This patient should be treated empirically with a carbapenem, such as meropenem, for a possible infection with a multidrug-resistant organism (MDRO). She is at high risk for ventilator-associated pneumonia (VAP) with multidrug-resistant Klebsiella pneumoniae as suggested by gram-negative rods on sputum Gram stain and the presence of other patients in the same ward with extended-spectrum β-lactamase (ESBL)–producing K. pneumoniae infection. ESBLs are enzymes that confer resistance to most β-lactam antibiotics, including penicillins, cephalosporins, and the monobactam aztreonam; they occur only in gram-negative organisms, primarily K. pneumoniae, Klebsiella oxytoca, and Escherichia coli. Carbapenems are less susceptible to ESBLs and provide adequate empiric coverage against this organism, as well as coverage for other possible gram-negative organisms such as Pseudomonas species, which is the second most common cause of VAP following Staphylococcus aureus. With any empiric regimen, antibiotic de-escalation should occur when culture results are available. Meropenem should be changed to ertapenem, a carbapenem without antipseudomonal activity, if an ESBL-producing organism is isolated without Pseudomonas. MDROs are more commonly associated with late-onset (>4 days) VAP. ESBL-producing K. pneumoniae are transmitted by health care personnel using improper hand hygiene or not following contact precautions. Contaminated shared patient care equipment that is not appropriately disinfected between patient uses is another possible route of transmission.

Because extended-spectrum penicillins and cephalosporins share susceptibility to ESBL, cefepime, ceftazidime, and piperacillin-tazobactam would not be optimal empiric therapy in this patient.