Infectious Diseases
Core concepts
Sepsis is infection plus organ dysfunction. Obtain cultures, measure lactate, give broad-spectrum antibiotics within an hour, and resuscitate with crystalloid. Necrotizing fasciitis is a surgical emergency with pain out of proportion, bullae, crepitus, and rapid spread; antibiotics alone fail.
Meningitis: start empiric vancomycin plus ceftriaxone immediately, adding ampicillin for patients older than 50 or immunocompromised; dexamethasone before or with the first antibiotic dose reduces hearing loss in pneumococcal disease.
Endocarditis: draw three sets of blood cultures before antibiotics and obtain echocardiography; Staphylococcus aureus bacteremia warrants careful evaluation for endocarditis.
Tuberculosis: latent infection is treated with rifampin-based regimens, active disease requires airborne isolation and multidrug therapy with rifampin, isoniazid, pyrazinamide, and ethambutol.
Human immunodeficiency virus: prophylaxis thresholds are high yield. CD4 below 200 warrants trimethoprim-sulfamethoxazole for Pneumocystis pneumonia, below 100 warrants toxoplasmosis prophylaxis, and below 50 warrants azithromycin for Mycobacterium avium complex.
Clostridioides difficile is treated with oral vancomycin or fidaxomicin; intravenous vancomycin does not treat it, and antiperistaltic agents worsen outcomes. Sexually transmitted infections: treat gonorrhea with ceftriaxone and chlamydia with doxycycline, and treat both when either is found.
Traps
- Delaying antibiotics to obtain imaging in suspected sepsis.
- Using intravenous vancomycin for Clostridioides difficile colitis.
- Missing the need for airborne isolation in active pulmonary tuberculosis.
- Forgetting to cover anaerobes in aspiration pneumonia or dental sources.
Rule of thumb
In any patient with fever and a new murmur, or with Staphylococcus aureus bacteremia, get three sets of blood cultures before antibiotics and obtain an echocardiogram.