A 4-year-old, previously healthy boy is brought to the emergency department due to fever, abdominal pain, and frequent bloody diarrhea for 2 days.  A few children at day care have developed diarrhea over the past week as well.  He takes no medications and has not traveled outside the United States.  Temperature is 39 C (102.2 F), blood pressure is 110/70 mm Hg, and pulse is 90/min.  Physical examination shows increased bowel sounds and left sided abdominal tenderness.  Which of the following is the most likely causal organism?

A 26-year-old man comes to the office due to a progressive rash on his right thigh over the past 4 days.  The patient first noticed a red papule on his leg that grew larger and became tender and ulcerated.  He now also has a painful “knot” in his right groin.  Temperature is 37.8 C (100 F), blood pressure is 110/70 mm Hg, pulse is 88/min, and respirations are 16/min.  A 4-cm, shallow ulceration on the medial right thigh is crusting over and surrounded by erythema.  A prominent 3-cm, fluctuant lymph node is palpated in the right inguinal chain.  Gram stain of a lymph node aspirate sample shows numerous small, gram-negative coccobacilli that stain poorly, findings concerning for Francisella tularensis.  Which of the following risk factors is most consistent with this patient’s diagnosis?

A 64-year-old man comes to the office due to 3 days of diarrhea.  He began to have nausea, vomiting, abdominal cramps, and diarrhea 24 hours after eating chicken salad at a fast-food restaurant.  The patient has had 4-6 episodes of diarrhea per day with no blood in the stool.  He has no tenesmus.  His wife, who ate the same food, had a few loose stools but felt well afterward.  The patient takes a tumor necrosis factor inhibitor for psoriatic arthritis and a proton pump inhibitor for gastritis.  Temperature is 38 C (100 F), blood pressure is 120/70 mm Hg, and pulse is 88/min.  Abdominal examination reveals mild diffuse tenderness to palpation and increased bowel sounds.  Cultures of the stool yield gram-negative bacilli that are nonlactose fermenting and oxidase negative.  Which of the following is the most likely complication associated with this patient’s current infection?

A 32-year-old woman comes to the emergency department due to a mass under her right arm.  She first noticed the mass 3 days ago and it has become progressively more swollen and painful.  The patient has also had 5 days of high fever, chills, generalized muscle aches, and severe fatigue.  She works for the city sanitation department and mentions there has been a recent surge in the rat population due to reduced frequency of trash removal.  Temperature is 38.9 C (102 F), blood pressure is 110/70 mm Hg, pulse is 98/min, and respirations are 14/min.  Physical examination reveals an enlarged, tender right axillary lymph node that is spontaneously draining purulent fluid.  Several lymph nodes in the cervical, axillary, and inguinal regions are enlarged bilaterally.  There are no other wounds or rashes.  Blood cultures and an aspirate from a swollen axillary lymph node grow gram-negative bacilli.  First-line treatment for this patient’s infection most likely involves a drug with which of the following mechanisms of action?

A 20-year-old woman comes to the office with a one-week history of painful swelling in her right axilla that was preceded by malaise, headaches, and night sweats.  Temperature is 37.8 C (100 F), blood pressure is 126/78 mm Hg, and pulse is 88/min.  Physical examination shows enlarged and tender epitrochlear and axillary lymph nodes on the right side.  Histopathologic examination of a lymph node shows scattered necrotizing granulomas and stellate microabscesses containing pleomorphic, gram-negative coccobacilli.  Which of the following is the most likely route of transmission of this patient’s infection?

A 30-year-old man is brought to the emergency department due to high fever, chills, and rigors for 4 hours.  He has no other symptoms.  He was recently diagnosed with Hodgkin lymphoma and received his first cycle of chemotherapy 10 days ago.  Temperature is 39.2 C (102.6 F), blood pressure is 90/40 mm Hg, pulse is 125/min, and respirations are 22/min.  There is no evidence of skin rash or mucositis.  The chest is clear to auscultation.  The abdomen is soft and nontender.  Perianal area is normal.  Laboratory results are as follows:

Chest radiograph is normal.  Urinalysis is normal.  Which of the following is the most likely cause of this patient’s current condition?

A 19-year-old man comes to the emergency department due to dysuria and scrotal pain.  The patient first noticed discomfort with urination and a watery urethral discharge 3 days ago.  Yesterday, he developed pain on the left side of the scrotum while sitting in class.  Vital signs are normal.  On examination, tender swelling is present along the posterior aspect of the left testis, which is otherwise normal in size and position.  Diagnostic testing reveals Chlamydia trachomatis as the sole causative pathogen.  Which of the following additional results are most consistent with this patient’s diagnosis?

A 35-year-old woman comes to the emergency department due to an itchy rash that appeared earlier this morning.  She recently returned from a family vacation at a resort in Cancun.  Two days ago, the patient’s husband developed similar symptoms.  The patient has no significant past medical history and takes no medications.  She has no known allergies.  Her temperature is 37.6 C (99.7 F).  On examination, there is a diffuse, pruritic, papulopustular rash that is most noticeable on the trunk and extremities.  Microbiologic analysis of a pustular fluid sample demonstrates oxidase-positive gram-negative rods that produce pigment on culture medium.  Which of the following is the most likely source of this patient’s infection?