BRAZIL: Fewer Zika Microcephaly Cases Than Previously Reported

Brazil is enduring an extraordinary outbreak of microcephaly, a rare birth defect that results in infants being born with abnormally small heads and brains. Since last fall, more than 4,000 suspected cases have been reported, and authorities have blamed an unusual virus, Zika, carried by mosquitos.

But now it appears that a number of those cases may not in fact be microcephaly, or not linked to Zika.

On Wednesday, Brazil’s Ministry of Health said 4,180 cases of Zika-related microcephaly had been reported since October. The country is trying to find out which cases it could actually confirm from notifications provided by doctors – a slow and complicated process as the information is compiled and checked by health secretariats in 26 states and one federal district spread across South America’s biggest country.

After experts scrutinized 732 of the cases they found that more than half either weren’t microcephaly, or weren’t related to Zika.

Just 270 were confirmed as microcephaly that appears to be linked to Zika or other infectious diseases, according to the latest ministry bulletin.

It’s not yet clear whether the same pattern will emerge from the rest of the 3,448 cases that Brazil has to examine. And health experts say the huge number of cases is still very worrisome — as is the rapid spread of Zika through the Americas. (Brazil reported just 147 cases of microcephaly in 2014).

Microcephaly causes babies to be born with abnormally small heads, and can cause motor and learning difficulties, among other problems. The condition can also be caused by genetic factors or drug or alcohol abuse during pregnancy.

Some scientists said the new data suggest that Brazil will have fewer cases of Zika-related microcephaly than originally feared. The country may have over-counted microcephaly cases because it initially asked doctors to report all births of babies with a head circumference of 33 centimeters or less — but some of those were simply children with normally small heads.

“It is possible that the number of cases of microcephaly with suspected relationship to Zika will be much less,” said Esper Kallas, an infectious diseases specialist and professor of medicine at the University of São Paulo. “I think it will be less than a third” of the possible cases that have been reported, he said.

Kallas also said the outbreak had made Brazil realize that microcephaly unrelated to Zika was more common than authorities realized in the past.

Other specialists, though, were wary of the new data, questioning the methodology that was being used. They noted that authorities in one of the badly affected areas, the northeastern state of Bahia, have used relatively cheaper transcranial ultrasound imaging — rather than CT brain imaging scans — to try to confirm and discard cases of microcephaly.

The more inexpensive test might not spot milder cases of the condition, said Ganeshwaran Mochida, a pediatric neurologist and researcher at Boston Children’s Hospital. “There could be some cases mistakenly discarded due to not enough sensitivity,” he said.

Zika was first confirmed in Brazil in May last year, and has spread rapidly in the hemisphere, reaching 23 countries and territories. Its explosive growth has alarmed health professionals who worry about the suspected linkage to microcephaly and a rare nervous system syndrome known as Guillain-Barré that can lead to paralysis.