Infectious Diseases Practice Questions

Q: Which drugs can be used for outpatient treatment of community-acquired pneumonia?

Azithromycin. **Explanation:** **Correct Answer: D. Azithromycin** Community-acquired pneumonia (CAP) in the outpatient setting is most commonly caused by *Streptococcus pneumoniae*, *Haemophilus influenzae*, and atypical pathogens like *Mycoplasma pneumoniae* or *Chlamydophila pneumoniae*. **Azithromycin**, a macrolide, is a preferred first-line agent for healthy outpatients because it provides excellent coverage against both typical and atypical pathogens. It is orally bioavailable, has a long half-life (allowing for once-daily dosing), and achieves high intracellular concentrations in lung tissue. **Analysis of Incorrect Options:** * **A. Ceftriaxone:** While effective against *S. pneumoniae*, it is a parenteral (IV/IM) third-generation cephalosporin. It is typically reserved for inpatient management or as part of a combination regimen for more severe cases. * **B. Cefazolin:** A first-generation cephalosporin with excellent Gram-positive coverage (especially *S. aureus*) but poor activity against the common respiratory pathogens and no activity against atypical organisms. * **C. Imipenem:** A carbapenem used for serious, multi-drug resistant, or hospital-acquired infections. It must be administered parenterally and is "overkill" for uncomplicated outpatient CAP. **High-Yield Clinical Pearls for NEET-PG:** * **ATS/IDSA Guidelines:** For healthy outpatients with no comorbidities, the preferred drugs are **Amoxicillin (high dose)**, **Doxycycline**, or a **Macrolide** (if local pneumococcal resistance is <25%). * **Atypical Coverage:** Macrolides (Azithromycin) and Tetracyclines (Doxycycline) are the drugs of choice for "Walking Pneumonia" (Mycoplasma). * **Side Effect:** Watch for **QT interval prolongation** with macrolides and fluoroquinolones. * **Ceftriaxone + Azithromycin:** This is the classic "dual therapy" for hospitalized patients to cover both typical and atypical pathogens.

Q: A 62-year-old man presents with new symptoms of fevers, chills, and malaise. His past medical history is significant for a prosthetic aortic valve replacement 5 years ago due to aortic stenosis from a bicuspid valve. On physical examination, the blood pressure is 130/85 mm Hg, heart rate is 88/min, and temperature is 38.5°C. He has a 2/6 systolic ejection murmur heard best at the aortic region and a mechanical second heart sound, but no other abnormalities on examination. Blood cultures are most likely to grow which of the following organisms?

Staphylococcus epidermidis. The patient presents with symptoms of **Prosthetic Valve Endocarditis (PVE)**. The key to identifying the causative organism in PVE is the **timing** of symptom onset after surgery. 1. **Why D is correct:** PVE is classified into early ( 1 year) onset [1]. While **Staphylococcus epidermidis** (Coagulase-negative Staphylococci) is the most common cause of *early* PVE due to perioperative contamination, it remains a significant pathogen in late PVE as well. However, in the context of NEET-PG questions, if a patient has a prosthetic valve and the clinical picture suggests endocarditis, **Staphylococci** (specifically *S. epidermidis*) are the most frequently implicated organisms across various stages of the disease due to their ability to form biofilms on prosthetic material [1]. 2. **Why other options are incorrect:** * **A & B (Fungi/Bartonella):** These are causes of "Culture-Negative Endocarditis." While they occur, they are far less common than bacterial causes. * **C (Diphtheroids):** *Corynebacterium* species are rare causes of PVE and are usually considered contaminants unless isolated from multiple blood cultures. **Clinical Pearls for NEET-PG:** * **Early PVE ( 12 months):** The microbiology starts to resemble Native Valve Endocarditis (NVE) [4], with *Streptococcus* species and *Staphylococcus aureus* becoming more prevalent. However, *S. epidermidis* remains a high-yield answer for any prosthetic material infection. * **Duke’s Criteria:** Remember that a new valvular regurgitation or positive blood cultures are "Major Criteria" for diagnosis [2]. * **Treatment:** PVE caused by *S. epidermidis* usually requires a combination of Vancomycin + Rifampin + Gentamicin [3].

Q: Dengue haemorrhagic fever (DHF) is suspected if all of the following are present EXCEPT?

Evidence of lymphadenopathy. **Explanation:** The diagnosis of **Dengue Haemorrhagic Fever (DHF)** is based on a specific constellation of clinical and laboratory findings defined by the WHO. The hallmark that distinguishes DHF from Dengue Fever (DF) is **plasma leakage**. **Why "Evidence of lymphadenopathy" is the correct answer:** While lymphadenopathy can occur in classical Dengue Fever (DF), it is **not** a diagnostic criterion for DHF. The WHO criteria for DHF require the presence of all four of the following: 1. **Fever:** Acute onset, high grade, and usually lasting **2 to 7 days**. 2. **Hemorrhagic manifestations:** Positive tourniquet test, petechiae, or mucosal bleeding. 3. **Thrombocytopenia:** Platelet count ** 20% rise in hematocrit, pleural effusion, or ascites). **Analysis of other options:** * **Option A (Fever duration):** While DHF fever typically lasts 2–7 days, the question asks for what is *not* a criterion. However, a fever lasting **over 10 days** is highly atypical for Dengue and usually suggests an alternative diagnosis (like Typhoid or Malaria). In the context of this specific MCQ, lymphadenopathy is the most "unrelated" clinical sign to the DHF diagnostic triad. * **Option B (Evidence of bleeding):** This is a core requirement for DHF (the "Hemorrhagic" component). * **Option C (Thrombocyte count < 100,000):** This is a mandatory laboratory criterion for DHF. **High-Yield Clinical Pearls for NEET-PG:** * **Critical Phase:** Occurs during defervescence (day 3–7). This is when plasma leakage and **Dengue Shock Syndrome (DSS)** typically develop. * **Best Indicator of Plasma Leakage:** Hemoconcentration (rising Hematocrit). * **Tourniquet Test:** Positive if ≥10–20 petechiae per square inch. * **Grading:** DHF is divided into 4 grades; Grades III and IV are classified as DSS.

Q: Which of the following types of hepatitis is associated with an immune-mediated vasculitis characterized by p-ANCA antibodies?

Hepatitis B. **Explanation:** The correct answer is **Hepatitis B**. This association is a classic high-yield concept in medical pathology and clinical medicine. **1. Why Hepatitis B is correct:** Hepatitis B virus (HBV) is strongly associated with **Polyarteritis Nodosa (PAN)**, a systemic necrotizing vasculitis of medium and small-sized arteries. PAN is an immune-complex mediated disease where HBsAg-anti-HBs complexes deposit in vessel walls, leading to inflammation [1]. While PAN is classically "pauci-immune" (meaning ANCA is usually negative), a specific subset of patients—particularly those with microscopic polyangiitis or certain variants of PAN—can demonstrate **p-ANCA (perinuclear Anti-Neutrophil Cytoplasmic Antibodies)** positivity. Approximately 10–30% of patients with PAN are chronic carriers of HBV. **2. Why other options are incorrect:** * **Hepatitis A:** This is an acute, self-limiting infection transmitted via the fecal-oral route [2]. It is not associated with chronic immune-complex mediated vasculitides. * **Hepatitis C:** HCV is most famously associated with **Mixed Cryoglobulinemia** (Type II and III), which presents with the triad of purpura, arthralgia, and weakness. While it causes vasculitis, it is not typically associated with p-ANCA. * **Hepatitis D:** HDV requires the presence of HBV to replicate. While it increases the severity of liver disease, the specific association with p-ANCA vasculitis is primarily attributed to the underlying HBV infection. **Clinical Pearls for NEET-PG:** * **PAN Presentation:** Look for "string of beads" appearance on angiography, hypertension (renal artery involvement), and mononeuritis multiplex. * **HCV vs. HBV:** If the question mentions **Cryoglobulins**, think **HCV**. If it mentions **PAN or p-ANCA**, think **HBV** [1]. * **Rule of Thumb:** PAN characteristically **spares the lungs**, unlike other ANCA-associated vasculitides like Granulomatosis with Polyangiitis (GPA).

Q: Mild steatorrhea is caused by which of the following?

Giardia. **Explanation:** **Giardia lamblia** is the correct answer because it primarily infects the upper small intestine (duodenum and jejunum) [2]. The pathophysiology involves the trophozoites adhering to the intestinal mucosa via a ventral sucking disc [2]. This leads to the **blunting of villi** and the **malabsorption of fats**, resulting in characteristic foul-smelling, greasy, non-bloody stools known as **steatorrhea**. Unlike invasive pathogens, *Giardia* causes a functional deficiency of enzymes (like disaccharidases) and interferes with bile salt activity, further contributing to fat malabsorption. **Analysis of Incorrect Options:** * **Trichomonas vaginalis:** This is a flagellated protozoan that causes urogenital infections (vaginitis/urethritis), not intestinal disease. It is a common cause of "strawberry cervix." * **Entamoeba histolytica:** This organism causes amoebic dysentery [1]. It invades the colonic mucosa, leading to "flask-shaped ulcers" and bloody diarrhea (hematochezia), rather than malabsorptive steatorrhea [1]. * **Entamoeba coli:** This is considered a non-pathogenic commensal of the human colon. Its presence in stool indicates fecal-oral contamination but does not cause clinical disease or steatorrhea. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Tinidazole (single dose) or Metronidazole. * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **String Test (Entero-test)** if stool samples are negative. * **Risk Factors:** Common in travelers ("Traveler’s Diarrhea"), hikers (drinking unfiltered stream water), and individuals with **IgA deficiency** [2][3]. * **Morphology:** Trophozoites have a characteristic "falling leaf" motility and a "monkey face" appearance on staining.

Question 1

Which drugs can be used for outpatient treatment of community-acquired pneumonia?

Accepted Answer

Azithromycin

Answer

Ceftriaxone

Answer

Cefazolin

Answer

Imipenem

Question 2

A 22-year-old man with AIDS complains of persistent cough, night sweats, low-grade fever, and general malaise. A chest X-ray reveals an area of consolidation in the periphery of the left upper lobe, as well as hilar lymphadenopathy. Sputum cultures show acid-fast bacilli. Which of the following is the most likely diagnosis?

Accepted Answer

Tuberculosis

Answer

Bronchopneumonia

Answer

Pulmonary abscess

Answer

Sarcoidosis

Question 3

A 49-year-old gentleman undergoes a root canal procedure. A few days later, he develops fever, weight loss, and anorexia. He is diagnosed with mitral valve prolapse with mitral regurgitation. What is the most common organism implicated in the causation of this condition?

Accepted Answer

Viridans streptococci

Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Providencia stuartii

Question 4

A 62-year-old man presents with new symptoms of fevers, chills, and malaise. His past medical history is significant for a prosthetic aortic valve replacement 5 years ago due to aortic stenosis from a bicuspid valve. On physical examination, the blood pressure is 130/85 mm Hg, heart rate is 88/min, and temperature is 38.5°C. He has a 2/6 systolic ejection murmur heard best at the aortic region and a mechanical second heart sound, but no other abnormalities on examination. Blood cultures are most likely to grow which of the following organisms?

Accepted Answer

Staphylococcus epidermidis

Answer

Fungi

Answer

Bartonella

Answer

Diphtheroids

Question 5

A 70-year-old male presented with complaints of abdominal pain, nausea, headache, malaise, persistent fever for 2 weeks, and constipation. On examination, a characteristic rash was observed on the trunk and chest. His vital signs were BP 120/70 mm Hg and HR 65 bpm. Examination revealed hepatomegaly and splenomegaly. Blood culture was negative; however, a bone marrow culture showed a Gram-negative organism that ferments glucose with acid production, reduces nitrates, does not ferment lactose, and is motile by means of flagella. What is the drug of choice if the isolated organism is a multi-drug resistant variety?

Accepted Answer

Ceftriaxone

Answer

Ciprofloxacin

Answer

Moxifloxacin

Answer

Ceftazidime

Question 6

Dengue haemorrhagic fever (DHF) is suspected if all of the following are present EXCEPT?

Accepted Answer

Evidence of lymphadenopathy

Answer

Fever of over 10 days duration

Answer

Evidence of bleeding

Answer

Thrombocyte count less than 100,000/cmm

Question 7

A patient presents with lower gastrointestinal bleed. Sigmoidoscopy shows ulcers in the sigmoid. Biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

Accepted Answer

Intravenous metronidazole

Answer

Intravenous ceftriaxone

Answer

Intravenous steroids and sulphasalazine

Answer

Hydrocortisone enemas

Question 8

Which of the following types of hepatitis is associated with an immune-mediated vasculitis characterized by p-ANCA antibodies?

Accepted Answer

Hepatitis B

Answer

Hepatitis A

Answer

Hepatitis C

Answer

Hepatitis D

Question 9

A patient who underwent renal transplantation 2 months ago presents with difficulty breathing. Chest X-ray shows bilateral diffuse interstitial pneumonia. What is the probable etiologic agent?

Accepted Answer

Cytomegalovirus (CMV)

Answer

Histoplasma capsulatum

Answer

Candida species

Answer

Pneumocystis jirovecii

Question 10

Mild steatorrhea is caused by which of the following?

Accepted Answer

Giardia

Answer

Trichomonas vaginalis

Answer

E. histolytica

Answer

Entamoeba coli

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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