The message was delivered in a conference call involving USOC officials and leaders of U.S. sport federations in late January, according to two people who participated in the call, Reuters wrote.
Federations were told that no one should go to Brazil "if they don't feel comfortable going. Bottom line," said Donald Anthony, president and board chairman of USA Fencing.
The USOC's briefing to sport federations is the latest sign that Olympics officials are taking the Zika threat to the games in Rio de Janeiro seriously, and acknowledging that at least some athletes and support staff could face a tough decision over whether to attend.
The United States won most medals at the last Olympics in London in 2012, so any disruption to its presence would be important for the Rio games.
Global health authorities suspect the mosquito-borne Zika virus has caused a spike in Brazil of microcephaly, a birth defect marked by an abnormally small head. As a result, the World Health Organization declared an international health emergency February 1, and the U.S. Centers for Disease Control and Prevention (CDC) is advising pregnant women or those considering becoming pregnant to avoid travel to places with Zika outbreaks.
The USOC's Alan Ashley, its chief of sport performance, and other USOC officials, briefed the leaders of the federations.
Ashley did not respond to email or phone calls requesting comment.
Zika outbreaks have been reported in 33 countries, most of them in the Americas. Symptoms of infection often are mild or imperceptible. But the outbreak in Brazil that began last year has been accompanied by more than 4,000 cases of suspected microcephaly; investigators have confirmed more than 400. The link to Zika is unproven but strongly suspected.