By Dennis Thompson
FRIDAY, Feb. 12, 2016 (HealthDay News) -- At first glance, it seems like a small ray of hope in the ongoing Zika epidemic hitting Latin America.
This, of course, would be good news, given that unborn babies are assumed to bear the primary risk from Zika. The virus has been linked in Brazil to hundreds of cases of microcephaly, a birth defect in which the head and brain are unusually small.
But major public health institutions -- including the World Health Organization, the U.S. Centers for Disease Control and Prevention and the March of Dimes -- say it's too soon to tell whether the Colombia reports are accurate.
Colombian President Juan Manuel Santos stated last Saturday that there's no evidence Zika has caused any cases of microcephaly in his country, though 3,177 pregnant women have been diagnosed with the virus.
CDC researchers are fanning out across Central and South America to gather data on the crisis that has been centered in Brazil, and will independently check Santos' claim, said Dr. Edward McCabe, senior vice president and medical director of the March of Dimes.
"Hopefully, we will have information coming through CDC to confirm or not to confirm" Santos' remarks, McCabe said. "If that statement is true, it would be good news. But then we would be left with why are they seeing microcephaly in Brazil and not in other countries."
Since the Zika epidemic first surfaced in Brazil last spring, the virus has spread to 30 countries and territories in Latin America and the Caribbean. The World Health Organization now estimates there could be up to 4 million cases of Zika infection -- but not necessarily microcephaly birth defects -- in the Americas in the next year.
Santos' statement seems to run counter to a growing body of evidence linking Zika to microcephaly, although the connection has not been proven.
For example, traces of Zika have been identified in the brain tissue of two babies who died from microcephaly, CDC Director Dr. Thomas Frieden told Congress during a hearing Wednesday.
The case involved a European woman working in Brazil who appears to have contracted Zika 13 weeks into her pregnancy. Ultrasound at 29 weeks revealed that her baby would be microcephalic, and a subsequent fetal autopsy found traces of the virus in the brain tissue.
In a statement, the World Health Organization said it may be too soon to tell whether the children of the Colombian mothers will be affected by Zika.
"As in most outbreaks, sometimes cases cannot be detected immediately and investigators are trying to clarify data and contacts as they are reported," the WHO statement reads. "This does not always happen quickly. In any case, Colombia is continuing its work and searching for possible cases of congenital malformations possibly associated with Zika, in case these occur."
Different reporting standards also might complicate the detection of microcephaly, said CDC birth defects epidemiologist Peggy Honein.
"Microcephaly is a difficult birth defect to monitor in populations because there are inconsistent standards of definition and inconsistent use of terminology," she said. "In addition, it is important to remember that surveillance systems in each country may collect their data in different ways."
Both the CDC and the WHO said it may be too soon to tell whether Zika will lead to microcephaly in Colombia.
"The outbreak of Zika virus infection in Brazil occurred earlier than in many other countries, and it is possible that other countries will start to see microcephaly or other adverse pregnancy outcomes later," Honein said.
Months passed in Brazil before a potential link between Zika virus and microcephaly began to show up, the WHO said. Brazil reported its first cases of Zika in May, and reported the first cases of microcephaly in late October.
However, health officials also should not rule out other potential causes for microcephaly as they assess the impact of the Zika epidemic, said Dr. Amesh Adalja, a senior associate at the UPMC Center for Health Security in Baltimore.
"It is still unclear the exact role that Zika may or may not be playing in microcephaly," Adalja said. "Important scientific and statistical work is needed to establish causality. Microcephaly has multiple causes and it will be important to rule out other known causes in cases associated with Zika virus. There is some data pointing to an increase in microcephaly prior to the arrival of Zika in Brazil. This will be important to confirm."