can cause WFS, **Neisseria meningitidis** (Meningococcus) is the most common causative organism. The pathogenesis involves severe meningococcemia leading to **Disseminated Intravascular Coagulation (DIC)**. This triggers widespread petechiae, purpura fulminans, and hemorrhagic necrosis of the adrenal glands. The resulting adrenal crisis causes profound hypotension and refractory shock. **Why the other options are incorrect:** * **Neisseria gonorrhoeae:** Primarily causes localized urogenital infections, pelvic inflammatory disease, or disseminated gonococcal infection (arthritis-dermatitis syndrome), but not adrenal hemorrhage. * **Chlamydia trachomatis:** An obligate intracellular bacterium causing trachoma and urogenital infections; it does not cause fulminant sepsis or WFS. * **Lymphogranuloma venereum (LGV):** This is a clinical condition caused by specific serovars (L1, L2, L3) of *C. trachomatis*, characterized by lymphadenopathy and proctitis, unrelated to adrenal failure. **Clinical Pearls for NEET-PG:** * **Triad of WFS:** Shock, widespread purpura, and acute adrenal insufficiency. * **Diagnosis:** Primarily clinical; CT scan may show bilateral adrenal enlargement/hemorrhage. * **Treatment:** Immediate IV antibiotics (Ceftriaxone) and **stress-dose glucocorticoids** (Hydrocortisone) to manage the adrenal crisis. * **Other causes:** Though rare, *S. pneumoniae*, *H. influenzae*, and *Staphylococcus aureus* can also cause WFS.

Q: Which of the following is NOT a characteristic feature of Kala-azar?

Leukocytosis. **Explanation:** Kala-azar (Visceral Leishmaniasis), caused by *Leishmania donovani*, is characterized by the parasite's invasion of the Reticuloendothelial System (RES), primarily affecting the spleen, liver, and bone marrow [1]. **Why Leukocytosis is the correct answer:** In Kala-azar, the hallmark hematological finding is **Pancytopenia** (reduction in all three blood cell lines). Instead of leukocytosis, patients typically present with **Leukopenia** (specifically neutropenia). This occurs due to bone marrow suppression and hypersplenism. Therefore, leukocytosis is NOT a feature of the disease. **Analysis of incorrect options:** * **Splenomegaly:** This is the most characteristic clinical sign [1]. The spleen undergoes massive enlargement (often crossing the midline) due to the proliferation of infected macrophages. * **Anemia:** This is a consistent feature resulting from bone marrow infiltration by amastigotes, splenic sequestration, and chronic inflammation. * **Hypoalbuminemia:** Chronic infection leads to a reversal of the Albumin-Globulin (A:G) ratio. While there is **Hypergammaglobulinemia** (polyclonal), albumin levels drop due to decreased hepatic synthesis and chronic illness. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Female Phlebotomus argentipes (Sandfly) [1]. * **Gold Standard Diagnosis:** Splenic aspirate (highest sensitivity) showing **LD bodies** (Amastigotes) [1]. * **Serology:** rK39 immunochromatographic test is the rapid test of choice [1]. * **Drug of Choice:** Liposomal Amphotericin B (single dose 10mg/kg is the current WHO recommendation for India). * **PKDL:** Post-Kala-azar Dermal Leishmaniasis occurs in 5-10% of cases after "apparent" cure, acting as a reservoir for the parasite.

Q: A 35-year-old woman presents with a 2-day history of burning on urination. Urinalysis shows marked positivity for leukocyte esterase but no reactivity for nitrite. Urine culture grows a large number of organisms. Which of the following bacteria is most likely responsible for this patient's infection?

Enterococcus faecalis. ### Explanation The key to solving this question lies in understanding the **Nitrite Test** on a urine dipstick. [1] **1. Why Enterococcus faecalis is correct:** The nitrite test depends on the ability of certain bacteria to reduce dietary nitrates into nitrites using the enzyme **nitrate reductase**. Most Gram-negative bacteria (Enterobacteriaceae) possess this enzyme. However, **Gram-positive organisms** like *Enterococcus faecalis* and *Staphylococcus saprophyticus* (and some Gram-negatives like *Acinetobacter* or *Pseudomonas*) lack nitrate reductase. Therefore, in a patient with symptomatic UTI and significant bacteriuria, a **negative nitrite test** strongly suggests a Gram-positive organism like *Enterococcus*. **2. Why the other options are incorrect:** * **Escherichia coli (Option C):** This is the most common cause of UTI. It is a member of the Enterobacteriaceae family and is a potent producer of nitrate reductase, typically resulting in a **positive** nitrite test. * **Klebsiella pneumoniae (Option D) and Enterobacter sp (Option A):** Both are Gram-negative bacilli belonging to the Enterobacteriaceae family. Like *E. coli*, they produce nitrate reductase and would typically result in a positive nitrite test. **3. NEET-PG High-Yield Pearls:** * **Leukocyte Esterase (LE):** Indicates the presence of pyuria (neutrophils). It is highly sensitive for UTI [1] but not specific for the causative organism. * **Nitrite Test False Negatives:** Can occur due to: 1. Organisms lacking nitrate reductase (*Enterococcus*, *S. saprophyticus*, *Pseudomonas*). 2. Insufficient time for conversion (urine must stay in the bladder for >4 hours). 3. Low dietary nitrate intake or highly acidic urine (pH < 6.0). * **Enterococcus** is a common cause of healthcare-associated UTIs and is inherently resistant to cephalosporins.

Q: What is the most likely diagnosis in this patient with cough?

Sarcoidosis. ***Sarcoidosis*** - **Bilateral hilar lymphadenopathy** on chest X-ray is a classic finding in sarcoidosis, especially in young adults with respiratory symptoms. - Presents with **dry cough**, dyspnea, and systemic symptoms; often has **non-caseating granulomas** on biopsy. *Aspergillosis* - Typically causes **cavitary lesions** or **aspergilloma** formation on chest imaging, not bilateral hilar lymphadenopathy. - More common in **immunocompromised patients** or those with pre-existing lung disease like asthma or COPD. *Coccidioidomycosis* - Endemic to **southwestern United States** and presents with **unilateral hilar adenopathy** or pulmonary nodules. - Often associated with **travel history** to endemic areas and may cause **erythema nodosum** as extrapulmonary manifestation. *Granuloma annulare* - A **dermatologic condition** characterized by ring-shaped skin lesions, not a pulmonary disease. - Does not cause respiratory symptoms or **chest X-ray abnormalities**.

Q: The definition of FUO (fever of unknown origin) requires fever lasting for more than how many weeks?

3 weeks. ### Explanation The classic definition of **Fever of Unknown Origin (FUO)** was established by Petersdorf and Beeson in 1961. To meet the criteria for FUO, a patient must satisfy three specific requirements: 1. **Temperature:** Fever > 38.3°C (101°F) on several occasions (modern definitions often use a threshold of 38.0°C) [1]. 2. **Duration:** Fever lasting for **more than 3 weeks** [1]. 3. **Uncertain Diagnosis:** Failure to reach a diagnosis after 1 week of inpatient investigation (modern definitions now include 3 days of hospital investigation or 3 outpatient visits) [1]. **Why 3 weeks?** The 3-week threshold is designed to exclude self-limiting viral illnesses (which typically resolve within 7–14 days) and allow sufficient time for standard diagnostic workups to be completed. #### Analysis of Options: * **A (1 week):** This is too short; most acute febrile illnesses (like the common cold or influenza) last about a week and do not require the extensive workup associated with FUO. * **B (2 weeks):** While many infections persist into the second week, the 3-week mark is the standardized academic and clinical cutoff to differentiate "prolonged fever" from true FUO. * **D (4 weeks):** While a fever lasting 4 weeks certainly qualifies as FUO, the *minimum* requirement defined in medical literature is 3 weeks. #### NEET-PG High-Yield Pearls: * **Most Common Cause:** In developing countries like India, **Infections** (specifically Tuberculosis) remain the leading cause of FUO. In developed nations, non-infectious inflammatory diseases (connective tissue disorders) and malignancies are equally prevalent. * **Categories of FUO:** Modern medicine classifies FUO into four types: **Classic, Nosocomial, Neutropenic, and HIV-associated.** [1] * **Factitious Fever:** Always consider this in patients (often healthcare workers) with prolonged fever, no tachycardia during spikes, and rapid defervescence without sweating [2].

Question 1

Waterhouse-Friderichsen syndrome is caused by which organism?

Accepted Answer

Neisseria meningitidis

Answer

Neisseria gonorrhoeae

Answer

Chlamydia trachomatis

Answer

Lymphogranuloma venereum

Question 2

A 19-year-old male presents with a 1-week history of malaise and anorexia followed by fever and sore throat. On physical examination, the throat is inflamed without exudate, and there are a few palatal petechiae. Cervical adenopathy is present. The liver is percussed at 12 cm and the spleen is palpable. Throat cultures are negative for group A streptococci, and peripheral blood smears show atypical lymphocytosis. Laboratory findings include: Hb: 12 g/dL, Reticulocytes: 4%, WBC: 14,000/uL with 60% Lymphocytes, Total Bilirubin: 2.0 mg/dL, LDH: 260 IU/L, AST: 40 U/L, and ALT: 35 U/L. What is the next best investigation?

Accepted Answer

Heterophile antibody test

Answer

Hepatitis B IgM antibody

Answer

Cytomegalovirus IgG antibody

Answer

ASLO titer

Question 3

Which of the following is NOT a characteristic feature of Kala-azar?

Accepted Answer

Leukocytosis

Answer

Splenomegaly

Answer

Anemia

Answer

Hypoalbuminemia

Question 4

Occurrence of diplopia, dysphagia, dysarthria, blurring of vision, and muscle weakness could be due to which of the following?

Accepted Answer

Botulism

Answer

Diphtheria

Answer

Infantile beriberi

Answer

Myasthenia gravis

Question 5

A 35-year-old woman presents with a 2-day history of burning on urination. Urinalysis shows marked positivity for leukocyte esterase but no reactivity for nitrite. Urine culture grows a large number of organisms. Which of the following bacteria is most likely responsible for this patient's infection?

Accepted Answer

Enterococcus faecalis

Answer

Enterobacter sp

Answer

Escherichia coli

Answer

Klebsiella pneumoniae

Question 6

Pulmonary tuberculosis is more common in the following associated diseases, except:

Accepted Answer

Mitral stenosis

Answer

Acquired Immunodeficiency Syndrome (AIDS)

Answer

Diabetes Mellitus

Answer

Chronic renal failure

Question 7

A 20-year-old woman presents with a 2-week history of fever, malaise, and brown-colored urine. She recently visited Mexico. Physical examination reveals jaundice, mild hepatomegaly, and tenderness in the right upper quadrant. The serum bilirubin is 7.8 mg/dL, with 60% in the conjugated form. Serum levels of AST and ALT are markedly elevated (400 and 392 U/L, respectively). Serum albumin and immunoglobulin levels are normal. Serum IgM anti-hepatitis A virus (anti-HAV) is positive. IgG anti-hepatitis B surface antigen (anti-HBsAg) antibodies are positive. Anti-hepatitis C virus antibodies are negative. What is the most likely diagnosis?

Accepted Answer

Acute viral hepatitis A

Answer

Acute viral hepatitis B

Answer

Acute viral hepatitis C

Answer

Autoimmune hepatitis

Question 8

What is the most likely diagnosis in this patient with cough?

Accepted Answer

Sarcoidosis

Answer

Aspergillosis

Answer

Coccidioidomycosis

Answer

Granuloma annulare

Question 9

What is the treatment of choice for a patient with meningococcal meningitis who is allergic to penicillin?

Accepted Answer

Chloramphenicol

Answer

Meropenem

Answer

Linezolid

Answer

Teicoplanin

Question 10

The definition of FUO (fever of unknown origin) requires fever lasting for more than how many weeks?

Accepted Answer

3 weeks

Answer

1 week

Answer

2 weeks

Answer

4 weeks

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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