Utility stocks, which are favored by investors in times of volatility for their higher-than-average dividends, were among the few that rose on Wednesday. The Dow Jones utility index, a collection of 15 utility companies, increased 0.5 percent.

There was one positive report Wednesday. The payroll processor ADP said private employers added 213,000 jobs in September, the sixth straight month of gains above 200,000. That survey came ahead of the Labor Department’s report Friday on the job market in September. Economists are forecasting that employers added 215,000 workers last month and the unemployment rate will remain at 6.1 percent.

Despite October’s shaky start, analysts say the next three months may be better.

In recent years, the stock market has risen sharply in the year’s last quarter. The S.&P. 500 rose 10 percent in the fourth quarter last year and 11 percent in the same period in 2011. In 2012, the S.&P. 500 fell in the fourth quarter, but only 1 percent.

News that the first case of Ebola was diagnosed in the United States reverberated through several industries. Airlines were among the hardest hit as investors feared people would travel less. American Airlines fell $1.09, or 3 percent, to $34.39, and Delta by $1.25, or 3.5 percent, to $34.90. Southwest Airlines by $1.22, or 3.6 percent, to $32.55.

Drug makers developing treatments for Ebola rose. Tekmira Pharmaceuticals jumped $3.85, or 18 percent, to $24.99 after it said it might start clinical trials for an Ebola drug this year. NewLink Genetics, another company looking into Ebola treatments, rose $1.53, or 7 percent, to $22.95.