As the popularity of electric scooters increases, so do injuries sending users to the hospital, a U.S. study suggests.

Those injured riders are most often young men, without helmets, drunk or stoned, researchers found.

The analysis was done at three southern California trauma centers. The authors found that since introduction of the devices in 2017 as shared rental transportation, injury rates have been climbing. The top injury types were broken bones in the body or the face, followed by bleeding in the head.

Most of the injured were young men, and among those tested for drug or alcohol intoxication, half came back positive, the study team reports in the journal Trauma Surgery and Acute Care Open.

“Anyone who lives in a major city knows the adoption of these new devices is significant,” Dr. Leslie Kobayashi of the University of California, San Diego, said in a phone interview.

To assess the number and nature of injuries related electronic scooters, also called eScooters, Kobayashi and colleagues looked at data on 103 patients admitted San Diego area hospitals with injuries related to eScooter use from September 2017 through October 2018.

The research team found that monthly admissions increased over time, peaking at 43 patients seen in October 2018. Most patients were men between ages 20 and 40, with an average age of 37. About 98% hadn’t been wearing a helmet.

About four in five patients were tested for blood alcohol levels, and nearly half of these patients were found to be intoxicated. Of the 60% given a urine toxicology test, just over half were found to have drugs in their system, most commonly THC, methamphetamine and other amphetamines.

The most common injuries were fractures in legs, ankles or forearms, followed by facial fractures, intracranial hemorrhages and concussions. About a third of patients required surgery. The average hospital stay was three days. Eight patients required ICU admission, and six patients were transferred to long-term acute care. No patients died.

“We were surprised by the number of patients who were intoxicated with alcohol or illicit mind-altering substances,” she said. “After a night out isn’t the best time” to use these devices, she added.

A limitation of the study is that the data came from Level I trauma centers, meaning they reflect the most severe injuries. A follow-up study is looking at emergency department and urgent care cases around San Diego that don’t lead to hospitalization, such as lacerations or fractures that can be fixed quickly, Kobayashi noted. Her teams is also planning a broader study to observe trends around the country.

“If you look at the trend toward an increasing number of injuries through October 2018 and map it out toward today, we’re seeing more and more injuries. It’s a real-time issue we’re trying to get a handle on,” said Dr. Kate Douglass, director of the George Washington University Center for Injury Prevention and Control in Washington, D.C., who wasn’t involved in the study.

Local factors in different cities, such as high-traffic areas and new motorized device regulations, lead to different trends in injuries, Douglass said. Some areas allow people to ride them on the sidewalk, but others require users to ride scooters on the street. Different limitations around when, where and how the scooters can be used, also affect what types of injuries occur.

It’s important for users to know how to ride the devices before taking them on public roads, Douglass added.

“We often see people who hit potholes or curbs and end up fracturing their arm or elbow because they fall,” she said in a phone interview. “Use a safety check and practice your brakes and turns. Make sure you know how to use it before you operate it.”