The Centers for Disease Control and Prevention said Friday that it is monitoring 279 pregnant women with likely Zika virus infections across U.S. states and territories.
The largest number of cases by far are in Puerto Rico, where officials are keeping tabs on 122 pregnant women. But officials said they also are tracking 157 other pregnant women across the country. The numbers include women who have shown symptoms of Zika, such as fever, rash and conjunctivitis, as well as those who remain asymptomatic but have tested positive for the disease.
"One challenge of this Zika virus outbreak is the lack of understanding of the magnitude of risk and the spectrum of outcomes associated with Zika virus infection during pregnancy," researchers wrote in a report Friday. The surveillance effort, they noted, is intended to "enhance risk assessment and counseling of pregnant women and families, advance clinical care, and assist states and territories to anticipate and plan needed resources and increase prevention efforts."
The report does not detail the outcomes of any pregnancies currently being monitored but says that information "will be shared in future reports." Asked about the decision not to include that information, officials cited both privacy concerns and the fact that most of the pregnancies are ongoing. However, Margaret Honein, chief of the CDC's Birth Defects Branch, said fewer than a dozen of the women had reported adverse outcomes so far.
"Most pregnancies are ongoing, so it's hard to appropriately estimate the risk" of complications, Honein said. She added that the agency hopes the current monitoring eventually will provide researchers and the public more information about the risks of Zika on developing fetuses, "but we are not at that stage yet."
The CDC also said Friday that it will begin posting a weekly update on the number of Zika-related pregnancy cases it is monitoring. The numbers are expected to rise as the summer mosquito season approaches.
The CDC and other researchers have concluded in recent months that there is little doubt the mosquito-borne virus can cause pregnancy complications and severe fetal abnormalities, as well as some neurological problems in adults. The most pronounced defect is microcephaly, a rare condition marked by an abnormally small head and a lack of brain development. Hundreds of babies with that devastating condition already have been born in South America, most notably in Brazil, where the current Zika outbreak began last year.
The disease has since spread to dozens of countries and island territories, primarily in South and Central America, as well as the Caribbean. The escalating numbers have prompted the CDC to urge pregnant women in particular to avoid traveling to Zika-affected areas, and to abstain from sexual contact for a prolonged period with anyone who has traveled to countries where the virus is circulating.
Earlier this month, Puerto Rico reported its first Zika-related microcephaly case. A health department statement referred to a male fetus that showed "severe microcephaly and calcifications in the brain accompanied by Zika-wide presence of the virus." It said the case was detected early through "robust surveillance systems," with the abnormalities identified via ultrasound. Health Secretary Ana Rius told reporters in San Juan that the fetus had been turned over to U.S. health officials for testing. She declined to say whether the woman involved had an abortion or miscarried.
In late February, the CDC reported that at least two pregnant women in the United States infected with the Zika virus had chosen to have abortions, while two others had suffered miscarriages. One woman gave birth to an infant with serious birth defects, while two others delivered healthy infants.
At the time, the agency was developing two surveillance systems in conjunction with state and local health officials -- one to monitor people specifically in Puerto Rico, where the virus already was spreading rapidly, and another to monitor cases in the rest of the United States.
With summer temperatures nearly here, U.S. health officials have been warning about expected local outbreaks of the virus in states, particularly in the South and the Southwest. Both regions are home to the Aedes aegypti mosquito, the primary vector for the virus.
Countries such as El Salvador and Jamaica have urged women to consider postpone pregnancy while the outbreak continues.
Friday's news also comes amid the latest push in Congress for more resources to prepare for and combat the spread of Zika domestically. On Thursday, the Senate approved $1.1 billion in emergency funding, substantially more than the $622 million funding package the House approved a day earlier -- in part by using money set aside for Ebola.
The White House, which in February requested $1.9 billion for its Zika response, called the House's measure "woefully inadequate."
President Obama reiterated that stance Friday after an Oval Office briefing on the country's Zika response from CDC director Tom Frieden, Health and Human Services Secretary Sylvia Burwell and Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
“This is something that is solvable. It is not something that we have to panic about, but it is something we have to take seriously… So we've got to get moving,” he told reporters, saying Americans need to urge Congress to move quicker to approve funding. Obama outlined steps the administration is taking to combat the spread of the virus and to develop more efficient diagnostic tests and a Zika vaccine. “All of this work costs money,” he said, calling it “a modest investment” to assure Americans are safe. “And we didn’t just choose the $1.9 billion from the top of our heads. This was based on public health assessments of all the work that needs to be done.”
“Understand that this is not something where we can build a wall to prevent -- mosquitoes don't go through customs,” the president added. “To the extent that we're not handling this thing on the front end, we're going to have bigger problems on the back end.”
As of this week, the United States had 544 reported cases of Zika, nearly all of them involving people who had traveled to countries already plagued by the virus. A handful of infections have been sexually transmitted, but none has yet been acquired from mosquitoes in this country. In addition, there have been more than 800 Zika cases in U.S. territories, the vast majority of those in Puerto Rico, where local transmissions through mosquitoes have been common.
Juliet Eilperin contributed to this report.
This post has been updated.