Update: Noncongenital Zika Virus Disease Cases — 50 U.S. States and the District of Columbia, 2016

Victoria Hall, DVM; William L. Walker, DVM, PhD; Nicole P. Lindsey, MS; Jennifer A. Lehman; Jonathan Kolsin, MPH; Kimberly Landry, MPH; Ingrid B. Rabe, MBChC; Susan L. Hills, MBBS; Marc Fischer, MD; J. Erin Staples, MD, PhD; Carolyn V. Gould, MD; Stacey W. Martin, MSc


Morbidity and Mortality Weekly Report. 2018;67(9):265-269. 

In This Article

Abstract and Introduction


Zika virus is a flavivirus primarily transmitted to humans by Aedes aegypti mosquitoes.[1] Zika virus infections also have been documented through intrauterine transmission resulting in congenital infection; intrapartum transmission from a viremic mother to her newborn; sexual transmission; blood transfusion; and laboratory exposure.[1–3] Most Zika virus infections are asymptomatic or result in mild clinical illness, characterized by acute onset of fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis; Guillain-Barré syndrome, meningoencephalitis, and severe thrombocytopenia rarely have been associated with Zika virus infection.[1] However, congenital Zika virus infection can result in fetal loss, microcephaly, and other birth defects.[1,2] In 2016, a total of 5,168 noncongenital Zika virus disease cases were reported from U.S. states and the District of Columbia. Most cases (4,897, 95%) were in travelers returning from Zika virus-affected areas. A total of 224 (4%) cases were acquired through presumed local mosquitoborne transmission, and 47 (1%) were acquired by other routes. It is important that providers in the United States continue to test symptomatic patients who live in or recently traveled to areas with ongoing Zika virus transmission or had unprotected sex with someone who lives in or traveled to those areas. All pregnant women and their partners should take measures to prevent Zika virus infection during pregnancy. A list of affected areas and specific recommendations on how to prevent Zika virus infection during pregnancy are available at https://www.cdc.gov/pregnancy/zika/protect-yourself.html.

Before 2015, local transmission of Zika virus had been reported in Africa, Southeast Asia, and the Pacific Islands.[1] In 2015, local mosquitoborne transmission of Zika virus was first identified in Brazil and subsequently spread throughout the Region of the Americas. To date, 48 countries and territories in the Americas have had confirmed mosquitoborne transmission of Zika virus.[4] In the United States, Zika virus disease and congenital Zika virus infection became nationally notifiable conditions in February 2016, when the Council of State and Territorial Epidemiologists (CSTE) approved interim case definitions.[5] In June 2016, CSTE approved revisions to the laboratory criteria and the addition of asymptomatic Zika virus infections to the case definitions.[6] States were asked to reclassify their Zika virus disease cases according to the revised definitions. This report describes confirmed and probable cases of noncongenital Zika virus disease with illness onset during 2016, reported from U.S. states and the District of Columbia to ArboNET, the national arboviral surveillance system. Cases were classified as confirmed or probable according to clinical, epidemiologic, and laboratory-testing criteria. Asymptomatic noncongenital Zika virus infections and all congenital Zika virus infections were excluded from this summary. More information on reported congenital infections is available at https://www.cdc.gov/zika/reporting/pregnancy-outcomes.html.

A total of 5,168 noncongenital Zika virus disease cases with symptom onset during January 1–December 31, 2016, were reported to ArboNET (Figure 1). The number of reported cases peaked in July and declined rapidly after August. Although cases were reported from 49 states and the District of Columbia, approximately half (48%) were reported from three states (Florida [1,107; 21%], New York [1,002; 19%], and California [421; 8%]) (Figure 2).

Figure 1.

Noncongenital Zika virus disease cases (N = 5,168),* by month of illness onset — 50 U.S. states and the District of Columbia, January 1–December 31, 2016
*Other routes include 47 reported cases that were transmitted through sexual contact (45), laboratory exposure (one), and person-to-person through an unknown route (one).

Figure 2.

Number of confirmed and probable Zika virus disease cases, by state of residence — 50 U.S. states and the District of Columbia, January 1–December 31, 2016

The median age of patients with Zika virus disease was 37 years (range = 10 months–89 years), with 4,118 (80%) aged 20–59 years (Table). Overall, 3,310 (64%) cases occurred in females, and a higher proportion of female patients (24%) were aged 20–29 years compared with male patients (16%). Among the 3,310 Zika virus disease cases that occurred in females, 469 (14%) were in pregnant women.

Guillain-Barré syndrome was reported in 15 (0.3%) cases; the median age of these patients was 61 years (range = 27–81 years). Overall, 153 (3%) patients were hospitalized (Table); the median age of hospitalized patients was 41 years (range = 1–89 years). Among the 111 females hospitalized with Zika virus disease, 25 (23%) were pregnant. One hospitalized male patient died.[7]

Among all 5,168 reported cases, 4,897 (95%) occurred in travelers returning from areas with Zika virus transmission (Table). The most common travel destination among the 3,891 (79%) cases for which this information was available was the Caribbean (2,389; 61%), followed by Central America (766; 20%), North America (521; 13%), South America (195; 5%), and Southeast Asia and the Pacific Islands (20; <1%).

Presumed local mosquitoborne transmission was the source of infection for 224 (4%) Zika virus disease patients, including 218 in Florida and six in Texas (Figure 1). The first autochthonous, mosquitoborne cases in the continental United States occurred in Florida in June 2016; local transmission peaked in August and then sharply declined. The patients with locally transmitted disease in Texas all had reported onset in November and December. The median age of patients with local mosquitoborne disease was 37 years (range = 7–81 years) and 103 (46%) were female.

Forty-seven (1%) cases were acquired through other routes, including sexual transmission (45), laboratory transmission (one), and person-to-person through an unknown route (one) (Table). The median age of patients with reported sexually transmitted Zika virus disease was 29 years (range = 18–61 years) and 43 (96%) were female.