A mixed batch of economic data Wednesday and concerns over the first reported case of Ebola in the U.S. triggered one of the biggest stock sell-offs in months. The Nasdaq composite, down 1.6%, fell definitively below its key 50-day moving average for the first time since April 4. The S&P 500 dropped 1.3%. The IBD 50, a proxy for high-growth stocks, lost 2.5%. The Dow utilities, often a gauge of investor defensiveness, rose 0.4%.