Case Report and Epidemiological Investigation of Healthcare-associated Plasmodium falciparum Malaria Transmission in Westchester County, New York-2023.

A 65-year-old resident of Westchester County, New York was diagnosed with Plasmodium falciparum infection on 2 October 2023. The case had no recent history of international travel to a malaria-endemic area. An extensive epidemiological investigation was initiated to identify the most likely source of the infection and assess the risk of continuing local transmission. Interviews with the case identified multiple potential exposure routes including domestic travel within the United States, hospitalizations overlapping that of individuals diagnosed with travel-associated malaria, residential proximity to imported malaria cases, and outdoor activity overlapping the potential dusk/dawn biting activity of Anopheles mosquitoes. The epidemiologic investigation included syndromic surveillance, healthcare facility investigations, and genetic analysis of specimens collected from the case patient and other malarious patients with epidemiologic links. Results of the genetic analysis and epidemiologic investigation implicated blood-borne transmission in a healthcare setting from a concurrently hospitalized traveler with confirmed malaria. The mechanism remains unknown, although it was likely due to a lapse in infection control. No mosquito-transmitted cases were identified in New York. No additional induced cases from a blood-borne/healthcare-associated exposure were identified. The identification and prompt investigation of potentially locally acquired malaria infections can aid in preventing additional cases by identifying the source and enacting appropriate control measures if necessary.