In emergency rooms and intensive care units across the country, clinicians make split-second decisions about which antibiotics to give a patient. A new study reveals that these decisions may have unintended consequences for patient outcomes. Beginning in 2015, a 15-month national shortage of a commonly prescribed antibiotic, piperacillin/tazobactam--known by the brand name Zosyn--provided a unique opportunity to compare rates of death in hospitalized patients with sepsis who were administered two different types of antibiotics—one that spares the gut microbiome and one that profoundly alters it. Piperacillin/tazobactam is a broad-spectrum antibiotic that is commonly administered for sepsis, a life-threatening complication from...