A strain of Covid-19 behind an outbreak in South Australia may be spreading up to five times quicker than normal, officials fear.
Concerned health bosses say the incubation period — how long it takes for someone to show symptoms after getting infected — was ‘very very short’.
Professor Nicola Spurrier, chief health officer for South Australia, claimed people are becoming contagious within 24 hours of catching the virus. She said the particular strain behind the outbreak had ‘certain characteristics’.
In theory, this could make the virus spread five times faster than usual, considering the average incubation period for Covid-19 is around five days.
The unique characteristics of the strain may explain why the state — home to around 1.7million people — went into a six-day lockdown despite only having 36 cases. All of them were recorded since Sunday.
Professor Spurrier suggested the contact tracing system was struggling to keep up with the spread.
People queue at a supermarket in Adelaide after the six-day lockdown was announced
Discussing the decision to enter a circuit-breaker, Professor Spurrier said at a press briefing: ‘This particular strain has had certain characteristics. It has a very, very short incubation period.
‘That means when somebody gets exposed, it is taking 24 hours or even less for that person to become infectious to others.’
It takes an average of five days before a person develops the tell-tale signs of Covid-19, which includes a fever and persistent cough.
But it can take up to 14 days, hence the reason for the UK’s 10 to 14 day self isolation period after coming into contact with a positive case.
In those days prior to symptoms, patients may be infectious and can pass the deadly virus onto others.
Transmission is most likely one day before symptoms begin, research has typically found, but can happen as early as three days before.
Professor Spurrier added: ‘The other characteristic of the cases we have seen so far is they have had minimal symptoms and sometimes no symptoms but have been able to pass it to other people.’
The rapid spreading capability of this strain meant a new ‘generation’ of cases was cropping up around every three days.
In epidemiology, patient ‘zero’ is the first generation. Whoever they pass the illness on to will be the second generation, and so on.
Professor Spurrier said: ‘At the moment in SA we have done contact tracing to the fourth generation but the fifth generation is out there in our community.’
Controlling pre-symptomatic spread is crucial for keeping on top of the disease and preventing deaths.
It hinges on the success of contact tracing, which involves rapidly identifying all the individuals who have been in close contact with a confirmed case, and telling them to self isolate before they are capable of spreading the virus further.
The short incubation period of a coronavirus strain makes it even more challenging to carry out contact tracing because it shortens the window in which a person is not contagious.
But Victoria’s acting chief health officer and epidemiologist, Professor Allen Cheng, is sceptical of claims of a more infectious strain.
A ‘simpler’ explanation is that the incubation is no shorter than usual, and rather the contact tracing system is so robust that it is finding the cases earlier, he told The Guardian.
Professor Mary-Louise McLaws, an epidemiologist and adviser to the World Health Organization, said there were always people who became infectious as soon as day one.
Professor Spurrier did not clarify how health chiefs came to the conclusion that the transmission was occurring from day one of infection.
Another explanation is that tests are simply picking up people who are carrying the coronavirus who may not be infectious yet.
South Australian Premier Steven Marshall announced the radical restrictions in a desperate bid to quash the virus before it gets out of control
Under the emergency measures only one person per household will be allowed to grocery shop. Above, a massive queue forms outside an Adelaide Woolworths on November 18
The outbreak emerged from an Adelaide hotel used to quarantine travellers from overseas. The ‘patient zero’ is a returned traveller who arrived from overseas on November 2.
Australia closed its borders to foreign travellers in March but has allowed citizens and permanent residents to return home, but only if they undergo a mandatory 14-day quarantine in a hotel.
It’s been confirmed the disease spread into the community after a cleaner at the Peppers Hotel came in contact with the virus and then infected members of her family.
So far more than 4,000 people have been either taken into quarantine or asked to isolate at home because of the outbreak.
Total diagnosed Covid-19 cases increased from 20 on Tuesday to 36 on Wednesday, and Professor Spurrier described the outbreak as a ‘worrying situation’.
The sudden Covid outbreak in South Australia ended six months of no community transmission of the virus.
Australia as a whole had recently squashed the coronavirus to almost zero cases per day after experiencing a huge ‘second wave’ in July and August, centered in Victoria.
Under South Australia’s six day ‘circuit-breaker’, which started on 12.01am Thursday, some of the most toughest measures are being used.
Schools, shops, pubs, factories and even takeaway restaurants were told to close at midnight.
The standard stay-at-home orders were issued for residents across the state. Only one person per household will be allowed to leave the house for medicine or groceries.
The rules even go beyond the strict regime of Victorian Premier Dan Andrews, who was dubbed a ‘dictator’ for keeping Melbourne under curfew and banning residents from going further than 5km from home.
Australia has recorded about 27,800 coronavirus infections and 906 deaths.