Clinical Microbiology: Infectious Disease Cases & Treatments

A gram stain from a patient with urosepsis shows pink rods. Which cell wall feature of this organism triggers the strong immune response that can lead to sepsis?

An outer membrane with LPS

A 62-year-old man has a chronic cough, night sweats and weight loss. A gram stain of his sputum shows no organisms. Which stain should be ordered next?

Acid-fast stain

Which of the following is a treatment for mycobacterial infections?

Ethambutol

An immunocompromised patient is suspected of having an invasive fungal infection, but the organism is unknown. Which test looks for a fungal cell wall component and detects a broad range of fungi?

Beta-D-glucan assay

Which test is considered the gold standard because it identifies the organism AND its antibiotic susceptibility?

Culture

In which patient should you NOT delay antibiotics while waiting for culture results?

A 19-year-old with fever, a stiff neck and suspected bacterial meningitis

A hospitalized patient has normal formed stools and no abdominal symptoms. Her roommate was just diagnosed with C. diff, and the family asks for her to be tested. What is the best response?

Do not test; only test patients with symptoms

A 30-year-old competitive swimmer has an ear infection. The culture grows gram-negative rods with a greenish pigment and a metallic sheen. What is the organism?

Pseudomonas aeruginosa

A ventilated ICU patient develops pneumonia. The sputum culture grows Staph aureus, and the PCR is positive for the mecA gene. What is the best treatment?

IV vancomycin

A 14-year-old with no drug allergies has a fever, tonsillar exudates, tender anterior neck nodes and no cough. His rapid antigen test is positive. What is the first-line treatment?

Penicillin/amoxicillin PO

Which finding best distinguishes an UPPER urinary tract infection from a LOWER one?

Fever with flank pain

A 29-year-old woman has a fever of 101.5°F, flank pain and nausea, and she will be treated as an outpatient. Which choice is NOT appropriate?

Nitrofurantoin (Macrobid)

A 26-year-old man has a painless ulcer with a rolled border on his penis, 3 weeks after a new sexual partner. His inguinal lymph nodes are enlarged but not tender. What is the treatment?

Penicillin G

After a patient is treated for syphilis, how do you know the treatment worked?

Follow RPR/VDRL titers for a 4-fold decline

A hiker has an expanding target-shaped rash 5 days after a tick bite in Maine. His Lyme antibody test comes back negative. What is the most likely explanation?

Antibodies haven't formed yet (window period)

A deer tick was attached to a patient for about 2 days and was removed this morning, in a Lyme-endemic area. The patient has no symptoms. What is the best management?

Doxycycline 200 mg once

A 21-year-old man has a purulent urethral discharge. PCR is positive for Neisseria gonorrhoeae, and his chlamydia results are not available. What is the best treatment?

IM ceftriaxone, and also treat for chlamydia (doxycycline)

A 31-year-old has a genital lesion that started as a red bump, became a pustule within 2 days and is now a very painful ulcer. He also has large, painful swollen groin lymph nodes. What is the organism?

Haemophilus ducreyi

Which feature best distinguishes encephalitis from meningitis?

Altered brain function (confusion, personality change, speech difficulty)

A CSF analysis shows clear fluid, lymphocytes, mildly raised protein and normal glucose. What is the most likely diagnosis?

Viral meningitis

A 68-year-old on chemotherapy has fever, a stiff neck and photophobia. You suspect bacterial meningitis. What is the best empiric treatment?

IV ceftriaxone + IV vancomycin + IV ampicillin

A patient with advanced HIV has had headache, fever and confusion for 2 weeks. The CSF cryptococcal antigen is positive. What is the initial treatment?

IV amphotericin B +/- flucytosine

A patient with HIV and a CD4 count of 90 has 3 weeks of progressive dyspnea and a dry cough. His O2 sat is 86%, a CT shows ground glass opacities and his LDH is elevated. What is the treatment?

TMP/SMX (Bactrim) x21 days + steroids

A patient is diagnosed with invasive aspergillosis. Which antifungal is the first line?

Voriconazole

Which patient needs anaerobic coverage?

A man with an intra-abdominal abscess after a bowel perforation

A healthy 23-year-old woman has uncomplicated cystitis. What is the most likely organism?

E. coli

Giving doxycycline 200 mg once after a tick bite is an example of:

Prophylaxis