Shortly after Inc.'s (AMZN) - Get Report acquisition of Whole Foods this summer, Wall Street was quick to raise concern for Costco Wholesale Corporation (COST) - Get Report , the bulk of whose members are also Amazon Prime users.

The overlap may not be a problem after all, a Stifel consumer survey found.

There has been "no material change in membership overlap with Amazon Prime since the Whole Foods acquisition," Stifel analysts wrote in the report published on Wednesday, Oct. 4, "suggesting overlap may be more symbiotic than feared."

Customer loyalty at Costco remain sky-high: overall, 84% of Costco members responding to the Stifel survey said they intend to keep shopping at Costco over the next month—the highest percentage compared to seven other major retailers, including Amazon.

The extent of overlap between Costco and Amazon Prime membership varies across different research firms. Stifel found that the overlap was an average of 36% in the three months prior to the announcement of the Amazon-Whole Foods deal, and 34% in the three months afterward. Cowen & Co. reported in June that the overlap reached over 60% in the second half of 2017.

Whatever that number may be, Costco members remain happy and satisfied it seems. Nearly half of surveyed Costco members rank the store in their top three most frequented grocery stores—that's highest among other retailers and much higher than the 14% for total consumers, Stifel found.

And the cherry on top? Costco members don't plan to shop online as much as Prime members, with an online spending momentum at 33% compared to Amazon Prime's 44%. Stifel also estimated that 44% of total consumers are Amazon Prime members, while 26% are Costco members.

Costco's stock price at $165 as of Wednesday morning reflects a nearly 9% drop since the Amazon Whole Foods deal was announced. The warehouse chain reported in July a 9% year-over-year uptick in sales, TheStreet reported.

More of What's Trending on TheStreet: