New York is expanding free Zika virus testing to pregnant women who had unprotected sex with a partner who had travelled to a Zika-infected area.
The state already offers testing to pregnant women who travelled during pregnancy to an area where Zika is circulating, and to non-pregnant women, men or children who developed symptoms of Zika within four weeks of travel to an area with active Zika transmission.
Only one in five people infected with the Zika virus will develop symptoms, which are typically mild, but there have been increased reports of a birth defect known as microcephaly, a condition defined by unusually small heads that can result in developmental problems.
Much remains unknown about Zika, including whether the virus actually causes microcephaly.
Dr Howard Zucker, commissioner of New York's health department, said the department is expanding testing "as evidence has emerged that the risk of sexual transmission is greater than previously known".
The department is investigating one possible case of sexual transmission.
It recommends, along with the Centers for Disease Control and Prevention, that men who have travelled to or lived in an area with active virus transmission abstain from sex or use condoms throughout their partner's pregnancy.
The department is also working with local health officials in counties inhabited by a type of mosquito that could potentially carry the Zika virus to update and implement a mosquito surveillance and response plan.