In a single, chaotic day, Houston’s reported 2017 tally of Zika cases appeared to double.

On Thursday, the Centers for Disease Control and Prevention confirmed that six pregnant women in Harris County have tested positive for the mosquito-borne illness, bringing the definitive year-to-date number for Houston-area Zika cases up to 11. It’s unclear at this point if any of these women’s babies will suffer from microcephaly — the birth defect, present in about 5 percent of Zika cases, that causes infants to be born with small heads.

These latest infections were first detected by Legacy Community Health, a nonprofit that provides health care to underserved communities in Texas. Kevin Nix, a spokesman for Legacy, said the cases date from late 2016 until early this year. It took some time for the state and the federal government to confirm the findings, he said.

“I want to make it clear: It wasn’t just like, all of a sudden, there were six,” Nix said. “But all the final confirmations on the tests came back in May.”

So far, all of Houston’s Zika infections — included these six latest incidents — have come from people who traveled to Zika hot spots in Central America, South America or the Caribbean. Nix didn’t specify which countries these six women had visited but stressed the cases were “all travel-related.”

Until Thursday, there were five cases of Zika confirmed in 2017 for Houston, with confirmation dates ranging from January through March, according to the Houston Health Department. One man and four women, all of whom had traveled to Mexico or El Salvador, were found to have the illness.

If these newest cases had been locally transmitted — or if six infections had been discovered all at once — that would have been far more serious, Nix said. He expressed concern that some news reports on the findings, including a Houston Chronicle article Thursday, had been insufficiently clear on these points.

“That's not the case," Nix said of the false impression that these six women had contracted Zika locally. “That would have been a whole other level."

A local Zika transmission — or six of them — would be troubling because it would indicate that Houston mosquitoes are now spreading the disease. That would put all Houstonians, and not simply people who have traveled abroad, at risk.

But the doubling of Houston’s Zika cases has nonetheless ignited fears among residents and created a chaotic scene for Houston’s mosquito control agencies, which are more focused on preventing local infections. Last year, the area around Brownsville and the Rio Grande Valley experienced some of the first locally transmitted Zika cases in the United States. A travel advisory for that region remains in effect.

On Wednesday, the Houston Health Department sent 80 public health workers to the Kashmere Gardens and Fifth Ward neighborhoods of Houston to hand out informational pamphlets, mosquito repellent and condoms to residents. That initiative came after Harris County Public Health “detected an unusually large number of mosquitoes in sections of the neighborhoods,” according to a news release from the health department.

Porfirio Villarreal, a spokesman for the Houston Health Department, said it’s the first time the city has gone door-to-door in an effort to fight Zika.

But does this update make Houston more at-risk for a local Zika outbreak than it was on, say, Tuesday? Not really, according to local Zika experts who spoke to the Houston Press.

Martha Marquez, a spokeswoman for Harris County Public Health, expressed frustration that information-sharing about the new cases had been “not very well coordinated.” But she stressed that her agency has still not found a single Houston-area mosquito that has tested positive for Zika.

“Nonetheless, we continue to recommend that people take precautionary measures,” Marquez said. “Most importantly, do not bring any mosquitoes into your home.”

