Evaluating the public health response to a mass bat exposure-Wyoming, 2017.

Mass bat exposures (MBEs) occur when multiple people are exposed to a bat or a bat colony, often over an extended period. In August 2017, a public health investigation was started in response to an MBE that occurred during May-August 2017 at a national park research station in Wyoming. We identified 176 people who had slept primarily in two lodges (Lodges A and B) at the research station, and successfully contacted 165 (93.8%) of these individuals. Risk assessments (RAs) were administered to all 165 individuals to determine degree and type of exposures to bats (e.g., biting or scratching). Exposure status for research station guests was classified as "non-exposed," "low risk" or "high risk," and counselling was provided to guide post-exposure prophylaxis (PEP) recommendations. Prior to public health notification and intervention, 19 persons made the decision to pursue PEP. The healthcare-seeking behaviours of this group were taken to represent outcomes in the absence of public health intervention. (These persons received a RA, and their risk classification was retrospectively assigned.) Approximately 1-2 weeks after conducting the RAs, we conducted a follow-up survey to determine whether recommendations regarding PEP were ultimately followed. The proportion of individuals that unnecessarily pursued PEP was higher among the 19 individuals that sought health care prior to receiving the RA (p < 0.00001). Among those receiving the RA first, all persons classified as high risk followed public health guidance to seek PEP treatment. Despite this, upon re-interview, only 21/79 (26.6%) of guests could accurately recall their risk classification, with most people (55.7%) overestimating their risk. Study findings demonstrate that early public health interventions such as RAs can reduce unnecessary use of PEP and that messaging used during rabies counselling should be clear.