A surgeon from Sierra Leone who was being treated for Ebola at a Nebraska hospital died on Monday, according to the hospital.

Dr Martin Salia, a permanent US resident, is the second patient to die of Ebola in the US. He arrived in Omaha on Saturday, having left Freetown on Friday by air ambulance. He was immediately transported to Nebraska medical center, where he began treatment in the hospital’s biocontainment unit.

Doctors and nurses cared for the ailing surgeon around the clock, the hospital said. At around 4am on Monday Salia’s heart stopped and medical staff were not able to revive him.

“It is with an extremely heavy heart that we share this news,” Dr Phil Smith, medical director of the Biocontainment Unit at Nebraska medical center, said in a statement. “Dr Salia was extremely critical when he arrived here, and unfortunately, despite our best efforts, we weren’t able to save him.”

Experts believe early detection and treatment is critical to surviving the disease which has killed nearly 5,200 people, primarily in Liberia, Sierra Leone and Guinea.

Salia, 44, was not able to walk off the plane, as other patients brought to the US have been able to do. Instead, he was taken off the plane in an isopod, a special device designed to keep contagion from spreading. He was placed on a stretcher and loaded into an ambulance.

He was suffering from advanced symptoms of the deadly disease, including kidney and respiratory failure, when he arrived at the Nebraska medical center on Saturday, the hospital said.

“We are reminded today that even though this was the best possible place for a patient with this virus to be, that in the very advanced stages, even the most modern techniques that we have at our disposal are not enough to help these patients once they reach a critical threshold,” Dr Jeffrey Gold, the chancellor of University of Nebraska medical center, said during a press conference Monday.

The Nebraska medical center is one of four hospitals in the country equipped with biocontainment units and staff highly trained to handle deadly infectious diseases. Salia was the unit’s third Ebola patient. The first two recovered and were discharged.

The hospital said Salia, whose family lives in Maryland, was placed on dialysis, a ventilator and multiple medications to support his organ system. He was given plasma from a surviving Ebola patient as well as ZMapp, an experimental Ebola drug in limited supply.

The blood of those who have recovered from Ebola is believed to help ill patients fight off the infection. The first two patients treated at the Nebraska center were given blood transfusions and survived. The hospital would not say which Ebola survivor donated the blood.

Salia was treating patients at United Methodist Church’s Kissy hospital – which is not an Ebola treatment center – in Freetown when he fell ill. The Washington Post reported that Salia had falsely tested negative for the disease in Freetown, which delayed proper treatment for more than week. The hospital said Saturday was day 13 of the surgeon’s illness. A false negative is not uncommon during early testing because there is very little virus in the body.

Salia’s wife, Isatu, said she was grateful for the efforts of the doctors and nurses who cared for her husband in his final days.

“In the short time we spent here, it was apparent how caring and compassionate everyone was,” she said in a statement released by the hospital. “We are so appreciative of the opportunity for my husband to be treated here and believe he was in the best place possible.”

Salia is the second patient, out of 10 known cases, to die while undergoing treatment for Ebola in the US. The first, a Liberian man named Thomas Eric Duncan, died in Dallas, Texas, in October after initially being misdiagnosed by a local hospital.

His body is due to be cremated, according to guidelines set by the nation’s public health agency, the Centers for Disease Control and Prevention. The bodies of deceased patients are highly contagious, even more so than living patients. An autopsy will not performed because it is deemed too dangerous, the hospital said.

The White House also expressed condolences to Salia’s family, saying the doctor’s death “is another reminder of the human toll of this disease and of the continued imperative to tackle this epidemic on the front lines, where Dr Salia was engaged in his calling.”