The Plot Thickens Patient History A 69 year old male presented to the emergency department (ED) with fever, altered mental status, and hiccups.
Past medical history Seizures Brain cyst removed 2010 Brain shunt placed 2011 History of kidney stones and recurrent urinary tract infections
Empiric treatment started - vancomycin, cefepime, and metronidazole.
Patient’s condition continued to decline. Cefepime was changed to ceftriaxone for possible pneumonia; patient continued on vancomycin.
Blood cultures were drawn.
QUESTIONS: Why are blood cultures (BCx) obtained? How is antimicrobial susceptibility determined?
Patient’s microbiology workup Day 1: Urine and respiratory cultures: Negative Blood cultures: 2 sets positive Gram-positive cocci in clusters MRSA susceptible to vancomycin MIC = 2 µg/ml Day 3: Blood Culture: 2 sets positive again with MRSA; vancomycin MIC = 2 µg/ml Day 6: Blood Culture: 1 set positive with MRSA; vancomycin MIC increased to 4 µg/ml (interpreted as “intermediate” and this MRSA is a VISA!)
Medical technologist recognized the importance of detecting vancomycin-intermediate Staphylococcus aureus (VISA) (MIC 4-8 µg/ml) and called the physician and infection control
Overview of Vancomycin Glycopeptide first released in 1958 Drug of choice for severe infections caused by MRSA Most MRSA do not develop vancomycin resistance even when serially passaged on media containing vancomycin Vancomycin-resistant Staphylococcus aureus (VRSA; (MIC >8 µg/ml) are very uncommon First VRSA case was reported in US in 2002 Only 16 VRSA cases reported worldwide to date
Definitions: VSSA, VISA, VRSA Detection of VISA Tell-tale Signs of VISA From the Bench VISA is typically isolated from patients who have been on extended vancomycin therapy (weeks) The vancomycin MIC of this patient’s initial MRSA isolate was 2 µg/ml susceptible The vancomycin MIC of the third MRSA was 4 µg/ml (VISA) It is likely selective pressure from vancomycin therapy contributed to emergence of VISA Treatment Options for VISA Rifampin + fusidic acid: Combination therapy (not FDA-approved for use in US).
Linezolid (Oxazolidinones): resistance is uncommon