Background:
Passive exposure to electronic cigarette aerosol, which contains various toxic chemicals, has potential adverse health effects in non users. The aim of this study was to quantify such passive exposure in different European countries.

Methods:
Within the TackSHS project, we are conducting a face-to-face cross-sectional study on adults in 12 strategically selected European countries (i.e., Bulgaria, England, France, Germany, Greece, Ireland, Italy, Latvia, Poland, Portugal, Romania, and Spain). The survey includes a specific section on electronic cigarette use and passive exposure to its aerosol. The fieldwork has already been conducted in Italy on a sample of 1059 individuals, representative of the population aged ≥15 years (52.4 million).

Results:
Overall, 1.1% of our Italian population were current electronic cigarette users. Among non-users, 13.7% have been daily exposed to electronic cigarettes in various indoor settings, with a median exposure time around 1 hour and half/day. The proportion of non-users who observed (the last time over the previous 6 months) people using electronic cigarettes was 25% in bars, 20% in restaurants, 18% in disco clubs, 21% in indoor train/metro stations, 20% in airports, 13% in private vehicles (7% in presence of a minor). It was frequent to observe people vaping in several outdoor settings, including restaurant or bar patios (43%), outdoor areas of hospitals (41%) and schools (33%), children's playgrounds (28%), and also while driving motorbikes/scooters (21%), in violation of the traffic laws.

Conclusions:
Current use of electronic cigarette is still relatively low in Italy, but passive exposure to its aerosol is far to be negligible. Our data suggest that, in indoor settings, more than 7 million Italians are daily exposed to the aerosol exhaled by less than 600 thousand electronic cigarette users. Data from other 11 European countries on the issue will allow cross-country comparisons.