This stark statistical reality was discovered by a team of researchers from Brazil's Oswaldo Cruz Foundation, which analyzed hospital records across Brazil from 2008, well before Zika arrived, until the end of February 2016.
The researchers also looked for data on rare, potentially deadly inflammations of the brain and spinal cord such as encephalitis, myelitis, and encephalomyelitis, as well as Guillain-Barré syndrome
, a disorder where the body's immune system attacks its own nerve cells, causing pain, paralysis and even death.
The results, published in the Centers for Disease Control and Prevention journal Emerging Infectious Diseases
, found "an unprecedented and significant rise in the hospitalization rate for congenital malformations of the nervous system, Guillain-Barré syndrome, encephalitis, myelitis and encephalomyelitis" beginning in mid-2014.
That's more than a year before the world became aware of the outbreak in October 2015, and stories of Zika's terrible consequences began to appear in the news.
Epicenter of Zika hardest hit
The numbers show the northeast region of Brazil, often considered the epicenter of the Zika outbreak, was indeed the hardest hit. Historical averages of congenital malformations were stable at about 40/100,000 live births until November of 2015. Then the number jumped to 170/100,000 births, four times higher.
Then, in the four months between November 2015 and February 2016, "a total of 1,027 hospitalizations for congenital malformations of the nervous system were recorded nationwide," the researchers said. Almost half, 448, occurred in the Northeast.
Rates of Guillain-Barré and encephalitis, myelitis and encephalomyelitis showed a similar increase in the Northeast. Hospitalizations for Guillain-Barré increased by nearly 3% until the outbreak peaked in July of last year, while the Northeast was the only area of the country to see an increase in CNS.
No one really knows why this section of Brazil was so unfortunate.
"It might be the economic environment," one researcher told CNN's Chief Medical correspondent Dr. Sanjay Gupta, during his visit to the northeastern city of Salvador just before the Olympic Games in Rio.
"Because of the poverty, we have a more closely packed population, and sanitary conditions are worse in this part of the country," said Dr. Jamary Oliveira Filho, a Harvard-trained neurologist who is studying the Zika outbreak. "It's the perfect setup for epidemic to occur, where there's already inadequate social conditions."
In their study, researchers from Oswaldo Cruz Foundation mention additional theories. One is that co-infection with dengue or chikungunya, two other viruses passed by the same mosquito that carries Zika, might be contributing to the devastating consequences of the virus. Another is that a drought, malnutrition and contamination of drinking water might be a contributing factor.
"The concentration of neuropathies in the northeast states remains a mystery for researchers and health surveillance services," said the researchers. "New detection tools for outbreaks should be pursued to identify real trends and, at the same time, minimize false alarms and panic that could be provoked in populations potentially affected by the Zika epidemic."