P-1318. Epidemiology and Trends of <i>Corynebacterium diphtheriae</i> in the United States, 2016-2023

Abstract Background Diphtheria, commonly resulting in severe respiratory or cutaneous disease, is caused by toxin-producing (i.e., toxigenic) strains of Corynebacterium diphtheriae. Non-toxigenic C. diphtheriae also cause disease, which is typically less severe but can be invasive. Non-toxigenic bacteria can acquire and express the toxin (tox) gene, providing a mechanism for diphtheria re-introduction to the United States (US). We examine the epidemiology, toxigenicity, and trends of C. diphtheriae isolates submitted to CDC from January 2016 to September 2023. Corynebacterium Diphtheriae Isolates in the United States, by year Methods C. diphtheriae isolates submitted to CDC were cultured and tested by polymerase chain reaction for species confirmation and tox detection; toxin production was confirmed by Elek. Laboratory data were linked with epidemiological case data. Isolates were classified as non-toxigenic if they were tox-negative or toxigenic if tox-positive and Elek-positive. We examined temporal trends in reported isolates and describe demographic and epidemiologic case characteristics. Results A total of 1010 C. diphtheriae isolates were identified during 2016—2023; 99.0% (n=1000) were non-toxigenic, and 1.0% (n=10) were toxigenic. An annual average of 65 (range: 39-95) isolates were reported during 2016—2021; in 2022 and 2023 this increased to an average of 311 (range: 283-338) isolates reported per year. Median patient age was 43 years (range: &amp;lt; 1-98), and 69.0% (n=697) were male. Isolates were primarily obtained from cutaneous (n=689, 68.2%), respiratory (n=133, 13.2%) and blood (n=127, 12.6%) sources. Among non-toxigenic cases with epidemiological data (n=800), major risk factors included housing instability (28.2%) and history of IVDU (20.9%). Eight of the 10 toxigenic cases reported recent international travel to a diphtheria-endemic country. Conclusion There has been an increase in C. diphtheriae isolates identified in the US; however, the majority of isolates were non-toxigenic and from cutaneous sites. Though toxigenic cases were infrequent, risk factors appear to differ between toxigenic compared with non-toxigenic cases. Awareness of case risk factors may help to effectively guide public health intervention and infection prevention and control measures prior to toxigenicity confirmation. Disclosures All Authors: No reported disclosures