Six people out of 5,000 who attended an indoor trial concert last month in Barcelona reported testing positive for COVID-19 afterwards, organisers said on Tuesday, giving hope for the revival of the live music industry.

Ahead of the show, everyone underwent mass screening and antigen tests. There were no mass tests afterwards, but 15 days later only six people reported testing positive for COVID-19 according to public medical records of the participants.

"There is no sign that suggests transmission took place during the event," Josep Maria Llibre, an infectious diseases specialist from the Germans Trias i Pujol hospital told a news conference exactly a month after the March 27 concert.

"We can say that it was not a super-spreading event," he added.

Organised by the hospital and a group of Spanish music promoters, the concert in the Palau de Sant Jordi was billed as Europe's biggest indoor rock concert since the start of the pandemic.

It featured one of Spain's most popular bands, indie rockers Love of Lesbian.

None of the participants had been vaccinated for Covid-19. They wore FPP2 surgical masks at the concert and capacity at bathrooms was limited to avoid crowding but there was no assigned seating or mandatory social distancing.

Out of the six people who later tested positive, "we are certain that in four of these six cases, transmission did not take place during the concert," Llibre said.

Boris Revollo, the virologist involved in the design of the health protocols at the concert, said he could not "categorically" rule out that the other two people were infected during the concert but there was a "very high probability" that they had not.

"The measures which we implemented were very safe," he added.

The Palau can welcome 17,000 people, but only 5,000 ticket holders were allowed in for last month's event.

"With optimised ventilation, antigen tests and the wearing of face masks," we could guarantee a safe space, Libre said.

'Gives us hope'

The deputy mayor of Barcelona, Jaume Collboni, said the results of the study show "it is possible to relax" virus health restrictions and "restart cultural activities".

The same team carried out another test at a smaller concert in December in another Barcelona, the Sala Apolo with an audience of 500 people.

That time around the concertgoers were tested before the show, as well as another 500 people who acted as a control group, and everybody got tested again eight days later.

All of the Apolo concertgoers tested negative while two people in the control group tested positive.

Trial concert or festival events have been held in several European countries, including in Germany and the Netherlands, as part of efforts to allow crowds to form again to see live music.

According to a study published by Spain's Music Federation, the European music industry lost 76 percent of its earnings in 2020 as concerts and major music festivals such as Britain's Glastonbury fell victim to pandemic restrictions.

"The results of the test concert in Barcelona gives us hope, it is a very good thing," Aurelie Hannedouche of France's Union of Contemporary Music (SMA), which represents festivals, concert venues and producers, told AFP.