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Mar 4

‘A real sleuthing exercise’: Every coronavirus case starts a race to track contacts – ABC News

Exercise Programs Comments Off on ‘A real sleuthing exercise’: Every coronavirus case starts a race to track contacts – ABC News

Imagine you've tested positive for coronavirus. Once you've been isolated from the public and treated, a health official comes to your bedside and asks for an interview: Who have you infected?

Who have you come into close contact with face-to-face and less than a metre for a period of at least 10-15 minutes in the last 14 days?

You think back: There's your family and friends and perhaps workmates too, but also less obvious candidates, like whoever you've sat next to on the bus, or shared a table with at a cafe, and maybe also your hairdresser or beautician or a taxi driver.

You may eventually come up with a list that numbers a dozen people, many of them strangers.

The work of figuring out who these people are and then contacting them before they infect anyone else is known as contact tracing.

With coronavirus spreading in Australia, teams of public health workers are engaged in a high-stakes race that's taking place mostly behind-the-scenes, but which will determine how many people are infected with Covid-19 in the coming months.

Professor Dominic Dwyer, a medical virologist and NSW Health's Director of Public Health Pathology based at Westmead Hospital in Western Sydney, is at the centre of this effort.

He described contact tracing as urgent and arduous detective work that begins from the moment a lab test comes back positive.

"It's quite complicated and quite time-intensive and money-intensive," he said.

"It's a real sleuthing exercise a lot of shoe leather gets used in trying to contact everybody.

"Something like this coronavirus one you've got thousands of people working around the world, following up cases left, right and center.

We have a team of people going, 24/7 doing the laboratory testing and [NSW Health] have a team going, essentially, 24/7 doing contact tracing.

Passengers arrive in Sydney.

In late January, two people tested positive for coronavirus after travelling from Melbourne to the Gold Coast on a 180-seat passenger flight.

In response, hundreds of passengers from 13 different flights were contacted.

"They followed up all the cases and sure enough they found a couple more cases in Queensland," Professor Dwyer said.

Tracking down plane passengers is relatively easy since passengers have to buy a ticket once an infected person gets on a bus or train, it gets exponentially harder.

A few days ago, a Gold Coast beautician based at a busy shopping centre was identified as Queensland's sixth Covid-19 confirmed case.

From the contact tracing interview, it emerged she had seen between 30 and 40 clients for treatments including facials and waxing before she went home sick. These customers turned out to be much harder to track down than passengers listed on a flight manifest. Authorities have asked anyone who visited the salon on that day to come forward.

"People are hard to find," Professor Dwyer said.

"In a country like Australia where there's free movement of people, it can actually be quite hard to find people, particularly when you want to do it very quickly."

The network map below, created at the epidemiology unit of the US Center for Disease Control (CDC) shows the spread of an airborne infectious disease.

Black nodes are persons with clinical disease (and are potentially infectious), pink nodes represent exposed persons who are not yet infectious, and green represent exposed persons who have not been infected. Grey nodes are people that are still to be tested.

The black node in the centre is a 'super-spreader'.

Earlier this month, a 61-year-old woman in South Korea gave at least 37 people at her church Covid-19 over the course of four services. She was a super-spreader.

By comparison, current estimates suggest that a single person with coronavirus spreads the infection to about 2.2 additional people, on average.

The more easily a disease spreads, the higher its basic 'reproductive number'. Any reproductive number higher than one means the disease will keep spreading.

Another important variable for contact tracing is the duration between the onset of symptoms in one person and the onset of symptoms in the person they infect.

The faster a virus multiplies in the body, the smaller this 'serial interval'.

Serial intervals have an outsized effect on the speed with which a virus spreads.

To see just how much, this interactive tool instantly updates projections based on different values for the reproductive number and serial interval. Reducing the serial interval by just one day can increase the number of projected cases within the following week by five times.

The serial interval for Covid-19 is estimated to be about 4.4 days - relatively low for a respiratory infectious disease (therefore it spreads quickly).

By comparison, the serial interval for SARS is seven days and for measles about 11.7 days.

What this adds up to is that coronavirus spreads relatively quickly, meaning contact tracers have less time to identify potential cases.

Each person on average has about nine close contacts, says Dr Raina MacIntyre, Professor of Infectious Diseases Epidemiology at UNSW.

"It varies from case to case, but on average we know that from contact tracing other infectious diseases each person on average has about nine close contacts," she told Hack.

Contact tracers attempt to "ring fence" an infected person by first identifying and testing their direct contacts, and then the contacts of these contacts.

These counter-measures effectively reduce the reproductive number of the virus.

However, in this instance, contact tracing is made doubly hard by the fact that some people with coronavirus can spread it even though they have no symptoms.

Some public health experts fear 'stealth' or 'cryptic' transmissions may already be occurring in communities in the United States.

"People who are asymptomatic can have just as much virus in their nose and throat as people who have symptoms," Dr MacIntyre said.

In China, authorities are using mobile phone data as well as facial recognition software to monitor individual patients and suspected cases in real time.

In one case, officials tracked an infected person across the city of Nanjing minute by minute and published the details of the patient's travels on social media to warn residents that they may have been infected if they crossed paths. This doesn't happen in Australia.

Basically, contact tracing is much easier in a surveillance state.

"You do run into, at some stage, an ethical dilemma over this," Professor Dwyer told Hack.

"Facial recognition, population movements, all of that sort of stuff are much easier to control in China than they are in Australia.

"Populations accept different levels of control."

Professor Dwyer worked with the World Health Organisation during the SARS epidemic in Beijing in 2002 and 2003. He says that authorities knew exactly where anybody was at any given time in a city of almost 20 million people.

"You basically could go down to the street level and say, 'So and so's home' or 'No they're not home' or 'They're at work' or whatever," he said.

Chinese authorities are actually able to get hold of people surprisingly given the population much more easily than in Australia.

A Chinese health worker checks the temperature of a woman entering a subway station.

Australian police are already sharing phone-tracking systems they use in criminal investigations to help public health officials with contact tracing.

Asked whether the spread of a deadly disease might give reason for increasing surveillance, Professor Dwyer said, "There's a discussion to have around the ethics of all of that and what's enough control and what's too much control."

"If we have someone who comes to the ED and they happen to have coronavirus and then they go home, you have no idea where they are.

"They might go to a pub or a music thing, and people don't know where they are at any given time. Whereas in China it's more controlled."

Professor Dwyer says contact tracing is a priority during the 'containment' phase of an outbreak, when the number of cases remains relatively low.

But given how hard it is to track people down, the contact tracing system is easily overwhelmed.

"Now, if it gets out of hand, and you suddenly have thousands of cases, well, then clearly you're not going to be able to follow them all up," he said.

However, that doesn't mean the end of all contact tracing.

Instead, the containment zone would shrink. Professor Dwyer gave the scenario of a "mega-outbreak in Sydney or Melbourne". Others parts of Australia may then trace the contacts people who have come from there, in the way they did for people from Wuhan in January.

You might have special groups in the community that you want to be very careful about containment. For example, our Indigenous communities - you want to stop these diseases getting into remote areas of Australia.

Asked for his thoughts on what's in store in the coming months, Professor Dwyer said he thinks there will be more cases in Australia, and they might spread.

"But I think it's unlikely we'll get the really nasty outbreaks we've seen in other countries.

"We've got pretty pretty good public health systems, we've got pretty good health facilities, we've got very good laboratories."

NSW Health told Hack Covid-19 is demanding a "whole of health response".

"Resources are applied as required in response to the evolving situation," a spokesperson said.

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'A real sleuthing exercise': Every coronavirus case starts a race to track contacts - ABC News

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