During January 22-March 23, 2018, a local health department in Washington was notified of two patients who received a diagnosis of acute hepatitis C virus (HCV) infection. Neither patient had behavioral risk factors associated with HCV acquisition; however, both had received injectable narcotic (opioid) drugs from the same nurse during separate visits to an emergency department (ED) at a local hospital on December 6 and December 16, 2017. Investigation revealed that the nurse had accessed the automated drug dispensing system at a higher frequency than had other staff members, admitted diverting* patients' injectable narcotic and antihistamine drugs for personal use, and tested positive for HCV antibodies (anti-HCV) on March 19, 2018, but did not have quantifiable HCV RNA. Specimens from both patients were sent to CDC for genetic testing, and HCV viral variants analysis found a significant level of genetically similar HCV variants in both patients, indicating a common source of infection. Further investigation was conducted to confirm the infection source, identify other potentially exposed patients, and treat any new patients who received an HCV diagnosis. Monitoring frequency of access to drug dispensing systems can help identify staff members with abnormal dispensing patterns, including diversion activities (1). U.S. health care facilities are required to prevent, identify, and report any loss, diversion, or theft of controlled substances (2).