Infectious Diseases Practice Questions

Q: According to current evidence and emerging guidelines, what is the preferred primary treatment for initial Clostridium difficile infection in adults?

Fidaxomicin. Fidaxomicin - **Fidaxomicin** is a macrocyclic antibiotic that has demonstrated superior sustained clinical response rates compared to vancomycin for initial episodes of *C. difficile* infection, especially in preventing recurrence. - Its **narrow spectrum of activity** minimizes disruption to the gut microbiome, which is crucial for preventing subsequent infections. *Metronidazole* - While previously used for mild-to-moderate *C. difficile* infection (CDI), **metronidazole** is no longer recommended as primary therapy due to its inferior efficacy compared to vancomycin or fidaxomicin [1]. - Its use is generally reserved for situations where **vancomycin or fidaxomicin are unavailable**, or in very specific, mild cases [1]. *Vancomycin* - **Oral vancomycin** is an effective treatment for *C. difficile* infection and was long considered a first-line option [1]. However, evidence suggests fidaxomicin may be superior, particularly in preventing recurrence. - It is still a highly effective treatment for CDI, especially for **initial episodes that are moderate to severe**, but fidaxomicin offers an advantage in sustained response. *Rifaximin* - **Rifaximin** is primarily used to prevent recurrence of *C. difficile* infection after an initial course of vancomycin, rather than as a primary treatment. - It is a **non-absorbable antibiotic** with limited utility as a standalone initial therapy for active CDI.

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 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 50-year-old male presents with a history of syphilis treated 10 years ago. He now complains of difficulty walking, lancinating pains in his legs, and urinary incontinence. What is the most likely diagnosis?

Tabes dorsalis. ***Tabes dorsalis*** - This is a late manifestation of **neurosyphilis** characterized by **demyelination of the dorsal columns** and dorsal roots of the spinal cord. - Clinical features such as **ataxia** (difficulty walking), **lancinating pains**, and **urinary incontinence** are classic symptoms resulting from sensory neurological damage. *Multiple sclerosis* - This is an **autoimmune demyelinating disease** affecting the central nervous system, which can cause motor and sensory deficits, including gait disturbances and urinary dysfunction. - However, there is no history of syphilis involvement and **lancinating pains** are less typical as the primary neurological complaint. *Diabetic neuropathy* - Can cause **sensory deficits** and pain, often in a **stocking-glove distribution**, along with autonomic dysfunction leading to urinary problems. - The patient's history of **syphilis** and the specific description of lancinating pains and ataxia are more indicative of tabes dorsalis, especially in the absence of a diabetes diagnosis. *Amyotrophic lateral sclerosis* - This is a **motor neuron disease** characterized by progressive muscle weakness, atrophy, and spasticity affecting both upper and lower motor neurons. - It does not typically present with the prominent **sensory symptoms** like lancinating pains or the specific gait ataxia described, and urinary incontinence is not a primary feature.

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.

Q: An HIV positive patient with a CD4 count of 300/cmm presents with mucosal lesions in the mouth. On microscopy, budding yeasts and pseudohyphae are seen. What is the most probable diagnosis?

Oral Candidiasis. ***Oral Candidiasis*** - The presence of **mucosal lesions** in the mouth of an **HIV-positive patient** with a **CD4 count of 300/cmm**, along with the microscopic finding of **budding yeasts and pseudohyphae**, is highly indicative of oral candidiasis. - This opportunistic fungal infection is common in immunocompromised individuals, and the microscopic appearance is pathognomonic for **Candida species**. *Oral Hairy Leukoplakia* - This condition is caused by the **Epstein-Barr virus (EBV)** and typically presents as white, corrugated, or "hairy" lesions, usually on the lateral borders of the tongue. - While common in HIV patients, it would not show **budding yeasts and pseudohyphae** on microscopy, as it is a viral infection. *Lichen Planus* - **Lichen Planus** is a chronic inflammatory condition affecting the skin and mucous membranes, often presenting as white, lacy patterns (Wickham's striae) or erosions. - It is an **immune-mediated disease** and does not involve fungal elements like yeasts and pseudohyphae. *Diphtheria* - **Diphtheria** is a bacterial infection caused by *Corynebacterium diphtheriae* that primarily affects the respiratory tract, leading to the formation of a **pseudomembrane** in the throat. - This disease is characterized by systemic toxicity and would not present with microscopic features of **budding yeasts and pseudohyphae** in oral lesions.

Q: A 45-year-old man presents with a clean minor wound from gardening. His vaccination record shows he completed primary tetanus immunization series in childhood and received his last tetanus booster 12 years ago. What is the next step in management?

Single-dose Tetanus toxoid (TT) vaccine. **Single-dose Tetanus toxoid (TT) vaccine** - For a **clean, minor wound** in a patient who has completed their primary series but received their last booster 12 years ago, a single dose of **tetanus toxoid (TT)** or **TDaP** is indicated [1]. - Booster doses are recommended every **10 years** for tetanus-diphtheria protection. *Tetanus Immunoglobulin (TIG) with TT booster.* - **Tetanus Immunoglobulin (TIG)** is typically reserved for **dirty or contaminated wounds**, or for individuals with an **uncertain or incomplete vaccination history**, which is not the case here. - Giving TIG for a clean wound with a complete primary series would be over-treatment and unnecessary. *No further management required.* - The patient's last booster was **12 years ago**, exceeding the recommended 10-year interval for tetanus protection. - This makes him susceptible to tetanus, even from a clean wound, so **further management is required** [1]. *Complete tetanus vaccination series.* - A **complete tetanus vaccination series** is only needed for individuals who have an **incomplete or unknown** primary vaccination history. - This patient has a documented history of a completed primary series, so only a booster dose is required.

Q: A bone marrow transplant recipient patient developed a chest infection. On HRCT, a 'tree-in-bud' appearance is seen. The most likely causative agent is:

TB. ***TB*** - A **'tree-in-bud' pattern** on HRCT is highly characteristic of **bronchiolar impaction** due to infection, classically seen in active **tuberculosis**. [1] - In an immunocompromised patient like a **bone marrow transplant recipient**, TB can rapidly disseminate and present with such radiographic findings. *Klebsiella* - **Klebsiella pneumonia** typically causes a **lobar pneumonia** with characteristic **bulging fissures** and severe consolidation. - It does not commonly present with a **'tree-in-bud' pattern** but rather extensive alveolar involvement. *Pneumocystis* - **Pneumocystis jirovecii pneumonia (PJP)** often presents with **diffuse ground-glass opacities** and **interstitial infiltrates**, predominantly in the perihilar region. [1] - A **'tree-in-bud' pattern** is not a typical radiographic feature of PJP. [1] *RSV* - **Respiratory Syncytial Virus (RSV)** typically causes **bronchiolitis** and **pneumonia**, especially in young children and immunocompromised adults. - While it can cause airway inflammation, a distinct **'tree-in-bud' pattern** is not its hallmark; rather, it often shows **peribronchial thickening** and **mucous plugging**.

Q: Which viral infection is known to resemble the clinical features of erythroblastosis?

Parvovirus B19. **Parvovirus B19** - Parvovirus B19 preferentially infects and destroys **erythroid progenitor cells** in the bone marrow, leading to varying degrees of anemia [1]. - In a fetus, this can manifest as **hydrops fetalis**, severe anemia, and **heart failure**, mirroring the severe hemolytic anemia seen in erythroblastosis fetalis caused by Rh incompatibility. *Epstein-Barr Virus (EBV)* - While EBV can cause various hematologic complications, it is not known to directly mimic the severe **erythroid aplasia** or hydrops fetalis associated with erythroblastosis. - EBV is primarily associated with **infectious mononucleosis**, which involves atypical lymphocytes and mild anemia, not destruction of red cell precursors. *Cytomegalovirus (CMV)* - CMV can cause **congenital infections** with a wide range of manifestations, including microcephaly, sensorineural hearing loss, and hepatosplenomegaly. - Although CMV can cause **anemia**, it does not typically cause the profound **erythroid aplasia** or hydrops that specifically resembles erythroblastosis. *Herpes Simplex Virus (HSV)* - HSV infection in neonates can cause severe disseminated disease, **encephalitis**, or localized skin, eye, and mouth disease. - HSV does not primarily target **erythroid precursors** or cause significant hemolytic anemia that would mimic erythroblastosis.

Question 1

According to current evidence and emerging guidelines, what is the preferred primary treatment for initial Clostridium difficile infection in adults?

Accepted Answer

Fidaxomicin

Answer

Rifaximin

Answer

Vancomycin

Answer

Metronidazole

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 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 4

A 50-year-old male presents with a history of syphilis treated 10 years ago. He now complains of difficulty walking, lancinating pains in his legs, and urinary incontinence. What is the most likely diagnosis?

Accepted Answer

Tabes dorsalis

Answer

Multiple sclerosis

Answer

Diabetic neuropathy

Answer

Amyotrophic lateral sclerosis

Question 5

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

Question 6

An HIV positive patient with a CD4 count of 300/cmm presents with mucosal lesions in the mouth. On microscopy, budding yeasts and pseudohyphae are seen. What is the most probable diagnosis?

Accepted Answer

Oral Candidiasis

Answer

Oral Hairy Leukoplakia

Answer

Lichen Planus

Answer

Diphtheria

Question 7

A 45-year-old man presents with a clean minor wound from gardening. His vaccination record shows he completed primary tetanus immunization series in childhood and received his last tetanus booster 12 years ago. What is the next step in management?

Accepted Answer

Single-dose Tetanus toxoid (TT) vaccine

Answer

No further management required.

Answer

Tetanus Immunoglobulin (TIG) with TT booster.

Answer

Complete tetanus vaccination series.

Question 8

A bone marrow transplant recipient patient developed a chest infection. On HRCT, a 'tree-in-bud' appearance is seen. The most likely causative agent is:

Accepted Answer

TB

Answer

Pneumocystis

Answer

Klebsiella

Answer

RSV

Question 9

Which viral infection is known to resemble the clinical features of erythroblastosis?

Accepted Answer

Parvovirus B19

Answer

Cytomegalovirus (CMV)

Answer

Epstein-Barr Virus (EBV)

Answer

Herpes Simplex Virus (HSV)

Question 10

Following are the features of neuropathy associated with varicella-zoster infection, which of the following is true?

Accepted Answer

Shingles are distributed along sensory dermatomes.

Answer

Upon reactivation, the virus is transported along sensory nerves to the skin, causing neuropathic symptoms.

Answer

Intranuclear inclusions, a hallmark of herpesvirus infections, are found in the peripheral nervous system during VZV neuropathy.

Answer

Persistent infection in neurons of sensory ganglia is a key feature of varicella-zoster virus pathophysiology.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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