BACKGROUND: In July 2016, the Utah Department of Health was notified of a Zika case (A1) that had no known risk factors for Zika virus (travel to an area with ongoing Zika virus transmission, sexual contact with a person who recently traveled, blood transfusion, or organ transplant). The Zika case had provided care to a 73- year-old man (Index Case) who had recently passed away with an extremely high Zika viremia.
METHODS: Federal, state, and local health departments partnered with the hospital and mosquito abatement districts to assess the potential for person-to-person and/or vector transmission. Family contacts of the Index Case were interviewed to identify symptoms and opportunities for exposure. All family contacts were asked to submit specimens for testing. Heathcare workers that cared for the Index Case were given a questionnaire to assess patient care activities; those with direct contact submitted serum samples for testing. 111 healthcare workers that were not exposed to the Index Case submitted serum samples as controls. Lapses in infection prevention practices were assessed. A community serosurvey was conducted within a 200 meter radius of where the Index Case had resided before being hospitalized. Residents were asked about symptoms and exposure to mosquitoes; they were also asked to provide specimens for testing. Local and federal mosquito abatement teams placed traps at the three residences where A1 and the Index Case resided in order to identify, pool, and test the mosquitoes for Zika virus.
RESULTS: Out of the 19 family contacts that were interviewed and tested, no other family contacts tested positive for Zika virus. A total of 132 potentially exposed healthcare workers were identified; 98 were interviewed and 86 provided a blood specimen for testing. All healthcare workers and controls tested negative for Zika virus. A total of 238 households were approached in the community serosurvey, and 37% of households had at least one family member submit a specimen. All of the 123 individuals that submitted specimens tested negative for Zika virus. Active vector surveillance revealed no invasive Aedes species mosquitoes. All 5,875 mosquito specimens trapped as part of this investigation tested negative for Zika virus by RT-PCR.
CONCLUSIONS: This investigation was the first in the U.S. designed to identify transmission of Zika virus to a person with no known risk factors. Although the mode of transmission is still unknown, the findings suggest that A1 was infected by a rare person-to-person transmission event.