Background and objective:
Wastewater reuse is a promising alternative source of water supply considering the water scarcity related to climate change. However, if not adequately treated, wastewater represents a source of microbiological health risk. The wastewater reuse in agriculture can promote the production and dispersion of aerosol containing pathogens such as _Legionella_ opening new risk profiles for human health. The purpose of the study was to investigate risks related to _Legionella_ occurrence in wastewater samples reused in agriculture.

Methods:
_Legionella_ (spp. e _pneumophila_) were monitored using both culture and molecular (qPCR) methods in influents (n=21) and effluents (n=21) of 3 wastewater treatment plants (WWTPs) equipped with treatments suitable for wastewater reuse (WWTP1 and WWTP2 with membrane bioreactor-MBR system and WWTP3 with ClO2 disinfection)

Results:
The qPCR revealed_ Legionella_ spp. presence in all samples. _L. pneumophila _was detected in 86% and 57% of the WWTP1 and WWTP2 influents and in all pre-disinfected samples of WWTP3, while only some WWTP3 effluents were contaminated. A significant reduction in _Legionella_ contamination was obtained only with MBR highlighting that this treatment allows to control _Legionella_ contamination. A lower _Legionella_ contamination was observed with culture method respect to molecular one. The significant correlation between _Legionella_ presence and physicochemical characteristics of wastewater (BOD-biochemical oxygen demand, COD-chemical oxygen demand, TSS-total suspended solids) highlights the possibility that these parameters support the risk evaluation of _Legionella_ occurrence in wastewater.

Conclusion:
Results obtained highlight the need to carry out further investigation on _Legionella_ contamination in wastewater samples when the reuse of the effluents in agriculture is purposed. The use of molecular method could allow more precautionary risks estimation. This is particularly important considering that aerosol formation from wastewater contaminated by _Legionella_ could represent an occupational health risk associated with reuse.