As U.S. public health officials try to determine whether Zika has arrived in the country, doctors are establishing guidelines on how to care for the rising number of babies whose mothers were infected with the virus during pregnancy.
Florida this week said it is investigating a case of Zika not related to travel to an area where Zika is active, raising the possibility of local transmission.
So far, more than 400 pregnant women in the continental United States have evidence of Zika infection, up from 346 from a week ago, the U.S. Centers for Disease Control and Prevention reported on Thursday. All of those were related to travel or sex with an infected person who had traveled.
Three more babies have been born in the United States with birth defects linked to Zika infections in their mothers, bringing the total to 12, CDC said.
Zika has been proven to cause microcephaly, a severe birth defect marked by small head size and undersized brains that requires a complex network of care providers and social workers to treat and provide support to parents.
But microcephaly is just the tip of the iceberg, according to experts speaking at a CDC-sponsored workshop on Thursday. They said many babies exposed in utero who appear normal at birth may have developmental problems down the road, including hearing and vision problems.
For example, babies born with a functional sucking reflex may never develop the ability to swallow and will need to be fed through a feeding tube. These infants will have a higher risk of pneumonia, said Dr. Edwin Trevathan, a pediatrician and child neurologist at Vanderbilt University Medical Center.
Less obvious damage to structures on only one side of the brain may cause seizure disorders that do not appear until adolescence, Trevathan said.
Pediatric experts at the workshop are reviewing the potential consequences of Zika infection and plan to make recommendations on ways to treat Zika-exposed infants.
The connection between Zika and microcephaly first came to light last fall in Brazil, which has now confirmed more than 1,600 cases of microcephaly that it considers to be related to Zika infections in the mothers.
The recommendations come as Florida officials investigate what may be the first case of Zika in the continental United States caused by the bite of a local mosquito.
Florida officials will not elaborate on how a resident of Miami was infected and whether the case was related to mosquitoes.
"We continue to investigate and have not ruled out travel or sexual transmission at this time," Florida spokeswoman Mara Gambineri said in an email on Thursday. However, she said the state still suspects the case is not related to travel to a Zika-infected area.
The White House on Wednesday released a statement saying President Barack Obama had spoken to Florida Governor Rick Scott regarding a suspected case of mosquito transmission of Zika and promised more money to fight the virus.
At the Zika workshop, Dr. Marc Fischer, chief of surveillance and epidemiology activity at the arboviral diseases branch of the CDC, said the agency has worked with state health departments to establish strategies to identify possible local transmission in the United States.
"When and if there is a case of local transmission, we work with local health departments to identify additional cases to define the geographic scope of the outbreak," he said.
That includes surveying households and neighbors within a 150-yard radius around the residence of the person who has Zika.
"That's basically the flying radius of the vector mosquitoes," he said.
According to the U.S. Zika response plan, Zika local transmission is defined as two or more cases not due to travel or sex with an infected person that occur in a one-mile diameter over the course of a month.
CDC has given Florida $2 million for Zika preparedness, and on Thursday awarded another $5.6 million to assist the state with Zika as part of an additional $60 million in Zika funds to states announced on Thursday. U.S. lawmakers so far have not approved any of the White House's $1.9 billion request for Zika.
CDC plans to award another $10 million to states and territories on Aug. 1 to speed identification of microcephaly and other birth defects linked to Zika.