Ongoing Zika Virus Transmission — Puerto Rico, November 23, 2015–March 11, 2016

BACKGROUND: Zika virus (ZIKV) is transmitted primarily by Aedesmosquitoes. Studies suggest most infected persons are asymptomatic; symptoms include fever, rash, arthralgia, and/or conjunctivitis. In December 2015, the Puerto Rico Department of Health (PRDH) reported the first U.S. locally acquired ZIKV infection, with symptom onset on November 23, 2015.

METHODS: Laboratory-positive cases were defined by detection of ZIKV by reverse transcription-polymerase chain reaction (RT-PCR) or anti-ZIKV immunoglobulin M (IgM) antibody by enzyme-linked immunosorbent assay (ELISA) with dengue virus IgM negative results, depending on time between symptom onset and specimen collection. Data on laboratory-positive cases were abstracted from PRDH Arboviral Surveillance System, and are reported by date of symptom onset.

RESULTS: During November 23, 2015–March 11, 2016, 350 ZIKV laboratory-positive cases were detected out of 2,987 people tested; 311 (89%) were RT-PCR positive and 39 (11%) were ELISA positive. Median age was 36 years (range = <1–89); 226 (65%) were female. Following the index case in November 2015, 9 (3%) cases were reported in December, 52 (15%) in January, 254 (73%) in February, and 34 (10 %) up to March 11. Cases were reported from 44 (56%) of 78 municipalities. Among cases, 40 (11%) were pregnant women, with no adverse pregnancy outcomes reported to date. Six (2%) cases required hospitalization, including three cases of Guillain-Barré syndrome. No deaths or cases of microcephaly were reported.

CONCLUSIONS: Since November 2015, cases of ZIKV have increased, and ongoing transmission is expected to spread ZIKV throughout Puerto Rico. Residents and visitors to Puerto Rico, especially pregnant women, should avoid mosquito bites, including insect repellent use. Possible sexual transmission of ZIKV may be prevented by consistent and correct use of condoms or abstaining from sexual contact.