Around July 4, a patient entered an emergency room in Miami-Dade County with a fever, a rash and joint pain — three of the four classic symptoms of the Zika virus. By this point, there had already been about 1,600 other Zika cases in the continental United States, but it soon became clear that this one was different.

All the other patients had either traveled to Latin America or the Caribbean, where Zika had been raging for months — or they had sex or close contact with someone who had been there. Not this patient.

It was the case public health officials had been expecting and dreading: A person in the continental United States had been infected from the bite of a local mosquito.

It would turn out to be the first of a wave of cases health officials are now scrambling to identify and contain. They are investigating 17 suspected cases of locally transmitted Zika — including 13 linked to a an area with a radius of 500 feet that touches two neighboring businesses in the Wynwood section of Miami.