Almost 60 percent of the infected adults are women.
Researchers said the study results could not be used to predict whether the immunoglobulin treatment would benefit infected adults.
Although costly, treatment as also needed for already infected adults to ease suffering and prolong life.
It is also possible, experts said, she had been sexually molested by an infected adult.
There are now an estimated 10 million infected adults, and more than 366,000 cases have been reported in 162 countries.
It takes years for symptoms to appear in many infected young adults, and they may feel well for most of their fertile period.
They've had cases that were outside the norm, including infected adults.
The numbers of infected adults with underlying medical conditions that make them more susceptible to infection increased during the study.
A young survivor named Small Sam is kidnapped by infected adults and taken away.
It said that of the 22.3 million infected adults below the Sahara, 55 percent are women.