No new coronavirus cases have been found in New South Wales, after an infected hotel quarantine security guard broke the state's 55 day virus-free streak.
But Gladys Berejiklian admitted health authorities may never determine how the Sofitel Hotel security guard caught the virus.
Genomic testing showed the man, who worked at the Sydney hotel on March 6, had the same highly-contagious UK strain of the virus as a returned traveller at the hotel.
His infection was announced on Sunday and included in Monday's reporting figures, the first to be acquired locally in the state for nearly two months.
But since then, all his household have tested negative and the guard himself remains asymptomatic.