On August 15, 2016, the Mayor's Office of Drug Control Policy in Huntington, West Virginia, notified the Cabell-Huntington Health Department (CHHD) of multiple calls regarding opioid overdose received by the emergency medical system (EMS) during 3 p.m.-8 p.m. that day. A public health investigation and response conducted by the West Virginia Bureau for Public Health (BPH) and CHHD identified 20 opioid overdose cases within a 53-hour period in Cabell County; all cases included emergency department (ED) encounters. EMS personnel, other first responders, and ED providers administered the opioid antidote naloxone to 16 (80%) patients, six of whom were administered multiple doses, suggesting exposure to a highly potent opioid. No patients received referral for recovery support services. In addition to the public health investigation, a public safety investigation was conducted; comprehensive opioid toxicology testing of clinical specimens identified the synthetic opioid fentanyl* and novel fentanyl analogs, including carfentanil,† which had been used by patients who overdosed in Huntington. Results of these two investigations highlight the importance of collaboration between public health and public safety agencies to provide in-depth surveillance data from opioid overdose outbreaks that involve high-potency fentanyl analogs. These data facilitated a public health response through increased awareness of powerful opioid substances requiring multiple naloxone doses for reversal, and improved patient linkage to recovery support services and a harm reduction program from the ED after opioid overdose.