Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1081: A 40-year-old man who recently traveled to South America presents with a chronic, ulcerative lesion on his arm. A biopsy reveals amastigotes within macrophages. What is the most likely diagnosis?

A. Cutaneous leishmaniasis (Correct Answer)
B. Cutaneous tuberculosis
C. Sporotrichosis
D. Mycetoma

Explanation: ### Cutaneous leishmaniasis - The patient's recent travel to **South America**, a region endemic for Leishmaniasis, combined with a chronic, **ulcerative lesion** and the presence of **amastigotes within macrophages** on biopsy, are classic diagnostic features [1]. - Amastigotes are the non-motile, intracellular form of Leishmania parasites found in human tissues [1]. *Cutaneous tuberculosis* - While it can manifest as chronic ulcerative lesions, the biopsy would show **granulomas with caseation necrosis** containing acid-fast bacilli, not amastigotes within macrophages. - Diagnosis typically involves isolation of *Mycobacterium tuberculosis* or molecular tests, which is not described. *Sporotrichosis* - Characterized by **nodular lesions** that can ulcerate and spread along lymphatic channels, often associated with a history of **thorn prick** or contact with decaying vegetation. - Biopsy would reveal **cigar-shaped budding yeasts** (Sporothrix schenckii), not amastigotes within macrophages. *Mycetoma* - Presents as a chronic, destructive infection primarily affecting the **feet**, characterized by **swelling, sinuses, and grains** (macroscopic aggregates of microorganisms) being discharged. - Histology would show **granulomas with characteristic grains** (fungal hyphae or bacterial filaments), significantly different from amastigotes.

Question 1082: A 50-year-old patient presents with bloody diarrhea and a history of travel to India. Stool examination reveals trophozoites containing ingested red blood cells. What is the most likely diagnosis?

A. Giardiasis
B. Amoebiasis (Correct Answer)
C. Hookworm infection
D. Schistosomiasis

Explanation: Amoebiasis - The presence of **bloody diarrhea**, a history of **travel to India** (an endemic area) [1], and **trophozoites containing ingested red blood cells** are classic hallmarks of amoebiasis caused by **Entamoeba histolytica**. [2] - **E. histolytica** trophozoites invade the intestinal mucosa and consume red blood cells, leading to ulceration and bloody stools. Giardiasis - Characterized by **non-bloody, greasy, foul-smelling diarrhea**, abdominal cramps, and bloating. - Stool examination would typically reveal **Giardia lamblia trophozoites or cysts**, but not trophozoites with ingested red blood cells. Hookworm infection - Typically causes **iron deficiency anemia** due to chronic blood loss from the gut. [3] - While it can cause gastrointestinal symptoms, **bloody diarrhea** with trophozoites containing ingested red blood cells is not a characteristic finding. Schistosomiasis - Primarily causes symptoms related to the migration of **schistosome eggs** in various organs. - **Intestinal schistosomiasis** can lead to bloody diarrhea, but stool examination would show **schistosome eggs**, not amoebic trophozoites ingesting red blood cells.

Question 1083: A 60-year-old male with diabetes presents with fever, cough, and pleuritic chest pain. A chest X-ray reveals right lower lobe consolidation. What is the most appropriate initial antibiotic therapy?

A. Azithromycin
B. Amoxicillin
C. Levofloxacin
D. Ceftriaxone and azithromycin (Correct Answer)

Explanation: ***Ceftriaxone and azithromycin*** - This combination provides broad-spectrum coverage for **community-acquired pneumonia (CAP)**, targeting both typical bacteria (e.g., *Streptococcus pneumoniae*) and atypical pathogens (e.g., *Mycoplasma pneumoniae*, *Chlamydophila pneumoniae*) [1]. - Ceftriaxone is a **third-generation cephalosporin** effective against Gram-positive bacteria, while azithromycin is a **macrolide** covering atypical organisms and providing additional anti-inflammatory effects [2]. *Amoxicillin* - While effective against common pathogens like *Streptococcus pneumoniae*, **amoxicillin alone** may not adequately cover atypical pathogens or resistant strains, especially in patients with comorbidities like diabetes [3]. - It does not cover **atypical pneumonia**, which can be a significant cause of CAP. *Azithromycin* - Azithromycin is effective against **atypical pathogens** but does not provide sufficient coverage for common typical bacteria like *Streptococcus pneumoniae* when used as monotherapy in patients with comorbidities [2]. - Monotherapy with a macrolide like azithromycin is generally reserved for otherwise healthy individuals with **mild CAP**. *Levofloxacin* - Levofloxacin is a **respiratory fluoroquinolone** that offers broad-spectrum coverage, including typical and atypical pathogens, and can be used as monotherapy [2]. - However, due to concerns about increasing **antibiotic resistance** and potential side effects (e.g., QT prolongation, tendon rupture), it is often reserved for patients who cannot tolerate beta-lactams or macrolides, or in cases of severe CAP not responding to initial therapy.

Question 1084: A patient presents with diarrhea, bloating, and weight loss. Stool analysis shows pear-shaped, flagellated protozoa. What is the most likely diagnosis?

A. Amebiasis
B. Giardiasis (Correct Answer)
C. Ascariasis
D. Schistosomiasis

Explanation: Giardiasis - The classic presentation of diarrhea, bloating, and weight loss combined with the microscopic finding of pear-shaped, flagellated protozoa [1] in stool is pathognomonic for Giardia lamblia infection [1]. - Giardia trophozoites are easily identifiable by their distinctive morphology [1] and motility in fresh stool preparations. Amebiasis - Caused by Entamoeba histolytica, which typically presents with bloody diarrhea (dysentery) [2] and abdominal pain. - Trophozoites are larger, amoeboid, and lack flagella; they may contain ingested red blood cells. Ascariasis - This is an infection by a roundworm (Ascaris lumbricoides), a multicellular parasite, not a single-celled protozoan. - Symptoms can include abdominal pain, malnutrition, or pulmonary involvement during larval migration, but pear-shaped flagellated protozoa would not be seen. Schistosomiasis - Caused by a fluke (Schistosoma species), a type of flatworm, which is also a multicellular parasite, not a protozoan. - Symptoms vary depending on the species and stage of infection but often involve urinary or intestinal inflammation and are diagnosed by finding eggs (not flagellated protozoa) in stool or urine.

Question 1085: Which test is most appropriate for diagnosing Clostridium difficile infection in a patient presenting with diarrhea after antibiotic use?

A. Stool culture
B. CT scan of the abdomen
C. Serum electrolytes
D. Stool PCR for C. difficile toxin (Correct Answer)

Explanation: ***Stool PCR for C. difficile toxin*** - A **stool PCR test** is highly sensitive and specific for detecting the presence of the *C. difficile* pathogen and/or its **toxin genes**, making it the most appropriate and rapid diagnostic method [2]. - This test identifies the **DNA of *C. difficile*** and/or its toxin genes (**tcdA** and **tcdB**), which are responsible for the severe diarrhea and colitis [2]. *Stool culture* - While stool culture can identify *C. difficile*, it has **lower specificity** because asymptomatic carriers can also harbor the bacteria [1]. - Culture is also **time-consuming** (2-3 days), which can delay crucial treatment for *C. difficile* infection. *CT scan of the abdomen* - A **CT scan** is not a primary diagnostic tool for *C. difficile* infection but can be used to assess for complications like **toxic megacolon** or **colonic perforation** in severe cases [1]. - It does not directly identify the presence of the pathogen or its toxins, so it's not the initial diagnostic test for the infection itself. *Serum electrolytes* - **Serum electrolytes** are important for monitoring the patient's hydration status and detecting imbalances caused by severe diarrhea (e.g., **hypokalemia**, **hyponatremia**). - However, they do not diagnose the underlying cause of the diarrhea, which in this case is suspected *C. difficile* infection.

Question 1086: Which organ system is primarily affected by the yellow fever virus, leading to its characteristic symptoms?

A. Liver (Correct Answer)
B. Lungs
C. Kidneys
D. Heart

Explanation: ***Liver*** - The **yellow fever virus** primarily targets and replicates within **hepatocytes**, leading to **hepatic necrosis** and dysfunction. - This liver damage causes the characteristic **jaundice** (yellowing of skin and eyes) due to impaired bilirubin metabolism. *Lungs* - While respiratory symptoms can occur in severe cases due to systemic inflammation or secondary infections, the **lungs are not the primary target organ** of the yellow fever virus. - **Pneumonia** or **acute respiratory distress syndrome (ARDS)** may develop as complications, but not as the initial and defining feature of the disease. *Kidneys* - **Kidney failure** can be a severe complication of yellow fever, often due to **hypotension**, **hemorrhage**, and **multi-organ dysfunction syndrome**. - However, the kidneys are **secondarily affected** by the systemic illness rather than being the primary site of viral replication and damage. *Heart* - Myocardial involvement, such as **myocarditis**, can occur in severe yellow fever cases and contribute to **cardiac dysfunction** and **shock**. - Similar to the kidneys, the heart is typically **not the primary organ** directly targeted by the virus, but rather affected by the systemic inflammatory response and organ damage.

Question 1087: What is the most common cause of sepsis?

A. Bacterial infections (Correct Answer)
B. Viral infections
C. Fungal infections
D. Parasitic infections

Explanation: ***Bacterial infections*** - The vast majority of sepsis cases are triggered by **bacterial infections**, with common culprits including *Staphylococcus aureus*, *Escherichia coli*, and *Streptococcus pneumoniae* [1]. - These bacteria can originate from various sites such as the lungs (pneumonia), urinary tract (urosepsis), abdomen, and skin [1]. *Viral infections* - While viral infections can sometimes lead to sepsis, they are a **less common cause** than bacterial infections. - Examples include severe influenza or COVID-19, but they typically lead to a septic response much less frequently than bacteria. *Fungal infections* - Fungal infections, particularly *Candida* species, can cause sepsis, especially in **immunocompromised individuals** or those with prolonged hospitalization [1]. - However, they are significantly less common as a primary cause of sepsis compared to bacteria. *Parasitic infections* - Parasitic infections are a **rare cause of sepsis** in most developed regions, though opportunistic infections can occur in immunocompromised patients [1]. - Examples like severe malaria can lead to a systemic inflammatory response, but they are not among the most common global causes of sepsis [1].

Question 1088: A 32-year-old woman is advised on post-exposure prophylaxis (PEP) following a needlestick injury. What is the recommended regimen for HIV PEP?

A. Single drug regimen
B. Two-drug regimen
C. Three-drug regimen (Correct Answer)
D. Four-drug regimen

Explanation: ***Three-drug regimen*** - A **three-drug regimen** is the **standard recommendation** for effective HIV post-exposure prophylaxis (PEP) to maximize the chances of preventing infection. - This approach typically involves a combination of two **nucleoside reverse transcriptase inhibitors (NRTIs)** and one **integrase strand transfer inhibitor (INSTI)** or a **protease inhibitor (PI)** [1]. *Single drug regimen* - A **single-drug regimen** is generally **insufficient** for preventing HIV infection after a significant exposure due to the risk of viral resistance and lower efficacy. - This approach would **not meet current guidelines** for optimal post-exposure prophylaxis. *Two-drug regimen* - While a **two-drug regimen** might be considered in very low-risk exposures or in situations where a three-drug regimen is contraindicated, it is **not the preferred standard**. - The **efficacy is lower** compared to a three-drug regimen, especially when the source virus's resistance profile is unknown or the exposure risk is moderate to high [1]. *Four-drug regimen* - A **four-drug regimen** is **not routinely recommended** for HIV PEP as there is no evidence that adding a fourth drug significantly improves efficacy over a three-drug regimen. - It would increase the risk of **drug-related toxicities and side effects** without additional benefit in most cases.

Question 1089: A 30-year-old woman with recent travel to Southeast Asia presents with an eschar at the site of a chigger bite and a febrile illness. What is the most appropriate initial treatment?

A. Doxycycline (Correct Answer)
B. Azithromycin
C. Ciprofloxacin
D. Amoxicillin

Explanation: ***Doxycycline*** - This presentation is highly suggestive of **scrub typhus**, an infectious disease endemic to Southeast Asia, characterized by a **febrile illness** and an **eschar** at the site of a chigger bite. - **Doxycycline** is the drug of choice for treating scrub typhus, as well as other rickettsial infections, due to its efficacy against *Orientia tsutsugamushi*. *Azithromycin* - While azithromycin can be used as an alternative for scrub typhus, particularly in pregnant women or young children, it is **less effective** than doxycycline, especially in severe cases. - It is typically considered when doxycycline is contraindicated. *Ciprofloxacin* - Ciprofloxacin is a **fluoroquinolone antibiotic** that is generally not effective against *Orientia tsutsugamushi* or other rickettsial infections. - It targets bacterial DNA gyrase and topoisomerase IV, mechanisms that are not crucial for eradicating this specific pathogen. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic that is ineffective against atypical bacteria like *Orientia tsutsugamushi* because it targets bacterial cell wall synthesis which is not a primary mechanism of action against rickettsial organisms. - It would not be an appropriate treatment for scrub typhus.

Question 1090: A 25-year-old woman presents with fever, rash, and joint pain after returning from Southeast Asia. What is the most likely diagnosis?

A. Dengue fever (Correct Answer)
B. Malaria
C. Typhoid fever
D. Leptospirosis

Explanation: ***Dengue fever*** - The classic triad of **fever**, **rash**, and **arthralgia** (joint pain) following travel to endemic areas like Southeast Asia is highly suggestive of dengue [1]. - Dengue is a **mosquito-borne viral infection** common in tropical and subtropical regions. *Malaria* - Characterized by **cyclic fevers**, chills, and sweats [2], but rash and prominent joint pain are not typical features. - Diagnosed by **microscopic examination** of blood smears for parasites or rapid diagnostic tests. *Typhoid fever* - Presents with a **prolonged fever**, headache, abdominal pain, and often a **"rose spot" rash**, but significant joint pain is uncommon. - Caused by **Salmonella Typhi** and transmitted through contaminated food or water. *Leptospirosis* - Typically causes **fever**, headache, muscle pain (myalgia), and sometimes jaundice, but a widespread rash and prominent arthralgia are less characteristic. - Transmitted through contact with **urine of infected animals** or contaminated water.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

Practice Questions

Antimicrobial Resistance

Practice Questions

Vaccination Principles

Practice Questions

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