SAN FRANCISCO (KCBS) — Blood centers are ramping up ahead of the usual summer shortage, but the Zika virus is cutting into the usual pool of donors.

“In the past four weeks, have you been in any of the following areas on the list where the Zika virus presents?” a blood drive worker asked before drawing blood from a donor in San Francisco.

That question is the new hurdle that seems to be tripping up a lot of potential donors. Blood drives don’t want donors who have recently traveled to South and Central America, Central Africa, or Southeast Asia.

Elizabeth Salmoun with the Blood Centers of the Pacific told KCBS, “That’s one of the hardest things about my job is getting people to come in and donate. One of the reasons is convenience; another is that people are scared of needles, and now we have Zika.”