Florida Zika Outbreak: Why More Cases Don't Mean the Outbreak is Growing

— -- Since a local outbreak of Zika virus was reported in Florida last month, health officials have been going door-to-door to test residents, spraying to control infected mosquitoes and trying to alert the public about the possibility of mosquito infection.

Yet, the number of cases has continued to increase. Yesterday three new cases were reported in Florida, bringing the total number of people infected during the outbreak to 30.

Though this may look concerning at first, experts say increasing numbers do not necessarily mean the outbreak is getting worse. It could be a sign that health officials are doing what they should to stop the outbreak. Their first priority is to find those infected.

"It’s paradoxical. The reasons we’re finding other cases is that the system is working very well," Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center told ABC News. "Expectations have to be tempered with the reality -- namely this is both a mosquito borne virus and a sexually transmitted virus."

Schaffner said since 80 percent of people with Zika don't have symptoms, that can prolong the time it takes to identify new cases -- especially as more people request testing from their doctors or are tested by health department officials canvassing neighborhoods.

Schaffner also said it's key for the health department to alter their approach if needed. The decision by Florida officials to conduct aerial insecticide spraying shows how they were able to change mosquito control tactics when the Aedes aegypti mosquito proved hard to kill, for instance.

At this point, the Florida Health Department has tested more than 3,300 people statewide since late last year when the Zika virus outbreak in South America first raised alarm. At least 440 people have been diagnosed with travel-related Zika and another 30 contracted the virus locally during this outbreak. Officials believe all active transmission of the virus is still limited to the same less-than-one-square-mile area of northern Miami called Wynwood. The area is home to many restaurants and businesses.

"We cannot expect that we can run in and flip a switch and say 'Oh, OK the outbreak is over,'" Schaffner said, acknowledging the challenges of the Florida health department.

Health officials will likely look at Dengue fever for a framework for how long the Zika outbreak could last, Dr. Stephen Morse, a profesor of Epidemiology at the Columbia University Mailman School of Public Health told ABC News. The Dengue fever virus is in the same family of viruses as the Zika virus and spread by the same mosquito, although it causes different symptoms and is not sexually transmitted.

"If Dengue is any indication it will wind down in a few weeks to months," said Morse, emphasizing that researchers are still learning about the Zika virus every day.

The current outbreak will give more insight about how to fight future outbreaks, he said, especially how to best reach out to community members and how to control the Aedes aegypti mosquito with pesticide.