The CDC said several of these cases are among pregnant women, although it did not specify how many.
"These new reports suggest sexual transmission may be a more likely means of transmission for Zika virus than previously considered," the CDC said in a written statement.
Two of the cases are in women whose only known risk is sexual contact with a male partner exhibiting symptoms of the virus after returning from an infected area, according to the CDC.
Lab results are pending for four additional suspected cases among women. There are eight other suspected cases under investigation.
The CDC is working with state health officials to investigate all of these cases. Officials have not said which states they are working with or where these women live because the risk applies to all women in the United States, according to Dr. Jennifer McQuiston, deputy incident manager for Zika virus at the CDC.
"We have been a little surprised by the number of suspected cases we've received," she told CNN.
The CDC is urging individuals to follow its previously issued guidance
of abstinence or condom use for women,
especially those who are pregnant, whose male sexual partners have traveled to a Zika-infected area. It also issued a notice through their Health Alert Network that notified health care providers, labs and local, state and federal public health employees about urgent public health information.
The recommendations single out partners of pregnant women because the virus has been linked to the neurological birth defect microcephaly
. Infants with the disorder have unusually small heads and sometimes developmental delays that vary in severity.
The CDC restated there is no evidence that women can transmit the virus to their sexual partners and that the most likely way to become infected with the Zika virus is from infected mosquitoes.
In February, the CDC confirmed
the virus had been transmitted to the sexual partner of an individual in Texas who had traveled to a Zika infected area -- a first for this outbreak but not a first in and of itself. The first known case of sexual transmission
of the Zika virus was occurred in 2008, when a microbiologist from Colorado State University returned from Senegal, reunited with his wife and infected her with the virus.
"The report of the case in Dallas raised concern so doctors are beginning to think about it when they see patients," McQuiston said, adding that another possible reason for the increase in these possible cases could be reflective of the travel patterns and people returning from infected areas.