Doctor's death marks second US Ebola fatality

(CNN) -- Marking the second Ebola death in the United States, Dr. Martin Salia died at around 5 a.m. ET Monday, according to Nebraska Medicine spokesman Taylor Wilson.

A legal permanent resident of the U.S., Salia was working in West Africa when he contracted the virus.

Salia arrived Saturday at Nebraska Medical Center in Omaha. The hospital tweeted Monday that he was 'extremely critical' when his treatment began and 'unfortunately, despite our best efforts, we weren't able to save him.'

Salia was suffering from advanced symptoms of Ebola, including kidney and respiratory failure, health officials said.

CNN's Shawn Nottingham contributed to this report.