NEW YORK — The number of pregnant women in the United States infected with Zika virus is suddenly tripling, due to a change in how the government is reporting cases.
NEW YORK — The number of pregnant women in the United States infected with Zika virus is suddenly tripling, due to a change in how the government is reporting cases.
Previously, officials had reported how many pregnant women had both Zika symptoms and positive blood tests. In a change announced Friday, the Centers for Disease Control and Prevention’s count will include all women who tested positive, regardless of symptoms.
There are now 157 pregnant women infected with Zika in the 50 states, up from the 48 reported last week under the old definition.
Experts emphasized that there does not appear to be any dramatic actual increase of pregnant women with the disease in recent months. There was a spike in diagnoses in February and March, but relatively few new cases since then, according to CDC data that includes women who experienced symptoms and those who didn’t.
The Zika virus causes only a mild and brief illness, at worst, in most people. But in the last year, infections in pregnant women have been strongly linked to fetal deaths and to potentially devastating birth defects, mostly in Brazil.
The virus is spread mainly through the bite of a tropical mosquito called Aedes aegypti. It can be found in the southern United States, but there’s no evidence that they’ve been spreading the virus in the U.S. yet. All the 544 total cases in the 50 states so far have been people who had traveled to outbreak areas, or who had sex with someone who did.
Experts think mosquitoes on the U.S. mainland will probably start spreading the virus in the months ahead, when hot weather hits and mosquito populations boom.
The sudden rise in the count of pregnant women with the disease in the U.S. may seem jarring. But Dr. Neil Silverman, a UCLA professor of obstetrics who has been advising the California Department of Public Health on Zika issues, explained the change in method does not indicate a greater risk of infection.
When he gets calls from patients, he said, “About 90 percent of what we’re doing is reassuring and calming people.”
Only an estimated 1 in 5 people infected with Zika develop symptoms — fever, rash, joint pain, and red eyes — which usually last no more than a week.
Initially, doctors recognized the connection between the virus and birth defects only in women who had suffered symptoms during pregnancy. But reports published this year indicate some pregnant women with laboratory evidence of a recent Zika infection — but who never had symptoms — have delivered infants with these defects.
International health agencies have already been reporting Zika infections in women based solely on lab tests. Some experts have found it surprising that the CDC has been basing its official number on a more conservative case definition.
However, CDC officials had voiced concerns that one kind of blood test is too prone to giving a false positive test result if a woman was infected with a different but similar tropical virus.