Zika virus is a flavivirus transmitted primarily by Aedes species mosquitoes, 
and symptoms of infection can include rash, fever, arthralgia, and 
conjunctivitis (1).* Zika virus infection during pregnancy is a cause of 
microcephaly and other severe brain defects (2). Infection has also been 
associated with Guillain-Barré syndrome (3). In December 2015, Puerto Rico 
became the first U.S. jurisdiction to report local transmission of Zika virus, 
with the index patient reporting symptom onset on November 23, 2015 (4). This 
report provides an update to the epidemiology of and public health response to 
ongoing Zika virus transmission in Puerto Rico. During November 1, 2015-April 
14, 2016, a total of 6,157 specimens from suspected Zika virus-infected patients 
were evaluated by the Puerto Rico Department of Health (PRDH) and CDC Dengue 
Branch (which is located in San Juan, Puerto Rico), and 683 (11%) had laboratory 
evidence of current or recent Zika virus infection by one or more tests: reverse 
transcription-polymerase chain reaction (RT-PCR) or immunoglobulin M (IgM) 
enzyme-linked immunosorbent assay (ELISA). Zika virus-infected patients resided 
in 50 (64%) of 78 municipalities in Puerto Rico. Median age was 34 years 
(range = 35 days-89 years). The most frequently reported signs and symptoms were 
rash (74%), myalgia (68%), headache (63%), fever (63%), and arthralgia (63%). 
There were 65 (10%) symptomatic pregnant women who tested positive by RT-PCR or 
IgM ELISA. A total of 17 (2%) patients required hospitalization, including 5 
(1%) patients with suspected Guillain-Barré syndrome. One (<1%) patient died 
after developing severe thrombocytopenia. The public health response to the 
outbreak has included increased laboratory capacity to test for Zika virus 
infection (including blood donor screening), implementation of enhanced 
surveillance systems, and prevention activities focused on pregnant women. 
Vector control activities include indoor and outdoor residual spraying and 
reduction of mosquito breeding environments focused around pregnant women's 
homes. Residents of and travelers to Puerto Rico should continue to employ 
mosquito bite avoidance behaviors, take precautions to reduce the risk for 
sexual transmission (5), and seek medical care for any acute illness with rash 
or fever.