A 17-year-old athlete presents with itchy, circular, scaly lesions on his feet. KOH preparation of skin scrapings shows branching septate hyphae. Which of the following best describes the nutritional requirement and tissue tropism of this organism?

A 60-year-old man develops postoperative wound infection. Gram-positive cocci in clusters are isolated and found resistant to oxacillin and cefoxitin. Which gene product mediates this resistance?

A 25-year-old intravenous drug user develops fever, hypotension, and diffuse erythematous rash that desquamates a few days later. Blood cultures grow Gram-positive cocci in clusters. Which of the following best describes the mechanism by which the responsible exotoxin causes this patient’s symptoms?

A 55-year-old man presents with fever, productive cough, and chest X-ray suggesting lobar pneumonia. Culture on blood agar shows α-hemolytic colonies. The organism is bile soluble and optochin sensitive. Which of the following is the most likely causative organism?

A 25-year-old woman with pelvic pain and purulent cervical discharge has Gram-negative diplococci inside neutrophils. Which culture media is most appropriate to isolate the causative organism?

A 70-year-old woman develops watery diarrhea after 10 days of clindamycin therapy. Stool culture grows no pathogens on routine media. Which of the following tests is most useful for confirming the diagnosis?

A 45-year-old diabetic woman has white plaques on her oral mucosa that scrape off easily. A KOH prep shows budding yeast. Which of the following in-vitro tests helps confirm the identity of the organism?

A 32-year-old man with jaundice has serologic test showing positive HBsAg and anti-HBc IgM. Which of the following best describes his infection status?

Gram-positive cocci in clusters are isolated from pus. The organism is catalase positive, coagulase positive, and resistant to many β-lactam antibiotics. Which of the following phenotypic methods is recommended by CLSI for confirming MRSA?

A 23-year-old man presents with fever, abdominal pain, and diarrhea after eating undercooked chicken. Stool culture shows non-lactose fermenting colonies on MacConkey agar, H2S production on TSI slant, and motile Gram-negative rods. Which of the following organisms is most likely responsible?

A 35-year-old man presents with a chronic draining jaw abscess following a dental extraction. The pus is thick and contains yellow granules (“sulfur granules”). Gram stain shows branching Gram-positive rods. The organism is anaerobic and non–acid-fast. Which of the following is the most likely etiologic agent?

A 27-year-old man presents with a painful, fluctuant abscess on his thigh. Gram stain from pus shows Gram-positive cocci in clusters. The isolate grows on blood agar, is coagulase positive, and resistant to oxacillin and cefoxitin. Which of the following is the most appropriate therapy?

A 65-year-old ventilated patient develops fever and purulent sputum. Gram-negative rods producing blue-green pigment and a grape-like odor grow on culture. Which of the following has the best coverage for this bacteria?

A 42-year-old HIV-positive man presents with headache, fever, and neck stiffness. India ink preparation of CSF shows encapsulated yeast with clear halos. Which of the following is the most appropriate initial therapy?

A neutropenic patient develops hemoptysis and pulmonary nodules with a halo sign on CT. Sputum shows acute-angle branching septate hyphae. Which antifungal is preferred?

A 10-year-old boy is bitten by a stray dog. The wound is cleaned, and the dog cannot be found. What is the next best step?

A 30-year-old woman presents with fever, myalgia, and dry cough for 1 day. Rapid antigen test is positive for influenza A. Which antiviral is most appropriate?

A 45-year-old man with chronic hepatitis B has elevated ALT and high HBV DNA level. Serology: HBsAg (+), HBeAg (+). Which of the following is the most appropriate long-term therapy?

A college student presents with meningococcemia and dies shortly after admission. Which of the following measures should be taken for close contacts?

A 70-year-old woman with dementia develops fever. She has an indwelling Foley catheter for 10 days. Urine culture grows E. coli ≥ $$10^5$$ CFU/mL. Which intervention most effectively reduces risk of CAUTI in hospitalized patients?

A 56-year-old ICU patient develops sepsis 6 days after central venous catheter insertion. What is the best preventive strategy to reduce CLABSI incidence?

A patient on mechanical ventilation for 8 days develops pneumonia. Which following measure is effective for reducing VAP?

A 45-year-old woman undergoes colon surgery. To prevent surgical site infection, which practice is most appropriate?

A patient on broad-spectrum antibiotics develops diarrhea; stool PCR is positive for Clostridioides difficile. What infection control measure is most essential?

During an influenza pandemic, hospitals in the city are overwhelmed. Which public health intervention is most effective to reduce transmission in the community?

A traveler returning from a region with Ebola outbreak. He is asymptomatic but has high-risk contact history. Which measure is most appropriate?

During a COVID-19 vaccine rollout, supply is limited. According to WHO guidance, which group should be prioritized?