A new study on the earliest coronavirus cluster in Europe has found that while close contact between people resulted in infection that did not mean shared households and offices automatically led to the spread of the illness.
Fascinating insight into the virus' transmission rate has been disclosed in an in-depth study carried out by The Lancet medical magazine.
While the study repeated the disclosure that even glancing acts, like passing a saltshaker, could transmit the disease only half people sharing a small office room contracted the disease. It was key however that office occupants sat at a distance.
It also showed that infection could be contained within a self-isolating household if a virus carrier remained totally isolated.
The Lancet study was based on the so-called Bavarian Cluster of 16 virus sufferers in late January. Through the Germans' efficient contact tracing it shows the first documented chain of human-to-human spread of the Covid-19 outside Asia. It also details how the virus can spread via contact with objects such as computers and glass.
The rapid contact tracing is understood to have been vital in stopping the early spread of Covid-19 across Germany, a country that has seen a significantly less death toll than others such as Italy, Britain and France.
Because the cluster was based around a sophisticated German car manufacturer the scientists have been able to trace the movements of each worker via digital records.
The group was infected by Patient Zero who had flown in from Wuhan, China for a business trip. Zero infected Patient One when they had a business meeting in a small 12m squared room that lasted for one hour. While Zero and One sat next to each other, two other colleagues sat at the opposite side of the table. Patient One contracted the virus while the two colleagues tested negative.
Patient One is likely to have infected Patient Three when they both briefly worked together on the same computer.
While Patient Five did not meet Patient Zero, he did sit back to back with another infected worker in the staff canteen. It is almost certain that he contracted the disease after he asked for his colleague to pass him the salt shaker for his food.
The study also found that secondary attack rates - which refer to the spread of a disease in a family or household – “decreases with the intensity of contact: among members of the cohorted household, the secondary attack rate was 75 per cent, but decreased to 10 per cent among household contacts that were only together until isolation of the case.”
The study said although there was a high risk in close household contacts, such as by sharing a room, “strong measures” taken within a household could “prevent transmission”. This is understood to be quarantining someone within their room.
The study also found that the incubation period for the virus was 4.0 days whereas research in China had shown it to be 5.2 days and with SARS it was found to be 6·4 days.
The report found that infection before symptoms appeared or on the day of symptom onset “poses a huge challenge on the implementation of public health measures” with very short incubation periods.
It added: “Although the outbreak was controlled and therefore might have granted valuable time before more intense transmission occurred in Germany, successful long-term and global containment of Covid-19 could be difficult to achieve.”
The Lancet added it was fortunate that the group of workers were relatively young, with an average age of 35, and healthy, allowing scientists to study them in detail.