Zika in the United States
The US experienced local Zika transmission in Florida in 2016 and a major epidemic in Puerto Rico — raising alarm about the virus's reach into the Western Hemisphere.
Key Data
| Metric | Data |
| Travel-associated cases 2016 | >5,000 (continental US) |
| Local transmission (continental) | 224 cases (Florida + Texas, 2016-2017) |
| Puerto Rico cases | >36,000 (2015–2016) |
| Sexual transmission cases | ~50 confirmed in continental US |
| First local mainland case | Wynwood, Miami, July 29, 2016 |
| Response authority | CDC, state health departments (Florida, Texas) |
The Florida Local Transmission Crisis
On July 29, 2016, the Florida Department of Health confirmed the first locally acquired Zika cases in the continental United States, in the Wynwood arts neighborhood of Miami. CDC issued an unprecedented travel advisory warning pregnant women to avoid the Wynwood area — the first time such an advisory was issued for a US neighborhood. Intensive mosquito control (aerial spraying, larviciding, targeted elimination of breeding sites) was deployed by Miami-Dade County and Florida. A second cluster emerged in Miami Beach in September 2016. All local Florida transmission was declared over in December 2016 after 218 locally acquired cases.
Puerto Rico: America's Epicenter
Puerto Rico, a US territory, experienced the Americas' largest per-capita Zika epidemic. With year-round Aedes aegypti presence and a warm climate, Puerto Rico reported over 36,000 cases in 2015-2016. CDC coordinated a major response including free mosquito repellent distribution, expanded prenatal Zika testing, and surveillance of pregnant women. Puerto Rico's epidemic included congenital Zika syndrome cases and highlighted the particular vulnerability of US territories without the same healthcare resources as the continental US. Blood supply safety was a concern — all blood donations from Puerto Rico were screened for Zika during the epidemic.
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FAQ
A future local Zika transmission event in Florida is possible. Aedes aegypti mosquitoes remain established in southern Florida, and Zika continues to circulate in the Caribbean and Latin America. If an infected traveler returns and is bitten by local Aedes mosquitoes who then bite other people, local transmission could occur again. Florida maintains enhanced Zika surveillance and rapid response capacity. Climate change expanding Aedes ranges northward increases the geographic area at risk over time.
For most travelers, Zika infection is mild (or asymptomatic in ~80% of cases). The primary concern is for pregnant women or those planning pregnancy. CDC maintains a Zika travel advisory website listing current Zika-risk areas. Travelers to affected regions should use DEET repellent, wear protective clothing, and if pregnant, discuss with their physician whether travel is advisable. Sexual transmission risk persists for weeks to months after returning from affected areas.
Sources: CDC Zika virus disease US cases 2016; Florida Department of Health Zika reports; MMWR Zika local transmission Florida; PAHO Puerto Rico Zika data.
Related: Zika overview · Brazil Zika · Puerto Rico Zika