Travel-Associated Zika Virus Disease Cases Among U.S. Residents — United States, January 2015–February 2016

Zika virus is an emerging mosquito-borne flavivirus. Recent outbreaks of Zika virus disease in the Pacific Islands and the Region of the Americas have identified new modes of transmission and clinical manifestations, including adverse pregnancy outcomes. However, data on the epidemiology and clinical findings of laboratory-confirmed Zika virus disease remain limited. During January 1, 2015–February 26, 2016, a total of 116 residents of 33 U.S. states and the District of Columbia had laboratory evidence of recent Zika virus infection based on testing performed at CDC. Cases include one congenital infection and 115 persons who reported recent travel to areas with active Zika virus transmission (n = 110) or sexual contact with such a traveler (n = 5). All 115 patients had clinical illness, with the most common signs and symptoms being rash (98%; n = 113), fever (82%; 94), and arthralgia (66%; 76). Health care providers should educate patients, particularly pregnant women, about the risks for, and measures to prevent, infection with Zika virus and other mosquito-borne viruses. Zika virus disease should be considered in patients with acute onset of fever, rash, arthralgia, or conjunctivitis, who traveled to areas with ongoing Zika virus transmission (http://www.cdc.gov/zika/geo/index.html) or who had unprotected sex with a person who traveled to one of those areas and developed compatible symptoms within 2 weeks of returning.

Zika virus is primarily transmitted to humans by Aedes aegypti mosquitoes (1). Most infections are asymptomatic (2). When occurring, clinical illness is generally mild and characterized by acute onset of fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis. Symptoms usually last from several days to a week. Severe disease requiring hospitalization is uncommon, and deaths are rare.

In addition to mosquito-borne transmission, Zika virus infections have been reported through intrauterine transmission resulting in congenital infection, intrapartum transmission from a viremic mother to her newborn, sexual transmission, and laboratory exposure (3,4). Increasing evidence suggests that Zika virus infection during pregnancy can result in microcephaly, other congenital anomalies, and fetal losses (5). Guillain-Barré syndrome also has been associated with recent Zika virus disease (6). However, the frequency of these outcomes is not known. To characterize Zika virus disease among U.S. residents, CDC reviewed demographics, exposures, and reported symptoms of patients with laboratory-evidence of recent Zika virus infection in the United States.

Zika virus disease cases among residents of U.S. states with specimens tested at CDC’s Arboviral Diseases Branch during January 1, 2015–February 26, 2016 were identified. The cases included in this report had laboratory evidence of Zika virus infection based on the following findings in serum: 1) Zika virus RNA detected by reverse transcription-polymerase chain reaction (RT-PCR); 2) anti-Zika virus immunoglobulin M (IgM) antibodies detected by enzyme-linked immunosorbent assay (ELISA) with ≥4-fold higher neutralizing antibody titers against Zika virus compared with neutralizing antibody titers against dengue virus; or 3) anti-Zika virus IgM antibodies with <4-fold difference in neutralizing antibody titers between Zika and dengue viruses and a direct epidemiologic link to a person with laboratory evidence of recent Zika virus infection (i.e., vertical transmission from mother to baby or sexual contact). State and local health departments collected information on patient demographics, dates of travel, and clinical signs and symptoms.

During January 1, 2015–February 26, 2016, a total of 116 residents of 33 states and the District of Columbia with laboratory evidence of recent Zika virus infection were identified on the basis of testing at CDC. One case occurred in a full-term infant born with severe congenital microcephaly, whose mother had Zika virus disease in Brazil during the first trimester of pregnancy (5). Among the remaining 115 patients (including the infant’s mother), 24 (21%) had illness onset in 2015 and 91 (79%) in 2016. Seventy-five (65%) cases occurred in females (Table 1). The median age of patients was 38 years (range = 3–81 years); 11 (10%) cases occurred in children and adolescents aged <18 years. Of the 115 patients, 110 (96%) reported recent travel to areas of active Zika virus transmission and five (4%) did not travel but reported sexual contact with a traveler who had symptomatic illness. The most frequently reported countries with active Zika virus transmission visited by patients were Haiti (n = 27), El Salvador (16), Colombia (11), Honduras (11), and Guatemala (10).

All 115 patients reported a clinical illness with onset during March 2015–February 2016 (Figure). The most commonly reported signs and symptoms were rash (98%), fever (82%), arthralgia (66%), headache (57%), myalgia (55%), and conjunctivitis (37%) (Table 2). Among all 115 patients, 110 (96%) reported two or more of the following symptoms: rash, fever, arthralgia, and conjunctivitis; 75 (65%) reported three or more of these signs or symptoms. Four (3%) patients were hospitalized; no deaths occurred. Among the 109 travelers who had known travel dates, patients reported becoming ill a median of 1 day after returning home (range = 37 days before return to 11 days after return).

Laboratory evidence of Zika virus infection included positive RT-PCR test results in 28 (24%) cases and positive serologic test results in 87 (76%) cases; two (2%) cases had serologic evidence of a recent unspecified flavivirus infection and were classified as Zika virus disease cases based on their epidemiologic link to a confirmed case (one vertical transmission and one sexual contact).

Acknowledgments

State and local health departments.

Corresponding author: Marc Fischer for The Zika Virus Response Epidemiology and Laboratory Team, mfischer@cdc.gov, 970-221-6489.

¹Epidemic Intelligence Service, CDC. (Paige Armstrong and Morgan Hennessey contributed equally to this report).

References

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TABLE 1. Characteristics of 115 residents of U.S. states and the District of Columbia with laboratory evidence of Zika virus disease — January 1, 2015–February 26, 2016*^,†

* Testing performed at CDC’s Arboviral Diseases Branch laboratory.
^† Excludes one infant born with severe congenital microcephaly after maternal infection in Brazil during the first trimester of pregnancy.
^§ Sexual contacts of travelers.

FIGURE. Month of illness onset for 115 patients with laboratory evidence of Zika virus infection among residents of U.S. states and the District of Columbia — January 1, 2015–February 26, 2016*

*Testing performed at CDC’s Arboviral Diseases Branch laboratory.

TABLE 2. Clinical signs and symptoms reported by 115 residents of U.S. states and the District of Columbia with laboratory evidence of Zika virus disease — January 1, 2015–February 26, 2016*

* Testing performed at CDC’s Arboviral Diseases Branch laboratory.
^† Some patients had more than one sign and/or symptom.

The Zika Virus Response Epidemiology and Laboratory Team

Jane Basile, Jacob Brandvold, Amanda Calvert, Amanda Cohn, Marc Fischer, Benjamin Goldman-Israelow, Dana Goodenough, Christin Goodman, Susan Hills, Olga Kosoy, Amy Lambert, Robert Lanciotti, Janeen Laven, Jeremy Ledermann, Jennifer Lehman, Nicole Lindsey, Paul Mead, Eric Mossel, Christina Nelson, Megin Nichols, Daniel O’Leary, Amanda Panella, Ann Powers, Ingrid Rabe, Sarah Reagan-Steiner, J. Erin Staples, and Jason Velez (all these individuals meet authorship criteria).