Nearly 500 troops suffered from chilblains, frostbite, hypothermia and trench foot during the most recently studied annual period, more than in any of the previous three years and a 20 percent increase over the previous year.
The reasons for the jump in preventable injuries during what was a mild winter remain unclear, according to a study this month in the Defense Health Agency's Medical Surveillance Monthly Report. The studied covered injuries between July 2017 and July this year.
"Policies and procedures are in place to protect service members against cold weather injuries. Modern cold weather uniforms and equipment provide excellent protection against the cold when used correctly," the study noted. "However, in spite of these safeguards, a significant number of individuals within all military services continue to be affected by cold weather injuries each year."
Fort Wainwright, Alaska, had the highest number of cold injuries diagnosed, with 155 reported cases over five years. Second was the combined Vilseck and Grafenwoehr area in Bavaria, Germany, with 117 cases.
"It's an interesting question why. It's definitely not as cold here," said Maj. Luke Mease, a preventive medicine doctor at U.S. Army Medical Department Activity-Bavaria.
But temperature is just one of several factors, he said, including exposure time.
"Cold weather injuries usually occur when it's cold and wet," Mease said, and Bavarian winters are both cold and damp.
He said that chilblains, a nonfreezing but painful inflammation of small blood vessels in the skin that can cause itching, swelling and blistering, was the most common cold-weather injury in Bavaria.
"These cold injury cases tend to come in clusters," he said. "If we have high-volume, high-activity training events, we'll see more cases."
Usually, he said, affected troops have been in the field overnight or longer. Most often they're young and junior in rank.
"These may be the soldiers that are least likely to speak up," Mease said. "I think it highlights the importance for commanders and line leaders and NCOs to really keep an eye on troops and make sure we're taking care of these young soldiers."
Over the past five years, soldiers under 25 had a far higher rate of cold injuries than older troops, the study showed: 76 per 100,000 "person-years," a term the military uses to include population while factoring in time at risk. By comparison, the rate for soldiers in their early 30s was 38 per 100,000.
The Army overall had the most cases last year of cold-weather injuries at 245 and the highest incident rate at 55 per 100,000 person-years. That was a 26 percent rise over the previous season.
Frostbite, in which skin and underlying tissues freeze, remained the most common cold-weather injury, according to the study. More than 760 soldiers were diagnosed with it over the past five years.
Frostbite is graded in severity similarly to burns, Mease said. It often requires hospitalization, may require surgery and can lead to lasting damage.
"If somebody has a frostbite injury that affects the nerve, that nerve might not function the way it did before it got frozen," he said. "We really want to prevent any of that from happening."
Hypothermia, a drop in body temperature below 95 degrees Fahrenheit, is the most life-threatening of cold-weather injuries. In February 1995, four soldiers in Army Ranger school died of it after spending hours training in chest-deep water in a Florida swamp. Over the past five years, it was diagnosed in soldiers 233 times.
During the same period, the Army reported 217 cases of trench foot, also known as immersion foot, caused by having wet feet for too long.
The study found that rates of frostbite were also markedly higher among African-American troops and female troops. Those differences have been noted in previous studies and suggest that physiologic differences and/or previous cold-weather experience are possible explanations for increased susceptibility.
"It's an interesting finding and it's significant that (commanders) know that," Mease said.
After the Army, the Marine Corps had the highest rate last year of cold injuries, at 46 per 100,000 person-years.
The Navy had the lowest rate at less than 10 per 100,000 person-years.