West Nile Morbidity and Mortality in a Mid-Atlantic Health Care System, 2013-2024

West Nile virus (WNV) is transmitted by mosquitoes to humans in many regions and can cause neuroinvasive disease and death. To better understand the local burden of disease caused by WNV and risk factors for disease severity, we analyzed cases from across the Johns Hopkins Health System Corporation. We identified 86 patients who met confirmed/probable case definitions for WNV infection from 2013 to 2024. Seventy-one patients (83%) had West Nile neuroinvasive disease (WNND), and nine (10%) died. Encephalitis (n = 47) was the most common complication and was associated with increased age, alcohol use disorder, immunocompromised status, and a higher Charlson Comorbidity Index. Of the 21 patients in the cohort who were immunocompromised, 20 (95%) developed WNND, and 4 (19%) died. The overall median hospital length of stay was 8 days (interquartile range 5-15). People diagnosed with WNV in this health care system experienced significant morbidity and mortality from WNND, notably when immunocompromised.