BACKGROUND: During 2016, CDPH developed and implemented plans to respond to the growing concern of Zika virus. Zika is transmitted primarily by infected Aedes species mosquitoes; CDPH implemented Aedes surveillance for the first time in 2016. Travel-associated cases are of greater concern in Chicago, which is home to many international travelers, including immigrants from areas with active Zika virus transmission. We reviewed laboratory testing, census, and vector data to evaluate our surveillance and outreach efforts.
METHODS: CDPH established a dedicated Zika call line and email address; developed webinars and educational materials for health care providers; and launched a bilingual public education campaign featured on public transportation, billboards, and at our airports. CDPH facilitated and approved providers’ requests for diagnostic laboratory testing, based on Centers for Disease Control and Prevention guidelines, and performed maternal and child health monitoring. Spatial distribution of test requests by residential location was compared to the distribution of Chicago residents native to areas with ongoing Zika virus transmission, as estimated by the U.S. Census Bureau’s American Community Survey (2010-2014). Vector control staff deployed four BG-Sentinel traps in a total of 9 locations throughout the summer.
RESULTS: During 2016, CDPH received 1736 requests for Zika public health laboratory testing and approved tests for 1444 (83%) individuals, 1182 (82%) of whom were Chicago residents. Among Chicago residents authorized for testing, 209 (18%) were symptomatic, and 1023 (87%) were pregnant women. Thirty-four individuals (2.9%) had evidence of Zika virus infection, of whom 20 (59%) were female, and 6 (18%) were pregnant. Census data showed that immigrants from countries with ongoing Zika transmission were concentrated on the West and Northwest sides of Chicago, while residents tested clustered around the central and near-North sides of Chicago, areas that are more affluent. A total of 4492 Aedes albopictus (81% females) were collected around a single tire recycling facility; targeted response included larviciding, adulticiding, and tire removal.
CONCLUSIONS: Nearly 90% of Chicago residents tested for Zika at public health laboratories were pregnant women, indicating that efforts to target testing were successful. However, tests tended to cluster around more affluent areas of Chicago and were sparse in areas with large immigrant populations, where individuals at high risk for infection may live. Prospectively, we plan to expand public and provider outreach in these communities. The first year of Aedes surveillance in Chicago identified the vector and highlighted the effectiveness of targeted control.