The 65-year-old Clinton, who's expected to leave her job soon after serving as America's top diplomat during President Barack Obama's first term, is recovering at home after the incident last week and is being monitored by doctors, according to a statement by aide Philippe Reines.
No further details were immediately available.
The statement said Clinton was dehydrated because of the virus and that she fainted and sustained a concussion. She will continue to work from home in the week ahead and looks forward to being back in the office "soon," the statement said.
Congressional aides do not expect her to testify as scheduled at congressional hearings on Thursday into the Sept. 11 attack against a U.S. diplomatic outpost in Benghazi, Libya, that killed four Americans, including the U.S. ambassador.
The aides spoke on condition of anonymity because they weren't authorized to publicly discuss Clinton's status.
The Senate Foreign Relations Committee and the House Foreign Affairs Committee had planned to hear from Clinton, and department officials had taken steps to set the stage for her appearance, with Tom Nides, a deputy secretary of state, briefing some members of the House committee staff about her testimony.
Clinton backed out of a trip to North Africa and the Persian Gulf on Monday because she was sick. She caught the virus during a recent visit to Europe.
She's known for her grueling travel schedule and is the most traveled secretary of state, having visited 112 countries while in the job.
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