The Centers for Disease Control and Prevention said Wednesday that there are at least “a dozen or so” confirmed cases of Zika virus in residents who recently traveled to countries where the mosquito-borne virus is spreading.

The agency said it was not able to provide an immediate breakdown by state because states must authorize the release of that information. Several state health departments have reported confirmed cases in recent days. These include: Florida, Hawaii, Illinois, New Jersey and Texas. The number of cases is from 2015 to date, CDC spokesman Tom Skinner said.

Health officials said there is no risk to the public because all the cases so far have been in returning travelers who were likely infected by mosquitos abroad rather than by mosquitos in the U.S. mainland.

The CDC and only a few state health departments have the capability to conduct the test to confirm a Zika virus. Many states have been sending samples to the CDC for testing, and that is how the CDC is finding out about potential cases. State health departments are not required to notify the CDC about any cases of the Zika virus. The CDC is in the process of working out a system for collecting information about confirmed Zika virus cases, Skinner said.

Zika is a pathogen carried by mosquitos that typically causes only mild symptoms, but health officials have recently been alarmed because of a possible link between the virus and more than 3,500 children born with microcephaly in Brazil since October. The rare condition, marked by an abnormally small head, is associated with incomplete brain development.

Hawaii health officials say a baby recently born with microcephaly at an Oahu hospital to a mother who lived in Brazil in the spring was infected with the Zika virus in utero.

The New Jersey health department said Wednesday that it was notified by the CDC on Dec. 23, 2015 about an individual who had the illness when she visited Bergen County at the end of November. The woman was exposed in Colombia, and has recovered and returned to that country, according to a a health department statement.

On Tuesday, the CDC released interim guidelines advising obstetricians and other health-care professionals who care for pregnant women to test them for Zika infection if they show symptoms after visiting more than a dozen countries and territories where local transmission of the virus has occurred.

Symptoms include fever, rash, muscle aches or conjunctivitis (pink eye) during or within two weeks of their travel to any of those locations. A positive finding for the virus should be reported to the appropriate local or state health department, CDC said.

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