ISSAQUAH, Wash. — Costco Wholesale Corp. posted net sales growth of 5.7% for its second quarter as more members visited its warehouse clubs and spent more per trip.

Traffic was up 4.3% in the United States and 5.3% companywide, Costco reported on March 7.

Net income in the period through February 18 was $1.74 billion, up from $1.47 billion in the comparable period a year earlier. Comparable-store sales increased 4.3% in the United States and 5.6% overall. Costco said comps at its e-commerce operations increased 18.4%.

Rich Galanti, who retired as the company’s chief financial officer this month, said that Costco is not ready to raise its membership fees but that it is cracking down on membership sharing by more frequently checking on membership cards in its clubs. That effort has led to an uptick in new members, Galanti said.

Costco has 875 warehouses, including 603 in the United States and Puerto Rico. Costco has clubs in a dozen other countries. The company opened four clubs in the second quarter, including three in the U.S. and one in Shenzhen, China.

For the four-week reporting month of February, which ended March 3, the company reported net sales of $18.2 billion, an increase of 6.9% from $17.04 the previous year. Net sales for the first 26 weeks were $123.15 billion, up 6.1% from last year.