Zika in Puerto Rico
Puerto Rico bore the heaviest Zika burden of any US jurisdiction in 2015–2016 — over 36,000 cases, a stretched healthcare system, and urgent pregnancy surveillance mobilized across the island.
Key Data
| Metric | Data |
| Total cases (2015–2016) | >36,000 confirmed and probable |
| Estimated population infected | ~25% (seroprevalence estimates) |
| Pregnant women in registry | >1,000 Zika-positive pregnant women |
| Blood supply action | All PR blood donations screened for Zika |
| CZS cases | Confirmed congenital Zika syndrome cases reported |
| Response lead | Puerto Rico Dept of Health + CDC Emergency Operations |
Scale of the 2015–2016 Epidemic
Puerto Rico detected its first locally acquired Zika case in December 2015, with rapid escalation through 2016. By mid-2016, Puerto Rico was reporting thousands of new cases weekly. CDC deployed over 200 staff to Puerto Rico during the response — one of the largest CDC domestic emergency deployments since Hurricane Katrina. The epidemic was amplified by Puerto Rico's year-round Aedes aegypti presence, warm tropical climate, and the fact that the entire 3.3 million population was immunologically naive to Zika.
The outbreak had unique characteristics for the US: sexual transmission events were tracked, blood supply safety required emergency Zika testing of all island donations (the FDA authorized emergency Zika nucleic acid testing for blood), and free mosquito repellent was distributed to all households through the Puerto Rico Department of Health — an unprecedented public health logistical effort.
Pregnancy Surveillance and Outcomes
Puerto Rico established a comprehensive pregnancy registry for Zika-exposed women, with enhanced prenatal monitoring including serial ultrasound and neonatal follow-up. Over 1,000 Zika-positive pregnant women were enrolled and followed through delivery. The registry documented cases of microcephaly, intracranial calcifications, and other features of congenital Zika syndrome. Puerto Rico's experience contributed substantially to the global understanding of congenital Zika syndrome rates and risk factors. CDC noted that Puerto Rico's experience — unlike Brazil where the microcephaly-Zika link took months to confirm — benefited from regularly updated knowledge of the Zika-CZS link established in Brazil.
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FAQ
The epidemic phase has passed and current Zika transmission in Puerto Rico is at low levels. However, Aedes aegypti is permanently established on the island, and Zika could circulate at any time. For non-pregnant visitors, the practical risk is very low. For pregnant women or those trying to conceive, checking CDC's current Puerto Rico Zika travel notice and consulting a physician before travel remains advisable. Standard mosquito protection (DEET, protective clothing, screened accommodation) significantly reduces risk.
Puerto Rico's Zika burden was dramatically higher than the continental US due to geography and climate: Puerto Rico has year-round tropical temperatures supporting continuous Aedes aegypti breeding, while the continental US has Aedes populations that are seasonal and more geographically limited. Additionally, Puerto Rico's fiscal crisis had strained public health infrastructure, and the island had less mosquito control capacity relative to what was needed. These structural factors made Puerto Rico far more vulnerable to mosquito-borne disease amplification.
Sources: Puerto Rico Dept of Health Zika data; CDC Puerto Rico Zika response reports; MMWR Zika PR pregnancy registry; NEJM (Shapiro-Mendoza et al. Zika CZS Puerto Rico).
Related: Zika overview · USA Zika · Brazil Zika