(Reuters) - U.S. stocks slumped on Thursday with the Dow shedding over 5% and the index on track for its sharpest one-day decline since March 18, as investors fretted over a resurgence in coronavirus infections and a grim economic outlook from the Federal Reserve. The S&P 500 . DJI and the Dow Jones . DJI were set to wipe off most of their gains made this month, and the tech-heavy Nasdaq . IXIC tumbled 3.9% as it came off four consecutive sessions of record highs.