The Standard & Poor’s 500 index declined for the fourth time in five sessions, as biotechnology shares tumbled while media companies sold off on disappointing results from Viacom Inc. and 21st Century Fox.

The Nasdaq biotechnology index dropped 4 percent Thursday, snapping a five-day winning streak. Viacom and Fox slumped at least 6.4 percent after joining a parade of media companies reporting disappointing results. Keurig Green Mountain plunged 30 percent after cutting its sales and profit forecasts. Transocean and Michael Kors added at least 10 percent after posting better-than-estimated results.

The S&P 500 lost 0.8 percent to 2,083.56, falling below its average prices during the past 50 and 100 days. The Dow Jones industrial average fell 120.72 points, or 0.7 percent, to 17,419.75. The Dow fell for a sixth day, its longest losing streak since October. The Nasdaq composite index decreased 1.6 percent, the most in almost a month.

“It’s like panic buying and panic selling,” said Walter Todd, who oversees about $1.1 billion as chief investment officer for Greenwood Capital Associates. “The reactions you’re seeing in the marketplace are just very violent for companies reporting earnings, sometimes to the upside, sometimes to the downside.”

About 85 percent of S&P 500 members have released earnings figures, with three-quarters beating profit estimates and half topping sales projections. Analysts now call for a 2.8 percent drop in second-quarter earnings, shallower than July 10 estimates for a 6.4 percent fall.

The S&P 500 is coming off its best monthly gain since February, and closed Thursday 2.2 percent below its record set in May.

The Chicago Board Options Exchange Volatility Index rose 10 percent Thursday to 13.77.