[morte-vivante]

By April 9, the contact tracers were becoming desperate. So they called up the profiles of everybody living in the same residential apartment tower as the earliest known sufferers.

One, they realised, had recently travelled from the United States – and she lived on the floor above the woman and her daughter.

A quick assessment revealed her to be well. And she's been following self-isolation protocol to the letter. But a swab revealed she had Covid-19 antibodies.

Detailed questioning and movement tracking showed the women had not come in direct contact with each other. Which left just one possible source of contagion.

The lift that portion of the apartment block shared – the asymptomatic traveller had used it to get to the apartment where she had self-isolated.

"Therefore, we believe A0 [the traveller from the US] was an asymptomatic carrier and that B1.1 [the daughter] was infected by contact with surfaces in the elevator in the building where they both lived," the researchers wrote.

Covid-19 coronavirus: Superspreader - woman infects 71 people in 60 seconds in elevator: CDC study

The implications of silent transmission for the control of COVID-19 outbreaks

the effectiveness of symptom-based isolation in preventing a resurgence depends on the extent of presymptomatic and asymptomatic transmission. We evaluate the contribution of presymptomatic and asymptomatic transmission based on recent individual-level data regarding infectiousness prior to symptom onset and the asymptomatic proportion among all infections. We found that the majority of incidences may be attributable to silent transmission from a combination of the presymptomatic stage and asymptomatic infections. Consequently, even if all symptomatic cases are isolated, a vast outbreak may nonetheless unfold. We further quantified the effect of isolating silent infections in addition to symptomatic cases, finding that over one-third of silent infections must be isolated to suppress a future outbreak below 1% of the population. Our results indicate that symptom-based isolation must be supplemented by rapid contact tracing and testing that identifies asymptomatic and presymptomatic cases, in order to safely lift current restrictions and minimize the risk of resurgence.

Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV-2)

We estimate that 86% of all infections were undocumented [95% credible interval (CI): 82–90%] before the 23 January 2020 travel restrictions. The transmission rate of undocumented infections per person was 55% the transmission rate of documented infections (95% CI: 46–62%), yet, because of their greater numbers, undocumented infections were the source of 79% of the documented cases. These findings explain the rapid geographic spread of SARS-CoV-2 and indicate that containment of this virus will be particularly challenging.

Two hairstylists who had coronavirus saw 140 clients. No new infections have been linked to the salon, officials say

No cases of coronavirus have been linked to two Missouri hairstylists who saw 140 clients last month while symptomatic, county health officials said.

Both stylists worked at the same Great Clips location in Springfield. The clients and the stylists all wore face coverings, and the salon had set up other measures such as social distancing of chairs and staggered appointments, the Springfield-Greene County Health Department said this week.

maar hé, #nomask4me eh