Diagnosis of dengue fever in North West Italy in travelers from endemic areas: a retrospective study

Background Domestic outbreaks of Dengue (DENV) fever from imported cases have to be considered a possible risk in non-endemic countries where Dengue vectors are present, such as in Italy. Objective To review imported acute/recent DENV infections in a one-year survey in a North West Italy region where the presence of Aedes albopictus is documented. Study design We retrospectively reviewed laboratory and clinical records of Italian febrile travelers from Dengue endemic areas referring to the local reference Centre for Infectious Disease, covering a population of about 4 million people. Results Acute/recent DENV infection was identified in 15 out of 91 travelers from endemic areas (16.5%) including 12 primary and 3 secondary infections; in 6 patients the virus was detectable in blood according to molecular real-time Polymerase Chain Reaction-based assays: in 9 patients the diagnosis of DENV infection was accomplished by the combination of specific IgM reactivity, high IgG titers, IgG seroconversion from negative to positive and increasing (four-fold) IgG titers in paired serum samples. Two cases of DENV infections were imported from South Egypt in patients travelling together, confirming the importance of returning travelers as sentinels of a rapidly changing epidemiology in specific geographic areas. Conclusions Our findings outline the high rate of imported Dengue infection in North West Italy and emphasize the need for a continued Dengue surveillance in non-endemic countries as well as a careful evaluation and follow-up of febrile patients returning from Dengue endemic countries.