Health authorities are one step closer to solving Victoria’s SARS-CoV-2 Delta variant outbreak after a breakthrough in genomic sequencing identified an overseas traveller as the index case.

The source of the West Melbourne cluster had evaded the state’s contact tracers, but the possibility that it had escaped from the quarantine hotel system firmed up as the most likely explanation in recent days.

This has now been confirmed, with genomic sequencing finding a match with samples collected from a man in his 40s who returned from Sri Lanka last month, health authorities said.

The index case was identified after scientists at the Peter Doherty Institute for Infection and Immunity in Melbourne retested several swab samples that had previously failed quality-control checks.