Doctors prescribed antibiotics to children with respiratory tract infections at nearly twice the expected rate, researchers from the University of Washington Schools of Medicine and Public Health and Seattle Children's Research Institute have found. That amounts to more than 11 million unnecessary antibiotic prescriptions a year.

The study, published recently in Pediatrics, was an analysis of studies conducted between 2000 and 2011. The researchers estimated that 27 percent of children under 18 with ear, nose, throat and upper respiratory tract infections had illnesses caused by bacteria. Antibiotic prescriptions were given to nearly 57 percent of them, the researchers said.

Antibiotics, or antibacterial agents, do not fight infections caused by viruses like colds or flu. Over time, bacteria can build up resistance to antibiotics, "posing both individual and community risks," the researchers noted. One challenge for doctors is the lack of tools to distinguish quickly between viral and bacterial infections.

The study was co-authored by University of Washington School of Public Health faculty Rita Mangione-Smith, adjunct professor of Health Services (also professor of Pediatrics), and Chuan Zhou, adjunct research associate professor of Health Services (also research associate professor of Pediatrics). First author was Matthew Kronman, assistant professor of Pediatrics at the University of Washington. All three are on faculty at Seattle Children's.