To the Editor

The article by Söbirk S et al. ‘Imported leishmaniasis in Sweden 1993–2016 [Reference Söbirk1],’ affirmed that most cases dating back 20 years were imported. We recently managed a patient aged 12 years who visited the US from the Middle East. He presented to our Emergency Department with chronic rash and ulcer in a lower extremity with reported exposure to pets, and freshwater pools but equivocal exposure to sand-fly. One of our differential diagnoses before referral to a specialist was cutaneous leishmaniasis. While researching the topic we read the article by Söbirk et al. in which authors confirmed the same diagnostic challenges and difficulties as frontline practitioners in Sweden face. It has been postulated that Leishmaniasis infections could pose a potential public health threat because of the high prevalence of asymptomatic parasite carriers [Reference Michel2]; however, leishmaniasis is not a reportable disease and there is no surveillance system in the US or Sweden as both countries are considered non-endemic. Surveillance of leishmaniasis inherently has challenges; different operational and research problems concerning epidemiological surveillance of leishmaniasis have been previously reported [Reference Gradoni3]. Generally, the incidence and distribution depend on the characteristics of the parasite species, the local ecological characteristics of the transmission sites and human behaviour. Animal reservoir hosts (domestic dogs, foxes, gerbils and jackals) also contribute to local incidence. Although the authors acknowledge underreporting, they did not attempt to classify underreporting rates or adjust the incidence rates using multipliers. The use of conservative assumptions for underreporting rates and resultant multipliers has demonstrated that real leishmaniasis incidence rates may be higher [Reference Alvar4]. We acknowledge that this study was a retrospective cohort analysis and not an official surveillance system. Nevertheless, case underreporting affects the characteristics that make a surveillance system robust such as representativeness, sensitivity and positive predictive value and should be carefully considered moving forward [Reference Klaucke5]. In the last four years, data from Sweden showed that most confirmed cases were in individuals below 18 years of age; the only reason provided was that they were mainly immigrants or travellers from a highly endemic country. The presence of any other underlying cause that makes this age group vulnerable was not addressed in the paper. It would be beneficial if authors could discuss the variances in incidence to help readers understand whether there were specific natural or epidemiological factors or whether it was the complex interplay of socio-economic factors, environmental and climate change, zoonotic seroprevalence or unclear causative factors that contribute to the variations in incidence.