Some 157 pregnant women in the United States and another 122 in U.S. territories, primarily Puerto Rico, have tested positive for infection with the Zika virus, the U.S. Centers for Disease Control and Prevention said on Friday.
The CDC, in a conference call, said that so far fewer than a dozen of the infected pregnant women it has tracked in the United States and Puerto Rico have had miscarriages or babies born with birth defects.
CDC officials said the agency will now report on a weekly basis all pregnant women in the United States and its territories who have any laboratory evidence of potential infection, regardless of whether virus symptoms are present, whereas previously its tracking focused on symptomatic cases.
Officials believe only about 20 percent of people with Zika display common symptoms, such as fever, rash, joint and muscle pain and red eyes.
The data will be compiled from a pregnancy registry in the United States and a similar surveillance system set up in Puerto Rico, where officials are expecting hundreds of thousands of Zika cases.
USA Swimming said on Friday it has moved a pre-Olympic training camp from Puerto Rico to an aquatic center in Atlanta due to concerns about Zika, but does not expect the virus to keep the team from competing at the Rio Games in August.
Two weeks earlier, Major League Baseball said it would relocate two games that were set to be played in Puerto Rico due to concerns among players over the Zika virus in the area.
U.S. health officials have determined that the mosquito-borne virus, which can also be transmitted through unprotected sex with an infected person, can cause microcephaly, a birth defect marked by unusually small head size, and can lead to severe brain abnormalities and developmental problems in babies.
The inclusion of asymptomatic cases “casts a broad net to make sure we are monitoring all pregnant women who may be at risk for poor outcomes associated with Zika,” said Dr. Margaret Honein, chief of the agency’s birth defects branch.
The decision follows reports of miscarriages and babies born with birth defects to women who had no recollection of having experienced Zika symptoms, she said.
Honein said it is not yet possible to estimate from the two surveillance systems the risk of adverse outcomes among pregnant women, but added that it eventually will be.
The agency told reporters on the call it has dramatically increased its testing capacity for Zika in the United States as it girds for an increase in cases during the summer mosquito season, when Gulf coast states such as Florida, Louisiana and Texas are expected to be on the front lines of local transmission.
Virtually all the Zika cases in the continental United States so far have been in people returning from countries where Zika is prevalent, such as Brazil, or through sexual transmission by such travelers.
The latest report comes at a time when U.S. health officials have been clamoring for adequate funding to support mosquito protection and eradication, development of anti-Zika vaccines and better diagnostics, and long-term studies needed to follow children born to infected mothers and to better understand the sexual transmission risk.
President Barack Obama on Friday urged the U.S. Congress to pass a bill to boost emergency funding to deal with Zika, saying it was critical for U.S. citizens thinking about having children to be assured about the government’s response.
“It needs to get me a bill that has sufficient funds to do the job. They should not be going off on recess before this is done,” Obama said after a meeting with top health officials.
The Obama Administration has requested $1.9 billion in emergency Zika funding. The U.S. Senate has approved $1.1 billion of that request. The U.S. House of Representatives, however, voted to allocate $622.1 million financed through cuts to existing programs, such as for Ebola, which U.S. health officials have called inadequate and shortsighted.
The World Health Organization has said there is also strong scientific consensus that Zika can also cause Guillain-Barre, a rare neurological syndrome that causes temporary paralysis in adults.
The connection between Zika and microcephaly first came to light last fall in Brazil, which has now confirmed more than 1,300 cases of that it considers to be related to Zika infections in the mothers.