Infectious Diseases

A 74-year-old woman is evaluated in the outpatient clinic for medical clearance 3 days prior to an elective right total hip arthroplasty. Her medical history includes well-controlled type 2 diabetes mellitus, essential hypertension, and osteoarthritis. She reports feeling well and explicitly denies fever, chills, flank pain, dysuria, or increased urinary frequency. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 128/78 mmHg, and a pulse of 76/min. Physical examination is unremarkable with no costovertebral angle tenderness or suprapubic pain. As part of a preoperative protocol mandated by the surgical center, a urinalysis and urine culture are obtained. The urinalysis reveals a specific gravity of 1.018, pH of 6.5, positive leukocyte esterase, positive nitrites, and 45 white blood cells per high-power field. Two days later, the urine culture grows $>10^5$ CFU/mL of *Klebsiella pneumoniae*. Antimicrobial susceptibility testing indicates the isolate is susceptible to cephalexin, ciprofloxacin, and trimethoprim-sulfamethoxazole. Which of the following is the most appropriate management regarding the patient's urinary findings?

A 32-year-old man comes to the clinic for follow-up of a diarrheal illness. Three days ago, he developed fever, diffuse abdominal cramping, and multiple episodes of watery, non-bloody diarrhea after attending a family picnic. He was seen at an urgent care clinic yesterday where a stool culture was obtained and intravenous fluids were administered. Today, he reports that his fever has resolved and his diarrhea is beginning to improve, though he still has 2 to 3 loose stools per day. He is able to tolerate oral fluids and feels well-hydrated. His temperature is 37.1°C (98.8°F), blood pressure is 122/80 mmHg, and pulse is 76/min. The urgent care clinic forwards his stool culture results, which are positive for non-typhoidal *Salmonella enterica*. Susceptibility testing shows the isolate is pan-susceptible. Which of the following is the most appropriate antimicrobial management?

A 62-year-old man with a 15-year history of poorly controlled type 2 diabetes mellitus and peripheral neuropathy is evaluated in the clinic for a chronic right foot ulcer. He first noticed the ulcer 6 weeks ago. The patient is afebrile, and his vital signs are strictly within normal limits. On physical examination, there is a $3 \times 3$ cm non-tender ulcer on the plantar surface of the right first metatarsal head. There is no surrounding erythema, warmth, fluctuance, or purulent drainage. A sterile metal probe is introduced into the ulcer and easily palpates a hard, gritty surface at the base. The physician highly suspects underlying osteomyelitis.

Arrange the following diagnostic and therapeutic steps in the most appropriate chronological sequence for the standard medical management of this patient.

A 58-year-old man is brought to the emergency department by his wife due to fever, severe headache, and confusion that started 12 hours ago. His wife reports that he has also been dragging his right leg since the onset of symptoms. His temperature is 39.2°C (102.6°F), blood pressure is 145/90 mm Hg, and pulse is 110/min. Physical examination reveals marked nuchal rigidity and right-sided hemiparesis. He is lethargic but arouses to verbal stimuli. Arrange the following management steps in the most appropriate chronological order.

A 68-year-old man is evaluated in the intensive care unit on his fifth day of mechanical ventilation. He originally presented with severe acute pancreatitis complicated by acute respiratory distress syndrome. Three days ago, he developed a temperature of $39.2^\circ\text{C}$ ($102.6^\circ\text{F}$), increased purulent endotracheal secretions, and a new right lower lobe infiltrate on chest radiograph. He was diagnosed with ventilator-associated pneumonia and empirically started on intravenous vancomycin, cefepime, and tobramycin. Today, his temperature is $37.4^\circ\text{C}$ ($99.3^\circ\text{F}$), and his oxygen requirements have decreased. The endotracheal aspirate culture from three days ago grows heavy growth ($>10^5\text{ CFU/mL}$) of *Klebsiella pneumoniae*. Susceptibility testing reveals resistance to ampicillin, but susceptibility to ceftriaxone, cefepime, piperacillin-tazobactam, and meropenem. Blood cultures are negative. Which of the following is the most appropriate next step in this patient's antimicrobial management?

A 71-year-old man is evaluated on the medical ward on hospital day 3. He was initially admitted for severe community-acquired pneumonia presenting with fever, productive cough, hypoxemia, and a dense left lower lobe consolidation on a chest radiograph. At the time of admission, empiric therapy with intravenous ceftriaxone and oral azithromycin was initiated. He has shown excellent clinical improvement; his oxygen requirements have resolved, and he has been afebrile for the past 24 hours. The patient is currently tolerating a regular diet and ambulating in the hallways. Both blood and high-quality sputum cultures obtained on admission have finalized, demonstrating the growth of *Streptococcus pneumoniae*. Susceptibility testing results for the isolate are as follows:

The patient is being prepared for discharge with a prescription to complete a 7-day total course of antibiotics. Which of the following is the most appropriate antibiotic regimen for this patient's discharge?

A patient receiving cytotoxic chemotherapy for acute myeloid leukemia arrives at the oncology triage unit reporting severe chills and a recorded temperature of $38.8^\circ\text{C}$ ($101.8^\circ\text{F}$). Her blood pressure is $100/60\text{ mm Hg}$, and her heart rate is $112/\text{min}$. She has an indwelling totally implantable venous access device. Laboratory analysis reveals an absolute neutrophil count of $350/\text{mm}^3$.

Arrange the following interventions in the most appropriate sequential order for managing this patient's condition according to standard clinical guidelines for high-risk febrile neutropenia.

A 25-year-old medical student is reviewing post-exposure prophylaxis protocols for various infectious disease scenarios. Which prophylactic regimen is most appropriate for each of the following patient exposures?

During bedside rounds on the medical ward, the care team evaluates a 28-year-old woman who is currently on her third day of hospitalization for acute pyelonephritis. At the time of admission, she reported right-sided flank pain, nausea, and subjective fevers, prompting the initiation of empiric intravenous ceftriaxone. Her symptoms have now completely resolved, and she has been tolerating a regular diet since yesterday evening. Vital signs are temperature 37.1°C (98.8°F), blood pressure 118/76 mm Hg, pulse 78/min, and respirations 14/min. The urine culture collected on admission has finalized, demonstrating $> 10^5$ CFU/mL of *Escherichia coli*. Antimicrobial susceptibility testing indicates that the isolate is resistant to ampicillin and ciprofloxacin, but is susceptible to ceftriaxone, trimethoprim-sulfamethoxazole, nitrofurantoin, and meropenem. Which of the following is the most appropriate next step in management?

Correlate the following clinical scenarios involving suspected central nervous system infections with the most appropriate empiric or targeted pharmacotherapy.

A 32-year-old man presents to the emergency department with a 4-week history of productive cough, occasional hemoptysis, low-grade fevers, and night sweats. He has experienced a 5-kg (11-lb) unintentional weight loss during this time. The patient immigrated to the United States from a region highly endemic for tuberculosis two months ago. His temperature is 37.8°C (100.0°F), blood pressure is 120/78 mm Hg, pulse is 88/min, and respiratory rate is 16/min. Physical examination reveals bronchial breath sounds and crackles in the right upper lung field. The clinical presentation is highly suspicious for active pulmonary tuberculosis. Arrange the following management steps in the most appropriate chronological order.

A 29-year-old man is evaluated in the hospital for ongoing fever. He was admitted 4 days ago with high fevers, chills, and pleuritic chest pain. His medical history is significant for opioid use disorder with active intravenous heroin use. On admission, his temperature was 39.2°C (102.6°F). Physical examination revealed a new holosystolic murmur at the lower left sternal border. Computed tomography of the chest showed multiple peripheral cavitary lesions. Two sets of blood cultures were drawn, and he was started on empiric intravenous vancomycin and ceftriaxone. A transthoracic echocardiogram demonstrated a 1.5-cm mobile vegetation on the anterior leaflet of the tricuspid valve. Today, the patient's temperature is 38.4°C (101.1°F). The admission blood cultures are now growing methicillin-susceptible *Staphylococcus aureus* (MSSA). Which of the following is the most appropriate next step in pharmacotherapy?

Select the most appropriate first-line antimicrobial therapy for each of the following patients presenting with a characteristic infectious syndrome.

A 68-year-old man comes to the clinic reporting the onset of frequent, watery, non-bloody diarrhea occurring up to $7$ times daily over the past $3$ days. He also notes mild, diffuse lower abdominal cramping. His medical history is significant for hypertension and hyperlipidemia. Two weeks ago, he completed a 10-day course of oral amoxicillin-clavulanate for acute bacterial sinusitis. His temperature is $38.1^\circ\text{C}$ ($100.6^\circ\text{F}$), blood pressure is $118/76 \text{ mmHg}$, and heart rate is $92/\text{min}$. Physical examination reveals mild diffuse abdominal tenderness with normal bowel sounds; there is no guarding or rebound tenderness. Laboratory testing shows a leukocyte count of $14,500/\text{mm}^3$ and a serum creatinine of $1.1 \text{ mg/dL}$ (baseline $1.0 \text{ mg/dL}$). A stool nucleic acid amplification test is positive for *Clostridioides difficile* toxin genes. Which of the following is the most appropriate next step in management?

A 54-year-old man with a history of poorly controlled HIV (most recent CD4 count 112 cells/mm³) is brought to the emergency department by his partner due to fever, severe headache, and confusion over the past 24 hours. His temperature is 39.1°C (102.4°F), blood pressure is 110/70 mm Hg, pulse is 112/min, and respiratory rate is 18/min. Physical examination reveals nuchal rigidity and a new right-sided pronator drift. The physician suspects acute bacterial meningitis. Arrange the following steps in the most appropriate chronological sequence for the management of this patient.

A primary care physician evaluates a 45-year-old woman who noticed an expanding area of redness on her right shin that began 48 hours ago. The affected region is tender to the touch, and she reports feeling mildly fatigued but denies chills, nausea, or recent trauma. Medical history is notable only for mild allergic rhinitis, for which she takes over-the-counter cetirizine. Her temperature is $37.9^\circ\text{C}$ ($100.2^\circ\text{F}$), blood pressure is $122/78 \text{ mmHg}$, pulse is $84/\text{min}$, and respiratory rate is $14/\text{min}$. Physical examination reveals a $10 \times 6 \text{ cm}$ erythematous, warm, and swollen plaque on the anterior right lower leg. The margins are indistinct. There is no palpable fluctuance, purulent exudate, or ulceration. Tender right inguinal lymphadenopathy is present. Which of the following is the most appropriate initial pharmacotherapy for this patient?

A 55-year-old man with a history of intravenous drug use comes to the emergency department reporting severe, unrelenting lower back pain for the past 3 weeks. The pain is worse at night, is not relieved by rest, and is accompanied by subjective fevers. He reports no leg weakness, numbness, or bowel and bladder incontinence. Temperature is 38.2°C (100.8°F), pulse is 92/min, and blood pressure is 128/78 mm Hg. Physical examination shows focal tenderness to percussion over the L4 and L5 spinous processes. Neurologic examination of the lower extremities reveals full strength, normal sensation, and intact reflexes bilaterally. Arrange the following steps in the most appropriate chronological sequence for the diagnostic workup and management of this patient.

A $41$-year-old man is evaluated in the hospital on the third day of his admission for community-acquired pneumonia. He initially presented with a two-day history of high fever, productive cough, and right-sided pleuritic chest pain. On admission, his temperature was $38.8^\circ\text{C}$ ($101.8^\circ\text{F}$), blood pressure was $118/74\text{ mm Hg}$, pulse was $110\text{/min}$, and respirations were $24\text{/min}$. Chest radiography showed a right lower lobe consolidation. He was subsequently started on empiric intravenous levofloxacin.

Today, the patient reports feeling significantly better. He has been afebrile for the past $24\text{ hours}$, and his cough has improved. Current vital signs are temperature $37.1^\circ\text{C}$ ($98.8^\circ\text{F}$), blood pressure $122/78\text{ mm Hg}$, pulse $82\text{/min}$, and respirations $16\text{/min}$. He is tolerating a regular diet.

Blood cultures drawn on admission are now positive for Streptococcus pneumoniae. Susceptibility testing of the isolate demonstrates the following:

Which of the following is the most appropriate next step in pharmacotherapy?

A 28-year-old medical resident sustains a deep percutaneous needle-stick injury to her hand while drawing blood from a patient in the emergency department. The source patient has a documented history of poorly controlled HIV with a high viral load. The hollow-bore needle was visibly contaminated with blood. What is the most appropriate chronological sequence of interventions for this occupational exposure?

An $82$-year-old woman is evaluated in the outpatient clinic for a routine follow-up. She is accompanied by her son, who assists with her activities of daily living. Her medical history is significant for type 2 diabetes mellitus, essential hypertension, and mild neurocognitive disorder. During the visit, the son expresses concern because he has noticed that the patient's urine in her bedside commode has appeared cloudy and distinctly malodorous over the last $72$ hours. He is worried she may have a urinary tract infection, as she was treated for one six months ago. Upon direct questioning, the patient is pleasant and conversant, remaining at her cognitive baseline. She explicitly denies experiencing any dysuria, increased urinary frequency, urinary urgency, flank pain, or subjective fevers. Her vital signs include a temperature of $37.1^{\circ}$ C ($98.8^{\circ}$ F), blood pressure of $135/85$ mmHg, heart rate of $78$/min, and respiratory rate of $14$/min. Abdominal examination is soft and non-tender, with no suprapubic discomfort or costovertebral angle tenderness. A clean-catch urinalysis obtained in the clinic reveals positive leukocyte esterase, positive nitrites, and $35$ white blood cells per high-power field. Which of the following is the most appropriate next step in management?