Confirmed: Zika Virus Causes Birth Defects

ST. CROIX — Officials at the Centers for Disease Control and Prevention said on Wednesday that there was now enough evidence to definitively say that the Zika virus could cause unusually small heads and brain damage in infants born to infected mothers, according to the New York Times.

The conclusion should settle months of debate about the connection between the infection and these birth defects, called microcephaly, as well as other neurological abnormalities, C.D.C. officials said.

“There is no longer any doubt that Zika causes microcephaly,” said C.D.C. Director Dr. Thomas R. Frieden. He said the conclusion, reached after evaluating “mounting evidence from many studies,” signifies “an unprecedented association” in medicine.

“Never before in history has there been a situation where a bite from a mosquito can result in a devastating malformation,” Dr. Frieden said.

The C.D.C. officials said they hoped that the announcement increased awareness and concern about the potential threat to Americans who travel to affected areas in Latin America and those living in Puerto Rico, American Samoa and Southern states where the virus is expected to arrive this summer.

The announcement may increase pressure on Congress to allocate more than $1.8 billion in emergency funding that President Barack Obama requested for prevention and treatment of the outbreak. While C.D.C. officials did not address funding, Dr. Sonja A. Rasmussen, the agency’s director of public health information and dissemination, said the conclusion “emphasizes the importance of working on ways to prevent Zika infection,” including efforts to develop a vaccine.

“Surveys have told us that a lot of people aren’t concerned about Zika virus infection in the United States — they don’t know a lot about it,” Dr. Rasmussen said.

“Now that we can be more convincing that Zika virus does cause microcephaly, we hope that people will focus on our prevention messages more closely.”

The C.D.C. analysis, led by Dr. Rasmussen, was published Wednesday in The New England Journal of Medicine, and involved weeks of research into findings that have emerged from Brazil and elsewhere, including studies of fetuses with microcephaly in pregnant women infected with Zika.

The authors said they used established frameworks for assessing whether evidence met scientific criteria proving that one factor causes another. Those criteria included the existence of cases of microcephaly that have been strongly linked to documented exposure to Zika virus. Dr. Rasmussen and her colleagues also reviewed the biologically plausible explanations for how the virus might cause damage to the brain, and the absence of other explanations that make sense.

About 700 people in the United States have been infected with the Zika virus as of last week, including 69 pregnant women, Dr. Anne Schuchat, the deputy director of the C.D.C., said on Monday at a White House briefing. About half of the cases are in Puerto Rico, where the virus is circulating locally. Most of the other American cases have occurred in people who traveled to South America. There have been 14 confirmed Zika cases in the U.S. Virgin Islands, with the first positive test of the virus in a pregnant woman coming last Tuesday.