(Adds details, background) MILAN, May 13 (Reuters) - Italian infrastructure group Atlantia on Thursday reported a net loss in the first quarter and confirmed it would decide on the sale of its 88% stake in motorway unit Autostrade by June 11. The group controlled by Italy’s Benetton family has been under pressure to loosen its grip on Autostrade since a bridge managed by the motorway unit collapsed in the port city of Genoa on Aug. 14, 2018, killing 43 people. Last month the group decided to submit to shareholders on May 31 an offer it received from state lender CDP, Macquarie and Blackstone for the motorway unit. Following the shareholders’ vote, Atlantia will decide whether to accept the bid valuing Autostrade 9.3 billion euros, it said. The group said on Thursday the prolonged impact of the pandemic on motorway and airport traffic was the main reason behind a 67 million euro ($81 million) net loss for the first quarter, down from a 10 million euro loss last year. An expected relaxation in movement restrictions and the roll-out of vaccination campaigns should allow traffic to recover this year reaching 90% of the 2019 level on Atlantia’s motorways. The outlook remained bleak for airports managed by the group, whose 2021 traffic was expected to be only 30% of the 2019 level. The group said its sales fell 8% between January and March to 2.025 billion euros, adding that it confirmed its guidance for 9.4 billion euros in revenue for the full year. Atlantia said in the statement that its units Autostrade and SPEA were notified that the preliminary investigation into the collapse of Genoa bridge had come to an end in April. A trial involving the two units and dozens of its former employees is expected to start before the end of this year, it said. Separately, the Italian market watchdog said banking foundation CRT had increased its stake in Atlantia to 5.5% from 4.8% ahead of a key shareholders’ meeting on May 31. ($1 = 0.8289 euro) Reporting by Francesca Landini; editing by Valentina Za and Jonathan Oatis Our Standards: The Thomson Reuters Trust Principles.