NEW YORK, Oct 1 (Reuters) - Utility shares rallied on Wednesday, the only one of the ten primary S&P 500 sectors in positive territory, as investors sought protection amid uncertainty over the first patient to be diagnosed with Ebola in the United States.
The group, considered a defensive play for its high yields, rose 1.3 percent on high volume, led by Exelon Corp, which added 3.4 percent to $35.26, and NRG Energy, up 2.7 percent to $21.30. Both stocks were on track to outpace their 50-day average volume.
Options trading for the group was also heavier than normal, wrote Andrew Wilkinson, chief market analyst at Interactive Brokers in Greenwich, Connecticut.
"By midday on Wednesday, [Exelon's] options volume was about 27 percent higher than its 10-day average. Likewise Duke Energy Corp and Consolidated Edison Inc and Edison International were each comfortably ahead of their average daily options volume," he wrote.
Index snapshot at 13:02 EDT:
* S&P 500 was falling 19.82 points, or 1 percent.
* Nasdaq Comp was losing 60.13 points, or 1.34 percent.
* Dow industrials was dropping 209.23 points, or 1.23 percent.
* Russell 2000 was falling 12.5 points, or 1.13 percent.
* S&P MidCap was dropping 13.04 points, or 0.95 percent.
* S&P SmallCap was losing 6.45 points, or 1.02 percent. (Editing by Nick Zieminski)