The economic outlook of the nation's top private-sector chief executives dropped to a 16-year low over the first quarter of the year, according to PricewaterhouseCoopers.

Only one in four of more than 250 CEOs surveyed nationwide were optimistic about the U.S. economy, continuing a 12-month slide, the New York-based professional service firm reported.

The outlook on both the domestic and global economy has declined in recent months, though respondents said international sales have yet to be affected by the slumping economy.

Respondents also reported raising prices and reducing spending to keep pace with higher costs.

Ken Esch, a partner at PricewaterhouseCoopers, said despite the downturn fast-growing companies should continue to invest in business development.

"The time and money spent now to develop new products or services for your customers could translate to a strong competitive advantage when the current economic downturn ends," Esch said in a statement.