Infectious Diseases Practice Questions

Q: 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?

Intravenous metronidazole. **Explanation:** The clinical presentation of lower gastrointestinal bleeding combined with the pathognomonic finding of **flask-shaped ulcers** on biopsy is diagnostic of **Amoebic Colitis**, caused by *Entamoeba histolytica*. [1] 1. **Why Intravenous Metronidazole is correct:** *Entamoeba histolytica* trophozoites secrete proteolytic enzymes (histolysins) that breach the colonic mucosa. Once they reach the submucosa, they spread laterally, creating the characteristic narrow-necked, wide-based "flask-shaped" ulcer. **Metronidazole** (or Tinidazole) is the drug of choice as it is a potent tissue amoebicide that kills the invasive trophozoites. In cases of active GI bleed or severe colitis, the intravenous route is preferred to ensure rapid therapeutic levels. 2. **Why other options are incorrect:** * **Option A:** Ceftriaxone is a third-generation cephalosporin used for bacterial infections (like enteric fever or peritonitis) but has no activity against protozoa like *E. histolytica*. * **Options C & D:** Steroids and Sulphasalazine are used to treat Inflammatory Bowel Disease (IBD), specifically Ulcerative Colitis [2]. Administering steroids in a patient with amoebic colitis is dangerous and contraindicated, as it can lead to toxic megacolon or perforation. **High-Yield Clinical Pearls for NEET-PG:** * **Site:** The most common site for amoebic ulcers is the **Cecum** and ascending colon, but they can involve the sigmoid. * **Microscopy:** Look for trophozoites with **ingested RBCs** (erythrophagocytosis) in the stool or biopsy. * **Treatment Protocol:** Always follow a tissue amoebicide (Metronidazole) with a **luminal amoebicide** (e.g., Paromomycin or Diloxanide furoate) to eradicate the cyst stage and prevent relapse/transmission. * **Complication:** The most common extra-intestinal site is the liver (**Amoebic Liver Abscess**), typically presenting with "anchovy sauce" pus [1].

Q: What is the most common extrahepatic complication of amoebic hepatitis?

Lung abscess. **Explanation:** Amoebic liver abscess (ALA), caused by *Entamoeba histolytica*, is the most common extra-intestinal manifestation of amoebiasis. When complications occur, they usually result from the direct extension or rupture of the abscess into adjacent structures. **1. Why Lung Abscess is Correct:** The liver is situated immediately below the diaphragm. The most common route of spread for an amoebic liver abscess is **direct extension through the diaphragm** into the thoracic cavity. This leads to pleuropulmonary amoebiasis, manifesting most frequently as a **lung abscess** (typically in the lower lobe of the right lung) or an empyema. Patients often present with a "chocolate-sauce" or "anchovy-paste" sputum if a hepatobronchial fistula forms. **2. Why Other Options are Incorrect:** * **Meningitis & Encephalitis:** While *E. histolytica* can spread hematogenously to the brain causing cerebral amoebiasis, this is extremely rare (less than 1% of cases) and usually occurs as a terminal event. (Note: Primary Amoebic Meningoencephalitis is caused by *Naegleria fowleri*, not *E. histolytica*). * **Nephritis:** Renal involvement in amoebiasis is exceptionally rare and is not a recognized standard complication of amoebic hepatitis. **Clinical Pearls for NEET-PG:** * **Most common site of ALA:** Right lobe of the liver (due to the bulk of tissue and portal blood flow distribution). * **Characteristic Pus:** Described as **"Anchovy sauce" appearance** (consists of liquefied hepatocytes and blood, but notably lacks host inflammatory cells/neutrophils). * **Diagnosis:** Serology (ELISA) is highly sensitive; Ultrasound is the initial imaging of choice. * **Treatment:** Drug of choice is **Metronidazole** followed by a luminal amoebicide (e.g., Diloxanide furoate) to eradicate the intestinal cyst stage.

Q: A resident doctor sustained a needlestick injury while sampling blood of a patient who is HIV positive. A decision is taken to offer him post-exposure prophylaxis. Which one of the following would be the best recommendation?

Zidovudine + Lamivudine + Indinavir for 4 weeks. The management of occupational exposure to HIV (Post-Exposure Prophylaxis - PEP) is a high-yield topic for NEET-PG. The goal of PEP is to prevent viral replication immediately after exposure [1]. **1. Why Option C is Correct:** According to the classic guidelines (NACO/WHO) reflected in this question, PEP for a "high-risk" exposure (e.g., a hollow-bore needle stick from a known HIV-positive patient) requires an **Expanded Regimen**. This consists of **two NRTIs plus a Protease Inhibitor (PI)** [3]. * **Zidovudine + Lamivudine** (NRTIs) form the backbone. * **Indinavir** (or Lopinavir/Ritonavir) is added as the third drug to increase potency [3]. * The duration for all PEP regimens is strictly **4 weeks (28 days)**. **2. Why Other Options are Incorrect:** * **Option A:** This is a "Basic Regimen." While used for low-risk exposures (e.g., solid needle, superficial injury), it is not the "best" recommendation for a needle stick from a confirmed HIV-positive source. * **Option B & D:** These include **Nevirapine** (an NNRTI). Nevirapine is strictly **contraindicated** in PEP because it carries a high risk of severe hepatotoxicity and Stevens-Johnson Syndrome (SJS) in HIV-negative individuals. **Stavudine** (in Option D) is also avoided due to high toxicity. **3. Clinical Pearls for NEET-PG:** * **Timing:** PEP should ideally be started within **2 hours**, and definitely within **72 hours** of exposure. * **Current Update:** While this question reflects the classic PI-based exam pattern, current WHO/NACO guidelines now prefer **Tenofovir + Lamivudine + Dolutegravir (TLD)** as the single preferred regimen for all exposures. * **Testing Schedule:** Follow-up HIV testing for the healthcare worker should be done at baseline, 6 weeks, 12 weeks, and 6 months [1]. * **Risk of Transmission:** The average risk of HIV transmission after a percutaneous skin puncture is approximately **0.3%** [2].

Q: A 50-year-old HIV-positive male presents with fever and breathlessness, diagnosed with Pneumocystis jiroveci pneumonia (PCP). At what CD4 T cell count is primary prophylaxis for PCP recommended?

< 200 cells/mm³. Pneumocystis jiroveci pneumonia (PCP) is the most common opportunistic infection in patients with HIV/AIDS. The risk of developing PCP increases significantly as the immune system weakens, specifically when the CD4+ T-lymphocyte count falls below 200 cells/mm³ [1]. Therefore, primary prophylaxis is initiated at this threshold to prevent the first occurrence of the disease. * Option A (Correct): Guidelines (CDC/WHO) recommend starting prophylaxis with Trimethoprim-Sulfamethoxazole (TMP-SMX) when CD4 < 200 cells/mm³ or if the patient has a history of oropharyngeal candidiasis [1]. * Option B (< 50 cells/mm³): This is the threshold for prophylaxis against Mycobacterium avium complex (MAC) (using Azithromycin) and is associated with increased risk for CMV retinitis. * Option C (< 150 cells/mm³): This threshold is used in specific endemic areas for prophylaxis against Histoplasma capsulatum. * Option D (< 100 cells/mm³): This is the threshold for starting prophylaxis against Toxoplasma gondii (in IgG-positive patients) and Cryptococcus neoformans (pre-emptive screening/treatment). Clinical Pearls for NEET-PG: 1. Drug of Choice: TMP-SMX (Double strength, once daily) is the gold standard for both prophylaxis and treatment [1]. 2. Alternative: If the patient is allergic to Sulfa drugs, use Dapsone or Atovaquone [1]. 3. Steroid Indication: In active PCP treatment, add corticosteroids if PaO₂ 35 mmHg to prevent respiratory failure [1]. 4. Discontinuation: Prophylaxis can be safely stopped when CD4 counts rise above 200 cells/mm³ for at least 3 months in response to ART.

Q: Regarding chronic hepatitis B, all of the following are true EXCEPT:

Chronicity if infected in adulthood is about 10%.. The risk of developing chronic Hepatitis B (HBV) is inversely proportional to the age at which the infection is acquired. This is due to the maturity of the host’s immune system. **1. Why Option D is the Correct Answer (The False Statement):** In immunocompetent adults, the risk of chronicity following an acute HBV infection is actually **less than 5%** (typically 1–3%) [1]. A 10% figure is an overestimation for healthy adults. The adult immune system is usually robust enough to mount a vigorous T-cell response, leading to viral clearance in the vast majority of cases. **2. Analysis of Other Options:** * **Option A:** Perinatal transmission (at birth) carries the highest risk of chronicity, approximately **90%**, because the neonatal immune system is immature and develops "immune tolerance" to the virus [1]. * **Option B:** Patients with mild chronic hepatitis B (compensated) have an excellent prognosis, with a **5-year survival rate of approximately 97%**. Survival drops significantly once cirrhosis or hepatocellular carcinoma (HCC) develops. * **Option C:** Unlike childhood infections which are mostly asymptomatic, **adult-acquired HBV is usually symptomatic** (jaundice, malaise, nausea) in about 30–50% of cases, reflecting the active immune-mediated destruction of infected hepatocytes. **Clinical Pearls for NEET-PG:** * **Serology:** The hallmark of chronic HBV is the persistence of **HBsAg for >6 months** [1]. * **Transmission:** Globally, the most common route is perinatal [1]; in low-prevalence areas, it is sexual or percutaneous. * **Ground Glass Hepatocytes:** The characteristic histopathological finding in chronic HBV due to HBsAg accumulation in the endoplasmic reticulum. * **Extrahepatic Manifestation:** Polyarteritis Nodosa (PAN) and Membranous Glomerulonephritis are strongly associated with chronic HBV.

Q: What is the most common complication of Typhoid fever?

Paralytic ileus. **Explanation:** **Typhoid fever (Enteric fever)**, caused by *Salmonella Typhi*, primarily affects the gastrointestinal tract, specifically the Peyer's patches in the terminal ileum. **Why Paralytic Ileus is the correct answer:** During the third week of untreated typhoid fever, the inflammatory process in the Peyer's patches leads to necrosis and ulceration [1]. This intense inflammation and toxemia often result in **paralytic ileus** (adynamic ileus), which is considered the **most common gastrointestinal complication**. It presents with abdominal distension and absent bowel sounds [1]. If the ulceration progresses deeper, it can lead to more severe (but statistically less frequent) complications like intestinal perforation or hemorrhage [1]. **Analysis of Incorrect Options:** * **B. Otitis media:** While a common complication of respiratory infections (like Measles or Streptococcal infections), it is not a characteristic feature of Typhoid fever. * **C. Oophoritis:** This is a classic complication of **Mumps** in post-pubertal females, not Typhoid. * **D. Rheumatic fever:** This is a non-suppurative sequela of **Group A Streptococcal (GAS)** pharyngitis, involving an autoimmune cross-reactivity. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication overall:** Paralytic ileus. * **Most serious/dreaded complications:** Intestinal perforation and hemorrhage (typically occur in the 3rd week) [1]. * **Pathognomonic finding:** Rose spots (faint pink macules on the trunk, seen in the 2nd week). * **Temperature-Pulse Dissociation:** Also known as **Faget’s sign** (relative bradycardia despite high fever). * **Investigation of choice:** * 1st week: Blood culture (highest sensitivity). * 2nd week: Widal test (though non-specific). * 3rd week: Stool/Urine culture. * **Overall most sensitive:** Bone marrow culture.

Q: Outright or full-blown AIDS is characterized by which of the following CD4 T-cell counts?

CD4 T-cell count < 200 cells/mm³. **Explanation:** The diagnosis of **AIDS (Acquired Immunodeficiency Syndrome)**, the advanced stage of HIV infection, is defined by the CDC based on two criteria: the presence of an AIDS-defining illness (e.g., Pneumocystis pneumonia, Kaposi sarcoma) or a **CD4+ T-lymphocyte count of < 200 cells/mm³**. **Why Option D is correct:** In a healthy adult, the normal CD4 count ranges from 500 to 1,500 cells/mm³. As HIV replicates, it progressively destroys CD4 cells. When the count drops below **200 cells/mm³**, the immune system is severely compromised, leading to "full-blown AIDS." At this threshold, the risk of life-threatening opportunistic infections increases exponentially. **Why other options are incorrect:** * **Options A & B (< 800 and < 600 cells/mm³):** These counts are often seen in the early or asymptomatic stages of HIV. While they represent a decline from the physiological peak, they do not meet the clinical definition of AIDS. * **Option C (< 400 cells/mm³):** While this indicates significant immune suppression and may warrant the initiation of certain prophylaxis, the official diagnostic cutoff for AIDS remains 200 cells/mm³. **High-Yield NEET-PG Pearls:** * **CD4 < 200:** Start prophylaxis for *Pneumocystis jirovecii* (Trimethoprim-Sulfamethoxazole). * **CD4 < 100:** High risk for *Toxoplasma gondii* and Cryptococcosis. * **CD4 < 50:** High risk for *Mycobacterium avium* complex (MAC) and CMV retinitis. * **Inversion of Ratio:** In HIV, the normal CD4:CD8 ratio (typically 2:1) is **reversed** (becomes < 1:1). * **Monitoring:** CD4 count is the best indicator of **immune status**, while Viral Load (HIV RNA) is the best predictor of **disease progression** and response to ART.

Q: A 30-year-old man with AIDS complains of severe pain on swallowing. Upper GI endoscopy shows elevated, white plaques on a hyperemic and edematous esophageal mucosa. Which of the following is the most likely diagnosis?

Candida esophagitis. ### Explanation **Correct Answer: B. Candida esophagitis** **Medical Concept:** In patients with HIV/AIDS, **Candida esophagitis** is the most common cause of infectious esophagitis and is an AIDS-defining illness [1]. The clinical hallmark is **odynophagia** (painful swallowing). Endoscopically, it presents as characteristic **adherent, elevated white plaques** (pseudomembranes) on an erythematous (hyperemic) and friable mucosa. These plaques cannot be easily washed away, and scraping them often reveals a raw, bleeding base. **Analysis of Incorrect Options:** * **A. Barrett esophagus:** This is a premalignant condition resulting from chronic GERD where squamous epithelium undergoes metaplasia to columnar epithelium. Endoscopy typically shows "salmon-pink" velvety mucosa, not white plaques. * **C. Herpetic esophagitis (HSV):** While common in AIDS, HSV typically presents with small, discrete, **"punched-out" stellate ulcers** (volcano-like). It does not present with elevated white plaques. * **D. Reflux esophagitis:** This is caused by gastric acid reflux. Endoscopic findings usually include linear erosions, streaks of erythema, or ulcerations in the distal esophagus, rather than diffuse white plaques. **NEET-PG High-Yield Pearls:** * **Most common cause of esophagitis in AIDS:** *Candida albicans*. * **Endoscopy vs. Symptoms:** If an AIDS patient has oral thrush and esophageal symptoms, empirical antifungal therapy (Fluconazole) is often started. Endoscopy is indicated if there is no response. * **Viral Differentials:** * **CMV Esophagitis:** Large, shallow, **linear ulcers** (Treatment: Ganciclovir). * **HSV Esophagitis:** Small, deep, **punched-out ulcers** (Treatment: Acyclovir). * **Microscopy:** Look for pseudohyphae and budding yeast on PAS or GMS stain.

Q: Which of the following clinical presentations does NOT qualify for the term "Severe Falciparum Malaria"?

High grade fever with rigors. **Explanation:** The definition of **Severe Falciparum Malaria** is based on the presence of clinical or laboratory evidence of vital organ dysfunction. According to the WHO criteria, severe malaria is a medical emergency characterized by complications that significantly increase the risk of mortality [1]. **Why Option D is Correct:** **High-grade fever with rigors** is a classic symptom of uncomplicated malaria [1]. While distressing to the patient, it does not indicate organ failure or a life-threatening complication. Therefore, it does not meet the criteria for "Severe Malaria." **Why the other options are Incorrect (Criteria for Severe Malaria):** * **Severe Anemia (Option A):** Defined as a hemoglobin concentration 5 mmol/L). This is often a result of microvascular sequestration leading to tissue hypoxia. * **Pulmonary Edema (Option C):** This is a grave complication (often presenting as ARDS) caused by increased capillary permeability or fluid overload, carrying a high mortality rate [1]. **NEET-PG High-Yield Pearls:** 1. **Drug of Choice:** For severe malaria, **Intravenous Artesunate** is the gold standard (superior to Quinine) [1]. 2. **Other Severe Criteria:** Hypoglycemia ( 3 mg/dL), and Jaundice (Bilirubin >3 mg/dL with parasite count >100,000/µL) [1]. 3. **Blackwater Fever:** Characterized by massive intravascular hemolysis and hemoglobinuria, leading to dark-colored urine.

Q: According to current criteria for Fever of Unknown Origin (FUO), what body temperature is considered significant?

101 F. ### Explanation The definition of **Fever of Unknown Origin (FUO)** was first standardized by Petersdorf and Beeson in 1961 and remains a cornerstone of clinical medicine. To qualify as FUO, a patient must meet specific criteria regarding temperature, duration, and diagnostic effort [1]. **Why Option D is Correct:** The classic and current criteria for FUO require a documented body temperature of **$\geq$ 101°F (38.3°C)** on several occasions. This threshold is set higher than the physiological "normal" (98.6°F) to exclude individuals with normal circadian temperature variations or low-grade habitual hyperthermia, ensuring that the diagnostic workup focuses on clinically significant pathology [1], [3]. **Analysis of Incorrect Options:** * **Option A (98.4°F):** This is considered a normal baseline body temperature. * **Option B (99.4°F):** While this may represent a "low-grade fever" in some clinical contexts, it does not meet the stringent threshold required for an FUO diagnosis. * **Option C (100°F):** This is often the threshold for defining a simple fever (pyrexia), but FUO criteria specifically require $\geq$ 101°F to increase diagnostic specificity [3]. **High-Yield NEET-PG Pearls:** * **The Three Criteria for FUO:** 1. **Temperature:** $\geq$ 101°F (38.3°C) on several occasions [1]. 2. **Duration:** Fever lasting for **> 3 weeks** [1]. 3. **Diagnostic Effort:** Failure to reach a diagnosis after **1 week** of inpatient investigation (or 3 outpatient visits in modern modified criteria) [1]. * **Etiology:** In adults, the most common causes of FUO are **Infections** (e.g., TB, Abscesses), followed by **Malignancies** (e.g., Lymphoma, RCC), and **Non-infectious Inflammatory Diseases** (e.g., Still’s disease, SLE) [1]. * **Factitious Fever:** Always consider this in patients with high temperatures but no tachycardia or sweating (dissociation of pulse and temperature) [2].

Question 1

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 2

What is the most common extrahepatic complication of amoebic hepatitis?

Accepted Answer

Lung abscess

Answer

Meningitis

Answer

Nephritis

Answer

Encephalitis

Question 3

A resident doctor sustained a needlestick injury while sampling blood of a patient who is HIV positive. A decision is taken to offer him post-exposure prophylaxis. Which one of the following would be the best recommendation?

Accepted Answer

Zidovudine + Lamivudine + Indinavir for 4 weeks

Answer

Zidovudine + Lamivudine for 4 weeks

Answer

Zidovudine + Lamivudine + Nevirapine for 4 weeks

Answer

Zidovudine + Stavudine + Nevirapine for 4 weeks

Question 4

A 50-year-old HIV-positive male presents with fever and breathlessness, diagnosed with Pneumocystis jiroveci pneumonia (PCP). At what CD4 T cell count is primary prophylaxis for PCP recommended?

Accepted Answer

< 200 cells/mm³

Answer

< 50 cells/mm³

Answer

< 150 cells/mm³

Answer

< 100 cells/mm³

Question 5

Regarding chronic hepatitis B, all of the following are true EXCEPT:

Accepted Answer

Chronicity if infected in adulthood is about 10%.

Answer

There is a 90% chance for chronic infection if infected at birth.

Answer

Mild chronic hepatitis B has a 5-year survival of 97%.

Answer

Adult infection is usually symptomatic.

Question 6

What is the most common complication of Typhoid fever?

Accepted Answer

Paralytic ileus

Answer

Otitis media

Answer

Oophoritis

Answer

Rheumatic fever

Question 7

Outright or full-blown AIDS is characterized by which of the following CD4 T-cell counts?

Accepted Answer

CD4 T-cell count < 200 cells/mm³

Answer

CD4 T-cell count < 800 cells/mm³

Answer

CD4 T-cell count < 600 cells/mm³

Answer

CD4 T-cell count < 400 cells/mm³

Question 8

A 30-year-old man with AIDS complains of severe pain on swallowing. Upper GI endoscopy shows elevated, white plaques on a hyperemic and edematous esophageal mucosa. Which of the following is the most likely diagnosis?

Accepted Answer

Candida esophagitis

Answer

Barrett esophagus

Answer

Herpetic esophagitis

Answer

Reflux esophagitis

Question 9

Which of the following clinical presentations does NOT qualify for the term "Severe Falciparum Malaria"?

Accepted Answer

High grade fever with rigors

Answer

Severe anemia

Answer

Acidosis

Answer

Pulmonary edema

Question 10

According to current criteria for Fever of Unknown Origin (FUO), what body temperature is considered significant?

Accepted Answer

101
F

Answer

98.4
F

Answer

99.4
F

Answer

100
F

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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