ESBL Pyelonephritis with Penicillin Anaphylaxis
Mr. D, 58, with type 2 diabetes, presents with 2 days of fever (39.1°C), right flank pain, and dysuria. BP 102/66 mmHg, HR 112/min. Urine culture grows >100,000 CFU/mL Escherichia coli. Susceptibilities: ampicillin R, ampicillin-sulbactam R, piperacillin-tazobactam R, ceftriaxone R, cefepime R, meropenem S, ertapenem S, gentamicin S, amikacin S, ciprofloxacin R, levofloxacin R, trimethoprim-sulfamethoxazole R, nitrofurantoin S. The patient reports a penicillin allergy with hives and throat swelling 10 years ago. Blood cultures are negative at 24 hours. The patient is admitted and started on IV fluids. The pharmacy asks for an antibiotic recommendation. The patient has no history of multidrug-resistant organisms and has not traveled outside the country.
1. Interpret the susceptibility pattern. What resistance mechanism is most likely, and why is nitrofurantoin not appropriate?
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The isolate is an extended-spectrum β-lactamase (ESBL)-producing E. coli. Resistance to ceftriaxone and cefepime along with piperacillin-tazobactam, but susceptibility to meropenem and ertapenem, is the classic pattern; ESBLs hydrolyze penicillins and cephalosporins but not carbapenems. The co-resistance to ciprofloxacin, levofloxacin, and trimethoprim-sulfamethoxazole is common because ESBL plasmids often carry additional resistance genes. Nitrofurantoin is susceptible in vitro, but it concentrates in urine and is not reliable for pyelonephritis with systemic symptoms. The negative blood cultures do not exclude pyelonephritis. The lab should confirm ESBL by a phenotypic test (e.g., combination disk) and report it to guide therapy and infection control.
2. Given the severe penicillin allergy, what antibiotic should be recommended, and what precautions apply?
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Use ertapenem 1 g IV every 24 hours, or meropenem 1 g IV every 8 hours if the patient is unstable or the local ertapenem MIC is high. Carbapenems are the drugs of choice for ESBL pyelonephritis. The history is anaphylaxis to penicillin, but carbapenem cross-reactivity is low (~1% or less), and even lower with ertapenem and meropenem; give the first dose with observation and epinephrine available. Avoid cephalosporins because the organism is resistant and cross-reactivity with penicillin is higher. Avoid nitrofurantoin because it does not treat tissue infection. A carbapenem-sparing option such as gentamicin could be used if a carbapenem is refused, but it carries nephrotoxicity and requires monitoring.
3. What infection-control measures are indicated, and what follow-up cultures are needed?
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Place the patient in contact precautions in a private room, with dedicated equipment and hand hygiene. Flag the chart and notify the receiving units and the microbiology laboratory so that the ESBL status is communicated on transfers. No decolonization is recommended for ESBL E. coli; focus on hand hygiene, environmental cleaning, and antimicrobial stewardship. If the patient has a urinary catheter, remove it as soon as possible. Repeat urine culture only if symptoms persist or recur. Counsel the patient about the resistant organism and the importance of completing therapy.