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Infection, Pharmacology & VTE MCQs

Practice Set 3 of 68

This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 41

Topic: Infection, Pharmacology & VTE

Which of the following antibiotics would not be useful in staphylococcal vertebral osteomyelitis:

. C efuroxime
. Nafcillin
. C efazolin
. C iprofloxicin
. Tobramycin

Correct Answer & Explanation

. Tobramycin

Explanation

Aminoglycosides, such as tobramycin, are active against gram-negative organisms. First- and second-generation cephalosporins are alternatives to semisynthetic penicillins that may be useful if the organism is not resistant. Ciprofloxicin has also been considered a possible alternative to penicillins against gram-positive vertebral osteomyelitis.

Question 42

Topic: Infection, Pharmacology & VTE

A 55-year-old male with a history of intravenous drug use presents with severe midthoracic back pain. Gadolinium-enhanced MRI demonstrates epidural enhancement and high T2 signal within the T6-T7 disc space and adjacent endplates. What is the most common organism responsible for this condition?

. Pseudomonas aeruginosa
. Escherichia coli
. Staphylococcus aureus
. Enterococcus faecalis
. Klebsiella pneumoniae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus remains the most common causative organism of pyogenic spinal infections (discitis/osteomyelitis) across all patient groups, including intravenous drug users. Pseudomonas is a notable risk in the IVDU population, but S. aureus is still more frequent.

Question 43

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents with right hip pain, a limp, and a temperature of 38.8°C. He refuses to bear weight. His WBC is 13,000/mm³ and ESR is 45 mm/hr. According to the Kocher criteria, what is the probability that this child has septic arthritis rather than transient synovitis?
. < 5%
. 15%
. 40%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria include: non-weight-bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. Having 3 out of 4 criteria gives a 93% predictive probability for septic arthritis.

Question 44

Topic: Infection, Pharmacology & VTE

A 3-year-old boy presents with a temperature of 38.8 C, refusal to bear weight on his right leg, an ESR of 55 mm/hr, and a serum WBC of 14,000/mm3 with suspected hip pathology. According to Kocher criteria, what is the statistical probability of septic arthritis?

. 40%
. 55%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for septic arthritis of the hip include non-weight-bearing, temperature >38.5 C, ESR >40 mm/hr, and WBC >12,000/mm3. Having all 4 predictors yields a 99% probability of septic arthritis.

Question 45

Topic: Infection, Pharmacology & VTE

Which of the following toxins is responsible for the virulence of community- acquired methicillin-resistant Staphylococcus aureus (C A-MRSA):

. Beta-lactam
. Panton-Valentine leukocidin
. Oxazolidine
. mecA
. Streptolysin

Correct Answer & Explanation

. Panton-Valentine leukocidin

Explanation

Panton-Valentine leukocidin is a toxin that produces necrosis of tissue and white blood cells. This toxin is much more common in CA-MRSA than in hospital-acquired MRSA.

Question 46

Topic: Infection, Pharmacology & VTE

A 5-year-old girl presents to the emergency department with pain in her hip. Her temperature is 102° F, pulse is 96, and blood pressure is 104/60. Magnetic resonance imaging reveals edema in the obturator muscles. Blood cultures are negative. Ultrasound-guided aspiration reveals no abscess, but fluid obtained grows methicillin-resistant Staphylococcus aureus (MRSA). In addition to antibiotic treatment, what other treatment option is recommended:

. Surgical irrigation and debridement
. Indwelling catheter drainage
. Repeated aspiration with ultrasound guidance
. Observation
. Spica cast application

Correct Answer & Explanation

. Observation

Explanation

This patient has community-acquired MRSA but does not have an evident fluid collection. There is no evidence of systemic infection or necrotizing fasciitis. There is no indication for drainage or debridement of any type. Therefore, antibiotics alone with clinical observation are indicated.

Question 47

Topic: Infection, Pharmacology & VTE

A 5-year-old girl who presents to the emergency department has obturator muscle infection without abscess formation, which is seen on magnetic resonance imaging. She has no clinical evidence of sepsis. Aspiration yields methicillin-resistant Staphylococcus aureus (MRSA). Which of the following antibiotics is recommended:

. Vancomycin
. C lindamycin
. Rifampin
. Tetracycline
. Linezolid

Correct Answer & Explanation

. C lindamycin

Explanation

To treat this patient, clindamycin is the drug of choice. Vancomycin is not recommended for uncomplicated MRSA in the nonseptic patient. Rifampin is not recommended to be used alone because of the rapid development of resistance. Tetracycline is not recommended for children under 8 years old because it causes permanent staining of the teeth. Linezolid is to be used only after infectious disease consultation because of its toxicity (thrombocytopenia in 3.5% of patients) and expense. Another option for this patient would be trimetoprim/sulfamethoxazole.

Question 48

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with a swollen, erythematous knee. Joint aspiration yields purulent fluid, but standard agar cultures are negative at 48 hours. What is the most appropriate method to identify the most likely atypical causative organism in this age group?
. Fungal cultures
. Acid-fast bacilli smear
. Inoculation of synovial fluid into blood culture vials (BACTEC)
. Synovial biopsy
. Dark-field microscopy

Correct Answer & Explanation

. Inoculation of synovial fluid into blood culture vials (BACTEC)

Explanation

Kingella kingae is a very common cause of septic arthritis in toddlers but is fastidious on solid media. Inoculation of synovial fluid directly into liquid blood culture vials significantly improves the diagnostic yield.

Question 49

Topic: Infection, Pharmacology & VTE

A 7-year-old boy presents with a limp, fever, and inability to bear weight. Hip range of motion is slightly limited at the extremes but relatively painless in the mid-arc. Inflammatory markers are elevated. MRI reveals abnormal marrow signal in the ilium.

What is the most appropriate initial management for uncomplicated acute pelvic osteomyelitis?

. Immediate surgical debridement of the pelvis
. Intravenous antibiotics
. Emergent arthrotomy of the hip joint
. Spica cast immobilization
. CT-guided core biopsy of the bone

Correct Answer & Explanation

. Intravenous antibiotics

Explanation

Acute pelvic osteomyelitis frequently mimics a septic hip but usually preserves functional, painless hip motion in the mid-arc. First-line treatment for uncomplicated cases without a large drainable abscess is intravenous antibiotics.

Question 50

Topic: Infection, Pharmacology & VTE

Methicillin resistance in Staphylococcus aureus (MRSA) is primarily mediated by which of the following molecular mechanisms?

. Upregulation of efflux pumps
. Overproduction of beta-lactamase
. Alteration of penicillin-binding protein 2a (PBP2a)
. Mutation of DNA gyrase
. Decreased outer membrane permeability

Correct Answer & Explanation

. Alteration of penicillin-binding protein 2a (PBP2a)

Explanation

MRSA strains acquire the mecA gene, which encodes for a variant penicillin-binding protein called PBP2a. This altered protein has a severely reduced affinity for beta-lactam antibiotics, rendering them ineffective.

Question 51

Topic: Infection, Pharmacology & VTE

Community-acquired MRSA (CA-MRSA) strains frequently produce a specific toxin that is highly associated with severe deep tissue infections and necrotizing pneumonia. Which toxin is this?

. Toxic shock syndrome toxin-1 (TSST-1)
. Exfoliative toxin A
. Panton-Valentine leukocidin (PVL)
. Alpha-hemolysin
. Enterotoxin B

Correct Answer & Explanation

. Panton-Valentine leukocidin (PVL)

Explanation

Panton-Valentine leukocidin (PVL) is a pore-forming cytotoxin that destroys leukocytes and causes severe tissue necrosis. It is a key virulence factor in many highly aggressive CA-MRSA infections.

Question 52

Topic: Infection, Pharmacology & VTE

A 3-week-old neonate presents with a septic hip. Pending culture results, which of the following empiric intravenous antibiotic regimens is most appropriate?

. Cefazolin alone
. Cefotaxime and Vancomycin
. Clindamycin and Gentamicin
. Amoxicillin and Clavulanate
. Erythromycin and Rifampin

Correct Answer & Explanation

. Cefotaxime and Vancomycin

Explanation

Empiric coverage for neonatal septic arthritis must target S. aureus, Group B Streptococcus, and Gram-negative bacilli. A combination of vancomycin (for MRSA) and a 3rd-generation cephalosporin (like cefotaxime) provides the necessary broad-spectrum coverage.

Question 53

Topic: Infection, Pharmacology & VTE

A 6-year-old child with sickle cell disease presents with femoral osteomyelitis. While Staphylococcus aureus is highly prevalent, which organism is uniquely responsible for a disproportionately high percentage of osteomyelitis cases in this specific patient population?

. Staphylococcus aureus
. Salmonella species
. Streptococcus pneumoniae
. Haemophilus influenzae
. Kingella kingae

Correct Answer & Explanation

. Salmonella species

Explanation

Due to hyposplenism and episodic bowel ischemia, patients with sickle hemoglobinopathies are uniquely susceptible to systemic infection and subsequent osteomyelitis caused by Salmonella species.

Question 54

Topic: Infection, Pharmacology & VTE

According to the Kocher criteria, what is the predictive probability of septic arthritis in a child who presents with a fever of 38.6 degrees C, inability to bear weight, ESR of 45 mm/hr, and a serum WBC count of 13,000 cells/mm3?

. Less than 5%
. 10 to 20%
. 40 to 50%
. 93 to 99%
. 100%

Correct Answer & Explanation

. 93 to 99%

Explanation

The patient meets all four Kocher criteria: fever > 38.5 C, non-weight-bearing, ESR > 40, and WBC > 12,000. The presence of all four criteria yields a 93-99% probability of septic arthritis.

Question 55

Topic: Infection, Pharmacology & VTE

A 9-year-old girl presents with recurrent episodes of clavicular and tibial pain. Radiographs show sclerotic and lytic lesions. Multiple bone biopsies have yielded no bacterial growth, and she has not responded to prolonged IV antibiotics. What is the most appropriate next step in management?

. Escalate to broader-spectrum antibiotics
. Initiate a scheduled trial of nonsteroidal anti-inflammatory drugs (NSAIDs)
. Perform a radical surgical debridement
. Start systemic oral corticosteroids
. Refer for low-dose radiation therapy

Correct Answer & Explanation

. Initiate a scheduled trial of nonsteroidal anti-inflammatory drugs (NSAIDs)

Explanation

The clinical presentation is classic for Chronic Recurrent Multifocal Osteomyelitis (CRMO), an autoinflammatory disorder rather than an infection. First-line therapy for CRMO is the scheduled use of NSAIDs.

Question 56

Topic: Infection, Pharmacology & VTE
A 14-year-old boy with a localized MRSA abscess develops sudden onset high fever, hypotension, and a diffuse macular erythroderma. Labs reveal acute kidney injury. This shock syndrome is mediated by which of the following mechanisms?
. Direct bacterial invasion of the myocardium
. Endotoxin release from Gram-negative bacterial cell walls
. Superantigen cross-linking of MHC class II and T-cell receptors
. Type III immune complex hypersensitivity reaction
. Intravascular coagulation induced directly by PVL toxin

Correct Answer & Explanation

. Superantigen cross-linking of MHC class II and T-cell receptors

Explanation

Staphylococcal Toxic Shock Syndrome is caused by superantigens (such as TSST-1). These proteins cross-link MHC class II molecules directly to T-cell receptors, triggering a massive, uncoordinated cytokine storm.

Question 57

Topic: Infection, Pharmacology & VTE

A 5-year-old child is treated for uncomplicated acute hematogenous osteomyelitis of the femur. After a week of intravenous antibiotics, the child is afebrile, and the CRP has normalized. What is the currently recommended total duration of antibiotic therapy (IV plus oral step-down)?

. 10 days
. 3 to 4 weeks
. 6 to 8 weeks
. 12 weeks
. 6 months

Correct Answer & Explanation

. 3 to 4 weeks

Explanation

For uncomplicated acute hematogenous osteomyelitis in children with a rapid clinical and serologic response, a short course (typically 3 to 4 weeks total) of antibiotics is considered safe and effective.

Question 58

Topic: Infection, Pharmacology & VTE

An 8-year-old girl is ready for discharge following surgical drainage of a CA-MRSA soft tissue abscess. She is prescribed an oral step-down antibiotic. Which of the following is an appropriate oral agent for MRSA that does NOT require routine monitoring for myelosuppression?

. Trimethoprim-sulfamethoxazole
. Linezolid
. Tetracycline
. Ciprofloxacin
. Cefdinir

Correct Answer & Explanation

. Trimethoprim-sulfamethoxazole

Explanation

Trimethoprim-sulfamethoxazole (TMP-SMX) is highly effective for CA-MRSA skin and soft tissue infections. Linezolid requires monitoring for myelosuppression (especially for use >2 weeks), and tetracyclines are avoided under age 8 due to tooth discoloration.

Question 59

Topic: Infection, Pharmacology & VTE

Which of the following is NOT one of the classic Kocher criteria used to differentiate septic arthritis of the hip from transient synovitis in children?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate (ESR) > 40 mm/hr
. Temperature > 38.5°C (101.3°F)
. Serum C-reactive protein (CRP) > 2.0 mg/dL
. Serum white blood cell (WBC) count > 12,000 cells/mm3

Correct Answer & Explanation

. Serum C-reactive protein (CRP) > 2.0 mg/dL

Explanation

The classic Kocher criteria include non-weight-bearing, ESR >40, fever >38.5°C, and WBC >12,000. While CRP >2.0 mg/dL was later identified by Caird et al. as an excellent independent predictor, it is not one of the original four Kocher criteria.

Question 60

Topic: Infection, Pharmacology & VTE
A 2-year-old girl presents with a warm, swollen knee and refusal to walk. Aspiration yields purulent synovial fluid, but standard agar cultures remain sterile at 48 hours. What is the optimal method for isolating the most likely causative organism in this age group?
. Prolonged incubation on MacConkey agar for 14 days
. Inoculation of the synovial fluid into aerobic BACTEC blood culture vials
. Acid-fast bacilli (AFB) staining and Lowenstein-Jensen culture
. Viral culture of the synovial fluid
. Direct immunofluorescence assay for Borrelia burgdorferi

Correct Answer & Explanation

. Inoculation of the synovial fluid into aerobic BACTEC blood culture vials

Explanation

Kingella kingae is a fastidious organism and a leading cause of septic arthritis in children aged 6 months to 4 years. Its isolation is significantly improved by inoculating synovial fluid directly into aerobic blood culture vials or by using PCR.

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