A comparative analysis of the 2007 and 2017 Italian chikungunya outbreaks and implication for public health response

Chikungunya virus (CHIKV) is a mosquito-borne infection that is emerging in temperate areas of Europe, following the expansion of one of its vector species, Aedes albopictus. Although CHIKV fever is a self-limiting disease, with a clinical syndrome often resolving within few days, it can also cause severe sequelae, including chronic polyarthralgia lasting up to 5 years. Additionally, CHIKV outbreaks may limit blood bank donations, adding economic burden on the health system. Public health authorities in Europe need to increase their preparedness against this emerging threat. Two large CHIKV outbreaks occurred in Italy in 2007 and 2017, with hundreds of cases and significant geographical spread. The aim of this paper is to review and compare the 2 Italian outbreaks in terms of available estimates of key epidemiological features, patient clinical presentation, virus and immunological characteristics, and public health response. Recommendations for public health and future directions for research are also discussed and highlighted. Key results Both outbreaks started in small towns, but cases were also detected in nearby larger cities where transmission was limited to small clusters. The time spans between the first and the last symptom onsets were similar between the 2 outbreaks, and the delay from the symptom onset of the index case and the first case notified was considerable. Comparable infection and transmission rates were observed in laboratory. The basic reproductive number (R-0) was estimated in the range of 1.8-6 (2007) and 1.5-2.6 (2017). Clinical characteristics were similar between outbreaks, and no acute complications were reported, though a higher frequency of ocular symptoms, myalgia, and rash was observed in 2017. Very little is known about the immune mediator profile of CHIKV-infected patients during the 2 outbreaks. Regarding public health responses, after the 2007 outbreak, the Italian Ministry of Health developed national guidelines to implement surveillance and good practices to prevent and control autochthonous transmission. However, only a few regional authorities implemented it, and the perception of outbreak risk and knowledge of clinical symptoms and transmission dynamics by general practitioners remained low. Major conclusions Efforts should be devoted to developing suitable procedures for early detection of virus circulation in the population, possibly through the analysis of medical records in near real time. Increasing the awareness of CHIKV of general practitioners and public health officials through tailored education may be effective, especially in small coastal towns where the outbreak risk may be higher. A key element is also the shift of citizen awareness from considering Aedes mosquitoes not only as a nuisance problem but also as a public health one. We advocate the need of strengthening the surveillance and of promoting the active participation of the communities to prevent and contain future outbreaks. Author summary In Europe, vector-borne diseases have been increasing during the last decades. CHIKV is an example of a neglected emerging disease transmitted by the alien mosquitoes Ae. albopictus that caused 2 large outbreaks in Italy in 2007 and 2017. It is important to compare the main epidemiological, clinical, virological, and immunological features, as well as the public health responses, to increase preparedness to face future outbreaks.