Researchers who surveyed microbial community composition on various surfaces and people inside a newly-opened hospital as the facility became operational now report important insights into how humans and unseen life influence one another within constructed environments. Every individual plays host to billions of bacteria living on their skin and inside their bodies, a dynamic community referred to as the microbiota, which also inhabits most of the seemingly-lifeless objects in people's surroundings. While bacteria acquired during a hospital stay may influence patient outcomes, no studies have characterized how the microbiota of a health care facility is established and evolves over time. Simon Lax and colleagues took samples from the Center for Care and Discovery at the University of Chicago for a two month period prior to opening and subsequently for a full year after the hospital was up and running. They collected 6,523 microbial samples from multiple sites in 10 patient care rooms and two nurse stations split across two hospital floors - swabbing participant's hands, noses, armpits, and personal cell phones to follow how microbes transferred between individuals and the environment. The researchers observed that patients initially acquired bacteria present in the room before their stay, yet subsequently their own microbial signatures began to influence what was already on the surrounding walls. Lax et al. also parsed out changes in microbial diversity associated with clinical factors (such as patient ambulatory status, antibiotic use, and treatment with chemotherapy) and environmental conditions (including room humidity and temperature). The authors say the findings may provide much needed context for future studies of hospital-acquired infections, which remain a leading cause of patient death.