Illness hit Clinton staff before her pneumonia

WHITE PLAINS, N.Y. -- An outbreak of respiratory illness swept through Hillary Clinton's campaign staff in the weeks before she was diagnosed with pneumonia and fell ill at this year's 9/11 memorial ceremony, campaign aides said Monday.

The Democratic presidential candidate abruptly left Sunday's event after feeling "overheated."

A video later posted on Twitter showed her staggering and slumping forward before being held up by three people as she was helped into a van.

Clinton spokesman Brian Fallon said the former secretary of state began to feel hot at the event, which took place on a muggy day in New York.

There was little shade where Clinton stood amid other dignitaries.

As family members of 9/11 victims read the names of the nearly 3,000 people killed in the attacks, she decided to leave and get a drink of water.

She was wearing a wool suit and had been diagnosed with pneumonia Friday, a fact her campaign had not made public.

In fact, campaign aides said Monday, a number of staff members at her campaign headquarters had fallen ill in recent weeks, including campaign manager Robby Mook.

"I probably came in a few more days than I should have over the last few weeks," he told CNN on Monday. "I'm still actually recovering from the cough that I got through that."