A woman who had her pregnancy test negative for Zika and other sexually transmitted diseases may have been infected with another virus or had a viral test negative before the result came back negative, a new report has revealed.
Dr. Joanna C. Brown, an infectious disease physician at Brigham and Women’s Hospital in Boston, said a new study released Thursday found that more than a quarter of women tested positive for Zika after their second Zika test.
A new report released Thursday said that a majority of pregnant women who had their second test positive for the virus after a second test negative after a third test were infected with Zika virus, a sexually transmitted disease.
The results were reported in the latest issue of the journal JAMA Infectious Diseases.
The study is one of the first to look at how often pregnant women have been tested for the Zika virus and other viruses after they have given birth.
It was conducted by Brown and her team at the hospital, which is based at Boston Children’s Hospital.
The first study published by the Johns Hopkins University School of Medicine in March revealed that the Zika outbreak was linked to the first Zika test in January, which showed a pregnancy test for Zika negative.
A second study published in June found that the same outbreak linked to a Zika test result in December, and a third study published this month, published in the journal Science, linked the two outbreaks.
A number of new Zika virus infections have been detected in the United States since December, according to the CDC.
The first case was diagnosed in February in San Francisco.
The second was confirmed in March in Miami.
The CDC reported that the first case of Zika virus in a U.S. pregnant woman was confirmed at the end of March, and it was confirmed by the World Health Organization in April.
The other study published Thursday by Brown, Dr. Christopher D. Schacter and colleagues, also found that nearly a third of women with Zika test negative at the time they received their second prenatal test, and that more women were infected after the third test result came in negative.
Most women who received a second Zika infection test positive were infected at the same time as their third Zika test positive result, Brown said.
In other words, the virus was transmitted at a point when the women were most likely to have the virus.
The findings were consistent with what has been observed in other studies, including a study published last year by the American Society for Microbiology in which researchers found that between 40 and 50 percent of women who tested positive after a first Zika infection had the virus in their second result, and 40 to 50 percent had the viral infection in their third result.
Brown said she does not know how many women who have had their third test negative are infected with other sexually transmissible diseases.
“We know that in the U.K. and other countries, many of those women have had tests positive, but many of them are not, so we have to be very careful about who is infected with these other viruses,” Brown said in a statement.
She said she did not know whether a woman with a third Zika infection may have had a test positive first.
“It is important to remember that the third results are not necessarily conclusive,” she said.
Brown, who is also the director of the CDC’s Zika Response, said she was surprised that the number of women in the study who tested negative after the second test result was so high.
“I thought that would be a lot lower than what it is, and yet they found that a third result is the threshold for having a third infection,” she told CNN.
“This is a very high percentage of women.
We really need to make sure we do a lot of testing before we make a decision to test for a third virus.”
She said the study did not find that all women tested negative for the viruses after their third results.
“It was the percentage of people who were infected that was not statistically significant, but it does show that this is an important milestone in the Zika epidemic,” Brown added.
She did not have information about the types of other viruses in the women who were tested.
Brown and her colleagues said that, if the women did have other sexually transmmissible diseases, they should have been screened before having a second pregnancy test.
They also said that if a woman had a third negative result, she should have received a Zika virus test in addition to a third pregnancy test and a second virus test, to see if the virus spread in her bloodstream.
“If you have a third or fourth negative result with a second, you should get a second and a Zika vaccine and follow the guidelines and instructions,” Brown explained.
“If the third negative results were not detected, you need to get a third vaccine and a virus test to see what happened.”