The federal government wants doctors to run more tests on infants born to mothers possibly infected with the Zika virus, which is spreading in Miami.

The Centers for Disease Control and Prevention updated its clinical guidance on Friday to reflect new information on the virus. It is giving doctors new information on how to interpret laboratory testing on infants and it wants doctors to increase their vigilance in examining the babies through repeated eye and hearing tests and ultrasounds.

More than 500 women have shown evidence of the Zika virus across the U.S., with 16 infants having birth defects, according to CDC data as of Aug. 11.

In the U.S. territory of Puerto Rico, the virus has been spreading via mosquito bites for some time. A new study published Friday estimates that up to 10,300 pregnant women could have been infected with Zika during the initial outbreak.

Of those 10,300 women, up to 270 could give birth to a child with microcephaly, a birth defect linked to Zika from mid-2016 to mid-2017. The birth defect causes babies to be born with abnormally small heads.

The new CDC recommendations come as Zika spreads through mosquito bites in a small part of Miami. Florida health officials have found 35 cases of non-travel related Zika infection, most likely from mosquito bites that are the primary way the virus spreads.

State health officials say they believe the virus is spreading in a less than one-square-mile area of Miami. In recent days, officials have found several cases of people who got Zika and were located outside of that area.