(Reuters) - European shares retreated from recent gains on Wednesday as concerns over the virus outbreak in China persisted, while markets also waited for service-sector activity data from the bloc.The pan-European STOXX 600 index fell 0.2% by 0803 GMT, having recently recovered from a week of heavy selling as investors gauged the economic fallout from the fast-spreading coronavirus.The focus now turns to the January reading for IHS Markit's services purchasing managers' index, which is..