Discussion
In this Zika virus outbreak, approximately three
quarters of Yap residents were infected with Zika
virus, and we estimated that more than 900 people
had illness attributable to Zika virus infection.
Zika virus infection was widespread across all geographic
areas of Yap and caused relatively mild
illness lasting several days. There were no deaths
or hospitalizations attributed to Zika virus. We
were unable to detect Zika virus in any mosquito
samples, and therefore we cannot determine with
certainty the vector of transmission. On the basis
of the relative abundance of Aedes hensilli and previous
evidence that this species was the most
likely vector of dengue virus transmission on
Yap, it is plausible that Aedes hensilli was a vector
of Zika virus transmission in this outbreak.21
The clinical signs and symptoms of Zika virus
infection were consistent with those described in
a previous report of one male patient but different
from those described in a previous case series.2,20
In that case series, rash or conjunctivitis
was not reported and arthralgia was noted in only
one of seven patients. Fever was reported in all
seven patients, but the study included only patients
who were hospitalized with febrile illness.19
The detection of Zika virus RNA in the serum
of acutely ill patients and the absence of nucleic
acid of other arboviruses provide convincing evidence
that the outbreak was caused by Zika virus.
Although the transmission of dengue virus is common
in Micronesia, none of the 137 patients for
whom acute-phase specimens were available had
evidence of dengue virus RNA in their serum.