Rigorous detective work, hours spent on the phone and a complex maze of contacts and locations have allowed NSW Health to discover “patient zero” of Sydney’s latest outbreak at the Crossroads Hotel in Casula.

NSW Health Operations Manager Jennie Musto – who oversees teams of contact tracers – said the initial outbreak was caused by a man travelling from Melbourne to Sydney at the end of June.

The man works in the freight industry, but is not a truck driver and is not the positive Blue Mountains case as was largely speculated.

“A man from Melbourne came into a workplace in Sydney, and then there’s some transmission within that workplace and then they all went to a party that night of the third of July, at the Crossroads hotel,” Ms Musto said.

“So this is where it all began.”

This particular “patient zero”, unaware he was carrying the disease, then became linked to six colleagues who also attended the party and also tested positive.

“From there, we’ve uncovered an additional 32 cases to the Crossroads Hotel and from there we’ve actually learned that the most likely link,” Ms Musto said.

“So as far as we know, this outbreak is well known to us and we’ve identified all links, at this point in time, but we’ll get new cases and we’ll have to identify further links with them and for the contacts and get them all to go into isolation as well.”

Sharing insight into how contact tracing works, Ms Musto said teams spend an initial period of around 60 minutes on the phone with a positive contact, re-tracing their steps over the last 14 days.

In some instances the initial interview is just one of a number of phone calls as contact tracers piece together the moving parts of hundreds of people who were at a single pub at the same time.

NSW’s Chief Health Officer Dr Kerry Chant said the state was “clearly” dealing with cases that acquired the disease in Melbourne.

Overnight, NSW recorded 13 additional COVID-19 cases in 24 hours, 10 of whom are linked to the outbreak of cases from the Crossroads Hotel in Sydney’s south west.

Of that 10, six attended the hotel, two are close contacts of people who were at the pub, and another two caught the virus at the nearby Planet Fitness Gym.

The other three cases are returned travellers. The outbreak at the Crossroads Hotel has now been linked to 34 separate positive cases.

NSW Health Minister Brad Hazzard said he is immensely proud of the community for the way they have responded to shutting down the outbreak in Casula.

“I want to thank the community. We have an amazing community in New South Wales,” said Mr Hazzard.

“We have described this fight as a war, and when the war front comes back to us, our community has stepped up as frontline troops.”

NSW Health has completed 17,660 tests in the last 24 hours, bringing the total number of tests to more than 1.08 million.

A total of 51 people have died of the virus in NSW.