Party-goers have been criticised by Swansea University Health Board for misleading contact tracers and putting the wider community at risk.
At least six people who attended the party on 10th April in the Derwen Fawr area have tested positive for Covid-19 and a further 13 contacts are undergoing tests.
The health board is urging people not to organise or attend large gatherings indoors or outdoors, and to co-operate fully if contact tracers get in touch.
It comes after efforts to track down everyone connected to the party were thwarted by some attendees who claimed they were not in Swansea at the time and that the party took place elsewhere.
The health board said the occupiers of the house where the gathering took place also denied at first that it happened.
The close timing of four positive Covid-19 cases – two men and two women – hadraised suspicions of an indoor gathering. But efforts by Swansea Test Trace Protectcontact tracers to find out more were frustrated by the misleading information theywere given.
Swansea Council environmental health officials, in partnership with South Wales Police, then investigated and were able to uncover evidence enabling tracers to track attendees and their contacts.
Swansea Bay University Health Board’s Director of Public Health, Dr Keith Reid said: “The misleading information provided by some people, in this case, had a detrimental effect on both the speed of the investigation and the tracers’ ability to identify exactly routes of transmission and protect the public."
He added: “This caused the potential for further spread within the community and placed the wider community at risk."
“We are continuing to monitor the situation for further cases.”
“But the behaviour demonstrated by the individuals, in this case, is extremely disappointing. Not only did their decision to hold a party put others at risk, but they made matters worse by then misleading contact tracers."
“That it needed a concerted investigation by officials to get to the bottom of it is shocking," said Dr Reid.
The party follows earlier reports of indoor social gatherings in the Clase and Briton Ferry areas, which led to a chain of Covid-19 infections.
Although infection rates in Swansea are improving overall, the city remains top of the league table in Wales for confirmed cases.
Dr Reid said: “It is very important that people continue to follow the rules, and remember to still wash their hands, wear face-coverings in indoor public places and keep two-metres distance from people they don’t live with.”
From Saturday 24 April, up to six people from up to six households will be able to meet outside. The total does not include children.