Let's trace: Leishmaniasis in Tuscany (Italy), tracking, research, analysis and continuous evaluation - a retrospective study protocol on underreporting of human cases, geolocation and public health implications.

INTRODUCTION: Leishmaniases are a group of vector-borne diseases caused by parasites of the genus Leishmania, which are renowned for increasing global spread due to factors like climate change, globalisation, urbanisation and migration. Leishmaniasis is classified as a neglected tropical disease but is endemic in several areas of the Mediterranean Basin, including Italy, where Leishmania infantum is most involved as the parasite, phlebotomine sand fly as the vector and dog as the principal reservoir. Effective surveillance of communicable infectious diseases is a goal worldwide for organisations such as the WHO and for local and national governments but is an unfulfilled objective. Even in Italy and particularly in the region of Tuscany, despite mandatory reporting, significant gaps each year are identified between reported cases and hospital admissions. By estimating the underreporting of confirmed human leishmaniasis cases, this protocol aims to suggest actions to strengthen the current epidemiological surveillance system to enable timely and effective public health intervention in human and veterinary populations. METHODS AND ANALYSIS: This retrospective multicentre study, conducted in the Central Tuscany Health District, the most populous area of the Tuscany region with approximately 1.6 million inhabitants, is based on the analysis of data collected from 2014 to 2024 using diagnostic laboratory, hospital and regional information system sources. The primary objective is to estimate the degree of underreporting of leishmaniasis in this area through the application of capture-recapture models. The secondary objective is to analyse the clinical and demographic characteristics of individuals diagnosed as confirmed leishmaniasis cases between January 2014 and December 2024, as well as to perform a geolocation analysis of the cases. The study includes the entire population, both adult and paediatric, of the Central Tuscany Health District who underwent laboratory testing for leishmaniasis (serological tests identifying the presence of antibodies; parasitological examination with evidence of amastigotes in aspirates, smears or biopsy sections; culture examination of aspirates, biopsies and/or peripheral blood positive for the presence of promastigotes; identification of Leishmania nucleic acid in aspirates, biopsies and/or peripheral blood samples via molecular diagnosis). ETHICS AND DISSEMINATION: The study is being conducted in accordance with the protocol approved by the Ethics Committee of the Tuscany Region - Pediatrics Section, in November 2024. Ethics Committee opinion register number: 219/2024. Because the study uses only pseudonymised, routinely collected administrative and laboratory data with no direct patient contact or intervention, individual informed consent was not required, as confirmed by the Ethics Committee. Findings will be submitted to a peer-reviewed journal, presented at international conferences and presented at stakeholder workshops.