Zika-related Twitter incidence peaked after the World Health Organization declared an emergency. Five themes were identified from Zika-related Twitter content: (1) societal impact of the outbreak; (2) government, public and private sector, and general public responses to the outbreak; (3) pregnancy and microcephaly: negative health consequences related to pregnant women and babies; (4) transmission routes; and (5) case reports. User-generated contents sites were preferred direct information channels rather than those of the government authorities.