Order of authorship in the original publication: Grubaugh, Ladner, Kraemer. The authors found that the Zika virus was introduced into Florida at least 4 times, but perhaps as many as 40 times, before it was detected, that it entered Florida from the Carribean (probably Puerto Rico) and most likely from cruise ship travel.

Follow-up papers published immediately after this in the same journal issue:

Faria, N.R.; Quick, J., Claro, I. M.; et al. "Establishment and cryptic transmission of Zika virus in Brazil and the Americas," Nature, 546 (2017) 406-410. The authors generated data from a travelling genomics laboratory sequencing Zika virus (ZIKV) genomes around the country. They found that the virus was first detected in Brazil in May 2015, about a year after it was first introducted.

Metsky, Hayden C.; Matranga, Christian B.; Wohl, Shirlee, et al. "Virus evolution and spread in the Americas," Nature, 546 (2017) 411-415. The authors showed the spread of Zika in the Americas using genomes of people and mosquitoes (110 ZIKV genomes from 10 countries), tracing the common ancestor of ZIKV in the Americas to about late 2013 and pinpointing it to the NE/Bahia region of Brazil.

Digital facsimile from PubMedCentral at this link.

(Thanks to Juan Weiss for these references and their interpretation.)