To date, all confirmed Zika virus cases in Wisconsin residents are travel-associated, occurring in people who traveled to locations with active Zika virus transmission, had sexual contact with someone who traveled to locations with active Zika virus transmission, or were born to a mother who traveled to locations with active Zika virus transmission during pregnancy.
Wisconsin Department of Health Services (DHS) is conducting surveillance for Zika virus infections by tracking the physician or laboratory-reported cases of Zika virus and by offering fee-exempt testing for qualifying patients.
Below are the 2016 data for confirmed travel-related Zika cases in Wisconsin. For more detailed information on 2016 data see the 2016 Zika Data Brief (PDF).
For current case numbers, view the DHS Zika home page.
Cases reported by...
During 2016, Wisconsin approved the testing of 1,062 individuals of whom 916 (86%) were female and 145 (14%) were male. Of the people tested for Zika virus in Wisconsin in 2016, 68% were pregnant women. Of the 63 total Zika cases confirmed in 2016, 41 (65%) were female and 22 (35%) were male.
The distribution of Zika infections in Wisconsin in 2016 is skewed toward females—65% of cases. This pattern is likely a reflection of the larger number of females tested due to a focus on testing pregnant women. Additionally, when symptoms are present, Zika virus infections often cause only a mild illness. As males would not have pregnancy-related concerns, they may not seek testing at the same rate as females.
Overall, 59% of all Wisconsin cases were confirmed among people ages 15-34. However, people of all ages can become infected with Zika virus. The age distribution of Wisconsin Zika cases likely reflects the demographics of the population tested for Zika virus. Since Zika virus infection during pregnancy can cause serious birth defects, proper diagnosis of Zika virus among residents who are currently pregnant or who are of childbearing age is a priority.
Among confirmed Zika virus cases in Wisconsin in 2016, 54% occurred during July and August. Many Caribbean, Central American, and South American countries experience high levels of mosquito activity throughout these months and were reporting ongoing local Zika transmission during this time period in 2016. Summer in Wisconsin is also a popular time for travel with most schools and universities not in session, and many honeymoon trips following the summer wedding season.
Based on reported exposures, Wisconsin travelers presumably acquired Zika virus from 14 different countries outside of the United States and one additional traveler from Miami, Florida. Some of the Zika virus cases in 2016 reported both travel to a Zika-affected area and sexual contact with a traveler to a Zika-affected area within a similar time period, and thus, the mode of transmission cannot be definitively determined.
One case reported travel to multiple international locations with Zika transmission and is not represented on the map. Another case reported no travel, only sexual contact with a traveler, and thus presumably acquired Zika through sexual transmission. This sexually transmitted case is also not represented on the map.
The number of cases per country reflects travel patterns among Wisconsin residents, and is not necessarily indicative of the level of risk associated with active Zika virus transmission in that country.
The 2016 summary data from Wisconsin travel-associated Zika virus cases do not necessarily reflect the characteristics of the disease observed nationally. However, in looking more closely at our Wisconsin cases, we may be able to identify geographic, temporal, or other epidemiological trends specific to travel-related exposures in Wisconsin residents. This information could be of use in discussions with patients or in designing and implementing outreach and prevention activities.
Due to the nature of Zika virus infections, with about 80% of people infected experiencing no symptoms, the 2016 case count is likely an underrepresentation of the true number of infections among Wisconsin residents.