NEW YORK - Shares of Costco (COST) fell Wednesday, a day after the warehouse club operator reported results for its fiscal first quarter that missed Wall Street expectations.

The company also said that sales at stores open at least a year, considered a key measure of a retailer's health, fell 1 percent in the quarter. It said falling gasoline prices and unfavorable foreign exchange rates were to blame for the drop. Excluding those factors, sales at stores open a year would have risen 6 percent.

Costco reported net income of $480 million, or $1.09 per share, down from$496 million, or $1.12 per share, in the same period last year. Analysts had expected earnings of $1.17 per share, according to FactSet.

Revenue rose 1.3 percent to $27.2 billion, below the $27.6 billion analysts expected.

Costco, based in Issaquah, Washington, operates nearly 700 stores.

Shares of Costco Wholesale Corp. fell $9.52, or 5.6 percent, to $159.35 in afternoon trading Wednesday. Its shares are up more than 12 percent since the beginning of the year.