They are searching for new mothers in the hope of solving one of the world's most urgent public health mysteries: Is the Zika virus really causing microcephaly, a birth defect that leaves babies with shrunken heads and badly damaged brains?
"The preponderance of evidence points to Zika being the culprit," says Megumi Itoh, an epidemic intelligence officer with the U.S. Centers for Disease Control and Prevention who is part of the four-member team. "But we don't know for certain yet. So this is one way of finding that out."
The team, which also includes representatives from Brazilian federal and local health departments, is helping launch the biggest study yet of Zika and its suspected link to microcephaly. A total of eight U.S.-Brazilian investigative groups are working for the next few weeks to track down more than 100 women who had babies with microcephaly since the Zika outbreak began.
Additionally, the teams will try to find hundreds of mothers who had healthy babies at about the same time for comparison. The idea is to produce the most convincing evidence yet as to whether Zika is really causing microcephaly and, if so, how often and how severely. It's unclear when the research might produce results, but it could possibly be as early as the spring.
Even though Joao Pessoa, which is on the northeast coast of Brazil, is part of the epicenter of the Zika outbreak, the investigators know that finding these women will not be easy. And the teams are under intense pressure to work fast to help Brazil — and the rest of the world — gain a better understanding of just how much of a threat is posed by the Zika virus.
On Tuesday, when Itoh and the other teams began their work, a handful of journalists accompanied their first forays. The experience illustrates the difficulties they'll face.
When Itoh's team arrives at the clinic, for example, a health worker gives them the disappointing news that the first mother on their list is working all day. So there's no way to contact her today.
The team asks about the next name. More bad news. The clinic workers don't think she'll cooperate because she's upset that she hasn't received the results of her Zika testing yet. The team decides to go to her house anyway.
Even though it's supposed to be the dry season, it's pouring rain. Everyone runs to the car.
The rain has let up a little when the group arrives at the woman's house, but now it's really starting to get hot and sticky. The person who answers the intercom says the mother's not home. As the team heads back to the car, Itoh acknowledges the day has been disappointing but not surprising.
"I think it's, you know, par for the course," she says.
After a quick lunch and stop at another health clinic for more guidance and advice, the team drives to the home of a third woman, Camila Alves. She's not there when the team arrives at the front door of her small brick house on a narrow cobblestone street. But her grandmother welcomes the group in, and her cousins and other family members offer chairs in their small courtyard to wait.
Finally, Alves comes in with her baby. She's young, just 22, petite, with dark brown hair pulled back and dark brown eyes. She's carrying her daughter, Maria, who at first glance looks like a normal 2-month-old. But as Alves sits down in a rocker, she turns her baby toward the visitors. Maria's forehead seems to just kind of disappear. Her head is tiny.
Itoh's Brazilian counterpart, Marcia Andrade, starts running through page after page of questions.
Did Alves get any other infections when she was pregnant that may have caused the microcephaly? Toxoplasmosis? No. Cytomegalovirus? No. Syphilis? No.
Then the next set of key questions: Was she exposed to any toxins? Pesticides? Insecticides? Rat poison? No. No. No.
Andrade takes a deep breath when she gets to a really important part: Did Alves have any Zika symptoms early in her pregnancy?
Do you remember having a fever? A rash? Joint pain? Yes, Alves says. She had a fever, and yes, a rash too. Probably in the first trimester, suggesting that maybe, just maybe, yes, she did have Zika.
After more than an hour of questioning, the investigators ask Alves if they can take Maria into the nursery so Itoh can measure the circumference of the baby's head with a tape measure. It looks like Maria has a severe case of microcephaly. Itoh also takes pictures of the baby lying in her crib.
Next, a technician takes a blood sample from Alves, then inserts a needle into Maria's tiny arm to draw some blood from her as well.
Everyone cringes as the baby cries. Alves has to step outside. But finally, they're done.
The researchers will send the blood back to the United States for detailed analysis to try to pinpoint whether Alves and her baby actually had Zika. If so, that would strengthen the link between Zika and microcephaly.
When everything's done and Maria's calm again, Alves explains why she decided to volunteer for the study.
"I wanted to know if she really was born this way because of Zika," says Alves. "It's difficult not to know why your baby's born this way. ... Nobody knows why babies are turning out like this."
She also hopes the answer will make the Brazilian government do more.
"I want the government to do something to combat this so more children aren't born like this," she says. "It's hurting a lot of children and a lot of families."
As the investigators are leaving, Itoh reflects on how things went.
"I think it went very well. We accomplished everything we came here to do," she says. "The mother was very gracious."
The investigators obviously need to track down many more patients, she notes, adding: "This is just the beginning."