Infectious Diseases — MCQs

A 40-year-old female with systemic lupus erythematosus on chronic steroids presents with fever, cough, and shortness of breath. Chest X-ray shows bilateral infiltrates. Laboratory results indicate a white blood cell count of 2,000 and a PaO2 of 60 on room air. What is the best therapeutic approach for this patient?

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1081: A 28-year-old man presents with fever, chills, and a rash that began on the wrists and ankles and spread to the trunk. What is the most likely diagnosis?

A. Rocky Mountain spotted fever (Correct Answer)
B. Lyme disease
C. Measles
D. Meningococcemia

Explanation: ***Rocky Mountain spotted fever*** - The classic presentation involves **fever, chills**, and a **rash** that starts on the **wrists and ankles** and spreads centrally to the trunk [1]. - This is a **tick-borne illness** caused by *Rickettsia rickettsii*, a highly suggestive clinical picture [1]. *Lyme disease* - Characterized by an expanding **erythema migrans** (bull's-eye rash), which is typically large and annular, not a diffuse rash spreading from extremities. - While it can cause fever and chills, the rash morphology and spread pattern are inconsistent with this case description. *Measles* - Presents with a **maculopapular rash** that typically starts on the **face** and spreads downwards to the trunk and extremities, not initiating on the wrists and ankles. - Associated with the "3 Cs": **cough, coryza, and conjunctivitis**, and possibly **Koplik spots**, which are not mentioned. *Meningococcemia* - Often presents with an abrupt onset of **fever, headache, stiff neck**, and a **petechial or purpuric rash**, which does not typically start on the wrists and ankles. - The rash is usually diffuse and can rapidly progress to **purpura fulminans**, often indicating severe sepsis.

Question 1082: A 25-year-old woman presents with a severe sore throat, fever, and difficulty swallowing. Examination reveals swollen tonsils with white exudate and tender cervical lymphadenopathy. What is the most likely diagnosis?

A. Viral pharyngitis
B. Streptococcal pharyngitis (Correct Answer)
C. Epstein-Barr virus infection
D. Diphtheria

Explanation: Streptococcal pharyngitis - The combination of severe sore throat, fever, swollen tonsils with white exudate, and tender cervical lymphadenopathy is highly suggestive of Group A Streptococcus (GAS) infection. - This clinical presentation aligns with the Centor criteria for diagnosing strep throat, which includes tonsillar exudates, tender anterior cervical lymph nodes, absence of cough, and history of fever. Viral pharyngitis - While viral pharyngitis can cause sore throat and fever, it often presents with additional symptoms like cough, rhinorrhea (runny nose), and conjunctivitis, which are absent here. - White exudates on the tonsils are less common and typically not as prominent in viral cases compared to bacterial infections. Epstein-Barr virus infection - Infectious mononucleosis due to EBV can present with severe pharyngitis, exudative tonsillitis, fever, and lymphadenopathy, but it often includes fatigue, splenomegaly, and atypical lymphocytosis, which are not mentioned in this case. - While it's a possibility, the classic presentation without other distinguishing features makes streptococcal pharyngitis more likely. Diphtheria - Diphtheria is characterized by a greyish-white pseudomembrane that is firmly attached to the tonsils and pharynx and bleeds if scraped, which is not described [1]. - This disease is now rare due to vaccination and typically involves more systemic toxicity and potential airway obstruction [1].

Question 1083: 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 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: 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 1087: 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 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 40-year-old female with systemic lupus erythematosus on chronic steroids presents with fever, cough, and shortness of breath. Chest X-ray shows bilateral infiltrates. Laboratory results indicate a white blood cell count of 2,000 and a PaO2 of 60 on room air. What is the best therapeutic approach for this patient?

A. Empiric broad-spectrum abx + IVIG
B. Plasma exchange + supportive care
C. Broad-spectrum abx + granulocyte colony-stimulating factor (G-CSF)
D. TMP-SMX + corticosteroids (Correct Answer)

Explanation: ***TMP-SMX + corticosteroids*** - The patient's presentation (**fever, cough, shortness of breath, bilateral infiltrates, low WBC, hypoxemia**) in a patient with **SLE on chronic steroids** strongly suggests **Pneumocystis jirovecii pneumonia (PJP)** [1]. - **Trimethoprim-sulfamethoxazole (TMP-SMX)** is the first-line treatment for PJP, and **corticosteroids** are indicated for moderate to severe PJP (PaO2 < 70 mmHg or A-a gradient > 35 mmHg) to mitigate inflammatory lung damage [1]. *Empiric broad-spectrum abx + IVIG* - While empiric broad-spectrum antibiotics might be considered for unknown infections, **PJP is highly suspected** given the patient's immunosuppression [3], making targeted therapy with TMP-SMX more appropriate. - **Intravenous immunoglobulin (IVIG)** is typically used for antibody deficiencies or autoimmune disorders and has no primary role in treating PJP. *Plasma exchange + supportive care* - **Plasma exchange** is used to remove harmful antibodies or immune complexes, primarily in severe autoimmune flares or conditions like thrombotic thrombocytopenic purpura [4], not for infectious pulmonary infiltrates. - While supportive care is always necessary, it's insufficient alone to treat a potentially life-threatening infection like PJP. *Broad-spectrum abx + granulocyte colony-stimulating factor (G-CSF)* - **Broad-spectrum antibiotics** alone are not effective against *Pneumocystis jirovecii*, which is a fungus, not bacteria [1]. - **G-CSF** is used to stimulate neutrophil production, beneficial in severe neutropenia [2], but not a primary treatment for PJP or the underlying cause of lung infiltrates in this scenario.

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

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Antimicrobial Resistance

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Vaccination Principles

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