Update: Ongoing Zika Virus Transmission - Puerto Rico, November 1, 2015-July 7, 2016.

What is already known about this topic? Zika virus transmission in Puerto Rico has been increasing since it was first detected in November 2015. Zika virus infection is a cause of microcephaly and other severe birth defects and has been associated with Guillain-Barre syndrome and severe thrombocytopenia. What is added by this report? During November 1, 2015-July 7, 2016, specimens from 16,522 patients with suspected Zika virus disease in Puerto Rico were evaluated and 5,351 (32%) had laboratory evidence of current or recent Zika virus infection. The percentage of persons with confirmed or presumptive Zika virus infection among symptomatic pregnant females increased from 8% in February 2016 to 41% in June 2016; during the same time, the percentage of persons with confirmed or presumptive Zika virus infection among symptomatic males and nonpregnant females increased from 14% to 64%. The public health response includes increased surveillance for Zika virus infection, preventing infection in pregnant women, monitoring infected pregnant women and their fetuses for adverse outcomes, controlling mosquitoes, assuring the safety of blood products, and expanding access to the full range of voluntary contraceptive options for women and men. What are the implications for public health practice? The Zika virus outbreak in Puerto Rico continues to expand in geographic extent and number of infected persons. Residents of and travelers to Puerto Rico should continue to employ mosquito bite avoidance behaviors, take precautions to reduce the risk for sexual transmission, and seek medical care for any acute illness with rash or fever. Intensified vector control measures, including an integrated vector management strategy, are needed to help reduce disease spread. Clinicians who suspect Zika virus disease in patients who reside in or have recently returned from areas with ongoing Zika virus transmission should consider testing for Zika virus and report cases to public health officials.