In the first week of climbing season on Everest, more than 160 climbers have been evacuated or treated for altitude sickness. That’s a remarkably high rate so early in the season, officials say.

Doctors and officials in the region say that 15 patients, including 11 foreign climbers, were evacuated to Kathmandu, and more than 150 overall have been treated, the Himalayan Times reported. They attribute the spike in altitude sickness to inclement weather.

“Most of the patients complained of altitude sickness, as adverse weather has taken a toll on climbing activities this spring season,” Govind Bashyal, an official at a Feriche-based health center, told the Himalayan Times.

One climber with severe gastrointestinal bleeding was evacuated. Others complained of high altitude pulmonary edema and cerebral edema—swelling caused by excess fluid in tissues. A medical camp set up at Base Camp has received 15 patients in two days, Lakpa Sherpa told the Himalayan Times.