Some 56 pregnant New York City women have reportedly contracted the Zika virus, bringing the total number in the city with the illness to 530, further fuelling health experts' fears of a devastating toll across the globe.
The growing instances of Zika are all from travel to affected countries or sexual transmission, according to the latest report from the city's Department of Health. None of the illnesses has been tracked to local mosquitoes though officials are boosting bug control in a bid to ward off that possibility.
The growing number, particularly burgeoning instances of locally transmitted cases in Singapore and Haiti, are concerning researchers.
The number of people in Singapore with the illness from mosquitoes in the city-state has spiked from 41 to 115 in just days, despite wide-spread, thorough efforts to control the mosquito population there.
It has been added to the list of places that pregnant women should avoid to dodge the risk of having a baby with microcephaly.
"Any time there is a disease outbreak in Singapore, it tells us how difficult that disease is to control," said Dr. Tom Frieden, director of the US Centers for Disease Control.
Singapore not only has strict mosquito-control measures, but has made Zika a "notifiable" disease, meaning any doctor who diagnoses a Zika case must inform the government, reports NBC News.
Experts in Haiti say there have been 11 births of microcephalic babies or those with the twisted limbs associated with birth to a mother carrying Zika, though only five of those cases have been officially linked to Zika.
Experts fear the devastating disease is a "sleeping giant" in the island nation filled a poorly controlled mosquito population, and wracked by poverty where people have reduced access to good health care, reports NPR.
On another front, meanwhile, scientists are discovering that that disease may not be so benign as once thought for people who are not pregnant.
In seven countries that recently experienced Zika outbreaks, there were also sharp increases in the numbers of people suffering from a form of temporary paralysis called Guillain-Barré syndrome, according to an analysis in the New England Journal of Medicine.
"It's pretty obvious that in all seven sites there is a clear relationship," said Dr. Marcos A. Espinal, the study's lead author and the director of communicable diseases at the Pan American Health Organization.