Infectious Disease Clinical Pearls for Hospitalists

Inpatient management of patients with increasingly virulent community acquired and nosocomial infections, ranging from bacteremia to C. difficile colitis, presents hospitalists with challenging choices. The Cleveland Clinic’s Carlos Isada, MD, provided guidance for clinicians at the Society for Hospital Medicine’s 2013 annual conference, held May 17-19 at the National Harbor’s Gaylord Nelson Convention Center in Ft. Washington, MD.

First, Isada addressed the question of whether all patients with Staphylococcus aureus bacteremia (SAB) should receive a transesophageal echocardiogram (TEE). S. aureus is the second leading cause of nosocomial bacteremia after coagulase negative staphylococci, and can be associated with deep-seated infections and a high rate of metastatic infection. Additionally, S. aureus endocarditis can occur even on normal heart valves, with mortality of greater than 35%.

TEEs in patients with SAB confer greater sensitivity and specificity than a trans-thoracic echocardiogram. Procedural complications are rare, though potentially serious. Other cons include expense and possible increased length of stay. The IDSA recommends TEE in adults with methicillin resistant Staphylococcus aureus (MRSA) bacteremia (level A-II). Practice guidelines are evolving; most recommend TEE in all community acquired SAB and for a subset of nosocomial SAB patients.

Next, Isada addressed antibiotic choice for SAB. For methicillin sensitive S. aureus (MSSA), beta lactams are still preferred. Vancomycin is reserved for the penicillin-allergic patient, since it is inferior to oxacillin for MSSA bacteremia. For MRSA bacteremia, choose IV vancomycin or daptomycin (dosed at 6 mg/kg/d or more). Other antibiotics are not approved for SAB and should be considered only for salvage.

When deciding whether to administer a cephalosporin in the context of a penicillin (PCN) allergy, the first step is to determine whether a true allergy exists: 10% of hospitalized patients give a history of PCN allergy, but 90% of these will actually tolerate PCN. True IgE-mediated anaphylaxis occurs in only one to two per 10,000 PCN treatment courses, and most reactions diminish significantly over time. A careful history will help differentiate Type 1 anaphylactic reactions from less serious reactions or non-allergic reactions. PCN skin tests may be used; a variety of algorithms are available to guide testing and treatment. Cross-reactivity of 2-5% with cephalosporins may occur; desensitization is an option, though it carries risks.

Treatment of C. difficile colitis, which is becoming increasingly fulminant with emerging hypervirulent strains, is further complicated when the patient cannot tolerate PO intake. Metronidazole achieves relatively low levels in stool whether administered IV or PO, and IV vancomycin is ineffective. Vancomycin enemas have been used as adjunctive treatment for C. difficile colitis patients with ileus and toxic megacolon, and may be used as part of a triple therapy regime along with oral vancomycin and IV metronidazole. Subtotal colectomy may be considered for severely ill patients.

Finally, Isada examined the utility of plain films versus MRI for diabetic foot infections. Plain films, inexpensive and easily obtained, can reveal soft tissue gas and some foreign bodies. Cortical changes visible on plain films can lag weeks behind actual infection, and sensitivity and specificity are low at 0.54 and 0.68 respectively. MRI, with higher pooled sensitivity of 0.90 and specificity of 0.79-0.83, is also better for diagnosing sinus tracts, abscesses, and soft tissue necrosis. Expense and availability are issues, and an MRI should not supersede a plain film as the first line of imaging in most patients, unless surgical resection or significant abscess are considerations.