Finally, the time has come… the first documented instance of local transmission in the continental United States has occurred…and Miami Florida is now ground zero.

The state Department of Health has announced that four cases of Zika infection in Miami are highly likely to have been caused by locally infected mosquitoes. The area of active transmission is limited to a one-square mile area just north of downtown Miami. As of yet, no mosquitoes tested have been found to be carrying the Zika virus. The local DPH is going door to door in the neighborhood collecting urine samples to test residents.

Miami-Dade County is one of the biggest ports of entry into the United States from countries where the Zika virus is circulating, and experts have long described it as one of the areas most at risk for the spread of the disease.

The four cases involve three men and one woman. The statement did not indicate if the woman was pregnant. Of the four people infected all are active Zika cases however their illness has no required hospitalization.

Zika, a virus transmitted by mosquitoes or by sex with a person who has been infected by a mosquito, can cause brain damage and neurological disorders in babies born to mothers who contracted it inpregnancy. It has spread through dozens of countries in Latin America, causing hundreds of birth defects among largely poor populations who are ill-equipped to handle them.

The cases mark a new stage in the life of the virus in the United States. There are more than 1,300 Zika cases in the continental United States, but until the Florida announcement, all of them had been a result of travel abroad — contracted either by a mosquito bite elsewhere or by sexual intercourse with someone who had traveled to a Zika-infected area.