Infectious Diseases Practice Questions

Q: A 55-year-old man presents with fever, chills, and hematuria. He has a history of travel to sub-Saharan Africa, and a blood smear shows schistosomes. What is the most likely diagnosis?

Schistosomiasis. Schistosomiasis - The presence of schistosomes on a blood smear directly confirms the diagnosis of schistosomiasis. - Hematuria is a classic symptom, particularly with Schistosoma haematobium infection which is common in sub-Saharan Africa [1]. Malaria - Characterized by periodic fevers, chills, and sweats [2], but the blood smear would show Plasmodium parasites, not schistosomes. - While common in sub-Saharan Africa, the specific finding of schistosomes rules out malaria as the primary diagnosis [2]. Leptospirosis - Presents with fever, chills, headache, muscle pain, and can involve renal dysfunction [3], but is caused by bacteria (Leptospira species), not parasites. - Diagnosis is typically by serology or PCR, and blood smears would not show schistosomes. Typhoid fever - Symptoms include sustained fever, headache, abdominal pain, and sometimes rash, caused by Salmonella Typhi bacteria. - Diagnosis is made by blood or stool cultures, and it does not involve hematuria or schistosomes on a blood smear.

Q: A patient presents with an acute onset of severe muscle pain, fever, and headache after hiking in the woods. Blood tests reveal elevated creatine kinase levels. What is the most likely diagnosis?

Leptospirosis. ***Leptospirosis*** - The triad of **acute onset muscular pain**, **fever**, and **headache** after outdoor exposure (hiking) strongly suggests leptospirosis [1]. - **Elevated creatine kinase** indicates muscle involvement, common in severe leptospirosis due to myositis [1]. *Lyme disease* - Characterized by an expanding **erythema migrans** rash, which is not mentioned. - While it can cause muscle aches, elevated CK is not a typical or prominent finding. *Rocky Mountain spotted fever* - Typically presents with a **maculopapular rash** that begins on the ankles and wrists and spreads centrally, which is absent. - Although it causes fever and muscle pain, elevated CK is not as characteristic as in leptospirosis. *Trichinosis* - Acquired through ingestion of **undercooked meat** (especially pork or wild game), not typically from hiking in the woods. - Primarily causes **muscle pain** due to larval migration and can elevate CK, but the history of exposure differs.

Q: A 40-year-old patient with a history of intravenous drug use presents with fever and a new heart murmur. Blood cultures grow gram-positive cocci in chains. What is the most likely organism?

Streptococcus viridans. ***Streptococcus viridans*** - While *S. aureus* is the most common cause of **infective endocarditis** in IV drug users, *Streptococcus viridans* is often associated with the **oropharyngeal flora** and can cause subacute bacterial endocarditis [1]. - The description "gram-positive cocci in chains" is consistent with *Streptococcus* species. *Staphylococcus aureus* - This is the **most common cause** of infective endocarditis in intravenous drug users, often affecting the **tricuspid valve** [1]. - However, *Staphylococcus aureus* typically grows as **ग्राम-positive cocci in clusters**, not chains. *Enterococcus faecalis* - *Enterococcus faecalis* can cause endocarditis, especially in **older patients** with genitourinary or gastrointestinal procedures [1]. - While it's gram-positive cocci, it's less commonly seen in the context of IV drug use compared to *Staphylococcus aureus* or *Streptococcus viridans*. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is a common cause of **pneumonia** and **meningitis**, but it is a relatively rare cause of endocarditis [1]. - Although it is a gram-positive coccus, it typically appears in **pairs (diplococci)** or short chains, and its association with endocarditis in IV drug users is not primary.

Q: A 32-year-old patient presents with a non-healing ulcer on the leg. Which bacterial infection should be suspected, particularly in a diabetic patient?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Diabetic patients** are particularly susceptible to **Staphylococcus aureus** infections, which commonly cause **skin and soft tissue infections**, including non-healing ulcers [1]. - **Diabetic ulcers** provide an entry point for bacteria, and **S. aureus** is a frequent colonizer and pathogen in these wounds due to impaired immune function and peripheral vascular disease in diabetics [1], [2]. *Streptococcus pyogenes* - While **Streptococcus pyogenes** can cause skin infections (e.g., cellulitis, erysipelas), it is less frequently associated with **non-healing ulcers** in diabetic patients compared to S. aureus. - S. pyogenes infections often present with more rapid progression and distinct spreading erythema. *Clostridium perfringens* - **Clostridium perfringens** primarily causes **gas gangrene** (clostridial myonecrosis), a severe, rapidly progressing infection characterized by gas production in tissues, an acute onset, and systemic toxicity. - It is typically a deep tissue infection following trauma or surgery, not a common cause of superficial non-healing ulcers. *Pseudomonas aeruginosa* - **Pseudomonas aeruginosa** is often associated with infections in **burn wounds**, **ventilator-associated pneumonia**, and infections in immunocompromised individuals. - While it can infect diabetic foot ulcers, it is typically seen in more chronic, established wounds or those with specific exposures (e.g., aquatic environments) and is less universally implicated as the primary cause of non-healing ulcers in newly presenting diabetics than S. aureus.

Q: A 25-year-old male patient presents with jaundice, dark urine, and elevated liver enzymes. He tests positive for HBsAg and HBeAg. What is the most appropriate treatment?

Tenofovir. ***Tenofovir*** - This patient presents with **acute hepatitis B** (jaundice, dark urine, elevated liver enzymes, HBsAg, HBeAg), indicating active viral replication [1]. **Tenofovir** is a highly effective **nucleotide analog reverse transcriptase inhibitor** used to treat chronic HBV infection, and can be used in severe acute cases or those at risk of chronicity [1]. - It works by inhibiting the **HBV reverse transcriptase**, thereby reducing viral load and preventing liver damage. *Acyclovir* - **Acyclovir** is an antiviral medication specifically used to treat **herpes simplex virus (HSV)** and **varicella-zoster virus (VZV)** infections [3]. - It has no activity against the **hepatitis B virus (HBV)**, making it ineffective for this patient's condition [3]. *Ribavirin* - **Ribavirin** is an antiviral drug primarily used in combination with other agents, such as interferon, for the treatment of **hepatitis C virus (HCV)** infection. - It is **not effective** against the hepatitis B virus and is not indicated for the management of acute or chronic HBV. *Interferon-alpha* - **Interferon-alpha** is an immunomodulatory agent that can be used to treat both chronic **hepatitis B** and **hepatitis C** infections [2]. - However, for acute severe hepatitis B, **nucleoside/nucleotide analogs like tenofovir** are generally preferred due to better tolerability and higher antiviral efficacy in rapidly reducing viral replication [1].

Q: A 70-year-old man with a history of diabetes presents with a non-healing ulcer on his foot. Upon examination, there is a foul smell and black necrotic tissue. What complication has most likely developed in this ulcer?

Infection. Infection - Foul smell and black necrotic tissue are classic signs of severe infection, often involving anaerobic bacteria, leading to gangrene [1]. - In diabetic foot ulcers, impaired immune response and peripheral neuropathy increase susceptibility to infection, which can rapidly progress and lead to tissue death [1]. Arterial insufficiency - While arterial insufficiency is a common underlying cause of diabetic foot ulcers and can contribute to non-healing, the presence of a foul smell and black necrotic tissue specifically points to superimposed infection and tissue death (gangrene) [1]. - Arterial insufficiency primarily causes ischemia and non-healing due to lack of blood supply, not directly the foul smell unless secondary infection occurs [2]. Diabetic neuropathy - Diabetic neuropathy leads to loss of sensation and can cause painless ulcers due to repetitive trauma, often at pressure points [1]. - While it is a primary factor in ulcer formation, it does not directly cause the foul smell or black necrotic tissue; these are indicators of infection and tissue necrosis [1]. Venous insufficiency - Venous insufficiency typically results in ulcers around the ankles (gaiter area) with characteristic findings like edema, hyperpigmentation, and lipodermatosclerosis [2]. - These ulcers are often wet and exudative but do not usually present with a foul smell and black necrotic tissue unless complicated by severe, unmanaged infection, which is not the primary feature of venous ulcers [2].

Q: A patient presents with a chronic non-healing ulcer on the foot. Culture reveals the growth of a dimorphic fungus. Which of the following is the most likely diagnosis?

Sporotrichosis. ***Sporotrichosis*** - **Sporotrichosis** is characterized by subcutaneous nodules and **non-healing ulcers**, often following **thorn pricks** or other trauma, particularly in gardeners. - The fungus **_Sporothrix schenckii_** is dimorphic, growing as a mold in the environment and as a yeast in human tissue at body temperature. *Candidiasis* - **Candidiasis** typically presents as **mucocutaneous infections** (e.g., thrush, vaginitis, diaper rash) or systemic infections in immunocompromised individuals [1]. - While _Candida_ is a yeast, it is not dimorphic in the same way as the fungi causing deep mycoses, and chronic non-healing ulcers on the foot are not its typical presentation unless associated with severe immunosuppression [1]. *Histoplasmosis* - **Histoplasmosis** primarily affects the **lungs** following inhalation of spores from bird or bat droppings, leading to pneumonia-like symptoms or disseminated disease in immunocompromised patients. - While _Histoplasma capsulatum_ is a dimorphic fungus, localized cutaneous ulcers are rare and usually occur as part of disseminated disease, not as an isolated foot ulcer. *Blastomycosis* - **Blastomycosis** can cause **cutaneous lesions**, including ulcers and verrucous (wart-like) lesions, in addition to pulmonary and disseminated disease. - However, it is less commonly associated with the specific "non-healing ulcer on the foot" scenario compared to sporotrichosis, which often involves local inoculation and lymphatic spread.

Q: What is the most effective therapy for preventing vertical transmission of HIV from a pregnant woman to her fetus?

Zidovudine administration. ***Zidovudine administration*** - **Zidovudine (AZT)** is a **nucleoside reverse transcriptase inhibitor** that significantly reduces the viral load in the mother and prevents HIV transmission to the fetus. - Administering zidovudine during pregnancy, labor, and to the newborn infant post-delivery is a cornerstone of **preventing mother-to-child transmission (PMTCT)** of HIV. *Cesarean delivery* - While recommended in specific cases, such as high maternal viral load, **cesarean delivery alone** is less effective than antiretroviral therapy in preventing vertical transmission [1]. - The primary benefit of cesarean delivery is to prevent exposure to maternal blood and genital secretions during vaginal birth. *High-dose vitamin supplementation* - **Vitamin supplementation** is important for maternal and fetal health overall but has **no direct proven effect** on preventing vertical HIV transmission. - There is no evidence suggesting it reduces viral load or blocks virus transfer. *Prophylactic antibiotics* - **Prophylactic antibiotics** are used to prevent bacterial infections but have **no antiviral activity** against HIV. - They do not reduce the risk of vertical HIV transmission.

Q: A patient presents with worsening respiratory distress following a bone marrow transplant. A chest CT reveals diffuse, bilateral, ground-glass opacities. Gomori methenamine silver stain of bronchoalveolar lavage fluid shows cup-shaped yeast forms. What is the probable diagnosis?

Pneumocystis jirovecii pneumonia. ***Pneumocystis jirovecii pneumonia*** - The combination of **worsening respiratory distress** in an immunocompromised patient (post-bone marrow transplant), **diffuse bilateral ground-glass opacities** on CT, and **cup-shaped yeast forms** on Gomori methenamine silver (GMS) stain of BAL fluid is pathognomonic for **Pneumocystis jirovecii pneumonia (PJP)** [1]. - PJP is an **opportunistic fungal infection** common in severely immunocompromised individuals, characteristically presenting with these radiological and microscopic findings [1]. *Cryptococcus neoformans infection* - **Cryptococcus neoformans** typically presents with **meningitis** or pulmonary nodules/masses, not diffuse ground-glass opacities. - While it can manifest in immunocompromised patients, microscopic examination reveals **encapsulated yeast cells** that stain with India ink, not cup-shaped forms with GMS. *Candida albicans pneumonia* - **Candida albicans** can cause pneumonia in severely immunocompromised patients, but it usually presents as **bronchopneumonia** or **abscesses**, not diffuse ground-glass opacities. - Microscopically, Candida appears as **budding yeast with pseudohyphae**, which are distinct from the cup-shaped forms seen in PJP. *Aspergillus fumigatus infection* - **Aspergillus fumigatus** in immunocompromised patients commonly causes **invasive aspergillosis**, presenting clinically with **fever**, **cough**, and **hemoptysis**. - Radiologically, it often presents with **nodules**, **cavitation**, or the **halo sign**, distinguishing it from the diffuse ground-glass opacities seen in PJP. Microscopy would show **septate hyphae with acute angle branching**.

Q: A 40-year-old man with HIV presents with a cough and low-grade fever. A chest X-ray shows diffuse interstitial infiltrates. What is the most likely pathogen?

Pneumocystis jirovecii. ***Pneumocystis jirovecii*** - **Pneumocystis pneumonia (PCP)** is an opportunistic infection common in individuals with **HIV**, especially when their **CD4 count is low**. [1] - The classic presentation includes **cough**, **low-grade fever**, and **diffuse interstitial infiltrates** on chest X-ray. [1] *Streptococcus pneumoniae* - While **Streptococcus pneumoniae** can cause pneumonia in HIV patients, it typically presents with **lobar consolidation** rather than diffuse interstitial infiltrates. - Patients usually experience a **sudden onset of high fever**, productive cough, and pleuritic chest pain. [2] *Haemophilus influenzae* - **Haemophilus influenzae** can cause community-acquired pneumonia, but it is not typically associated with **diffuse interstitial infiltrates** in HIV patients. - It often leads to **bronchopneumonia** or lobar pneumonia. *Mycoplasma pneumoniae* - **Mycoplasma pneumoniae** causes "walking pneumonia," which can present with interstitial infiltrates, but is generally a **milder disease** and less common as a severe opportunistic infection in advanced HIV. - It often causes **extrapulmonary symptoms** like pharyngitis and bullous myringitis.

Question 1

A 55-year-old man presents with fever, chills, and hematuria. He has a history of travel to sub-Saharan Africa, and a blood smear shows schistosomes. What is the most likely diagnosis?

Accepted Answer

Schistosomiasis

Answer

Malaria

Answer

Leptospirosis

Answer

Typhoid fever

Question 2

A patient presents with an acute onset of severe muscle pain, fever, and headache after hiking in the woods. Blood tests reveal elevated creatine kinase levels. What is the most likely diagnosis?

Accepted Answer

Leptospirosis

Answer

Lyme disease

Answer

Rocky Mountain spotted fever

Answer

Trichinosis

Question 3

A 40-year-old patient with a history of intravenous drug use presents with fever and a new heart murmur. Blood cultures grow gram-positive cocci in chains. What is the most likely organism?

Accepted Answer

Streptococcus viridans

Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Enterococcus faecalis

Question 4

A 32-year-old patient presents with a non-healing ulcer on the leg. Which bacterial infection should be suspected, particularly in a diabetic patient?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Clostridium perfringens

Answer

Pseudomonas aeruginosa

Question 5

A 25-year-old male patient presents with jaundice, dark urine, and elevated liver enzymes. He tests positive for HBsAg and HBeAg. What is the most appropriate treatment?

Accepted Answer

Tenofovir

Answer

Acyclovir

Answer

Ribavirin

Answer

Interferon-alpha

Question 6

A 70-year-old man with a history of diabetes presents with a non-healing ulcer on his foot. Upon examination, there is a foul smell and black necrotic tissue. What complication has most likely developed in this ulcer?

Accepted Answer

Infection

Answer

Arterial insufficiency

Answer

Diabetic neuropathy

Answer

Venous insufficiency

Question 7

A patient presents with a chronic non-healing ulcer on the foot. Culture reveals the growth of a dimorphic fungus. Which of the following is the most likely diagnosis?

Accepted Answer

Sporotrichosis

Answer

Candidiasis

Answer

Histoplasmosis

Answer

Blastomycosis

Question 8

What is the most effective therapy for preventing vertical transmission of HIV from a pregnant woman to her fetus?

Accepted Answer

Zidovudine administration

Answer

Cesarean delivery

Answer

High-dose vitamin supplementation

Answer

Prophylactic antibiotics

Question 9

A patient presents with worsening respiratory distress following a bone marrow transplant. A chest CT reveals diffuse, bilateral, ground-glass opacities. Gomori methenamine silver stain of bronchoalveolar lavage fluid shows cup-shaped yeast forms. What is the probable diagnosis?

Accepted Answer

Pneumocystis jirovecii pneumonia

Answer

Cryptococcus neoformans infection

Answer

Candida albicans pneumonia

Answer

Aspergillus fumigatus infection

Question 10

A 40-year-old man with HIV presents with a cough and low-grade fever. A chest X-ray shows diffuse interstitial infiltrates. What is the most likely pathogen?

Accepted Answer

Pneumocystis jirovecii

Answer

Streptococcus pneumoniae

Answer

Haemophilus influenzae

Answer

Mycoplasma pneumoniae

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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