How One Person Spread Coronavirus to at least 71 People

We all realise by now that SARS-CoV-2 is highly contagious. But a recent cluster in China shows just how easily the coronavirus can spread.

On 19 March, patient zero for this cluster had returned from the US to China’s Heilongjiang Province. She had no symptoms and self-isolated on her own in her apartment.

Patient one lives downstairs from patient zero in the same apartment building. He uses the same elevator as patient zero, but not at the same time.

On 26 March, the downstairs neighbour’s mother and her partner visit him at his home for dinner. At this point, there has been no confirmed new Covid-19 case in Heilongjiang Province for 15 days.

On 29 March, the mother and her partner attend a party that’s also attended by an elderly man and his sons. Two days later, patient zero’s tests come back negative.

On 2 April, the elderly man has a stroke and is admitted to hospital. His two sons care for him at the hospital, making use of the ward’s kitchenette and microwave. 

The infection silently passes to 28 other people at the hospital, including five nurses and a doctor. Four of those infected never even entered the same ward as the elderly man.

On 3 April, patient zero’s serum antibody tests also come back negative.

On 6 April, the elderly man is transferred to another hospital after developing a fever. Twenty more people are unknowingly infected at this second hospital.

On 7 April, the downstairs neighbour’s mother’s partner notices symptoms of Covid-19. He tests positive on 9 April. It is now three weeks since patient zero returned from the US.

On 9 April, the downstairs neighbour, the mother and the elderly man and his sons are all tested. The tests come back positive on 10 April.

Also on 9 April, the tracing team identifies that a woman in the downstairs neighbour’s building (i.e., patient zero) recently returned from the US. She is administered an immunoglobulin test, which shows that she had previously been infected but remained asymptomatic.

The figure below shows the full map of infections. 

By 15 April, China’s Center for Disease Control has sequenced the genome of 21 of the infected patients’ samples. This demonstrated they’d been infected with a strain of Covid-19 that was not previously present in China.

The furthest infected person from patient zero is the neighbour of a family member of a patient who was at the second hospital at the same time as the elderly man who attended the same party as patient zero’s downstairs neighbour’s mother and partner. 

At least, that’s the furthest that we know of. After all, it all started with one asymptomatic carrier. If that doesn’t motivate you to socially isolate, I don’t know what will.