Sunday, April 12, 2020

Studies that report Asymptomatic and Presymptomatic transmission of COVID19

This is the issue which I think explains both the world wide rapid spread and extreme difficulty of controlling this virus

It is a major worry. I have heard of reports of someone on a plane flight (to Alice Springs) later developing COVID19 and the other passengers not being tested because of the time lag. The assumption being that the virus is not transmitted while the carrier remains asymptomatic.

I googled and traced back the various reports to scientific references which were often provided in references. I’ve included a couple which are not referenced scientifically but still seem to provide important information. I’ve arranged them chronologically.

The American choir report also indicates that aerosol transmission can be a major factor, although singing would project the virus further than normal conversation. (see reference 7 in the Singapore study titled “Aerosol emission and superemission during human speech increase with voice loudness”)

These reports verify the importance of social distancing (and possibly mask wearing to prevent infection from people who are asymptomatic, but have the virus, from spreading it).

They do qualify an earlier WHO report from the team who visited China in February that the main spread was through family groups (extended contact) and through surfaces not aerosol. This may be true. But the minor transmission through the harder to track presymptomatic spreading helps explain why the virus spread so rapidly around the world.

The Singapore study, at the bottom, April 1, I thought contained the most interesting and easy to follow details.

Feb 14th
Wuhan Coronavirus by Rud Istvan (not a scientific study)
The bad news is that Wuhan IS transmissible during some later part of the symptomless incubation period. The definitive clinical proof ... is an age 50’s UK male who attended an about 100 person sales conference in Singapore 1/20-1/22 2020. A single individual from Wuhan also attended this conference and was–per Singapore Wuhan containment policies– symptomless on arrival (no fever, no cough). That either symptomless or very early symptomatic individual transmitted Wuhan to the UK citizen in Singapore. The UK individual then flew to France for a 4-day family ski vacation 1/24-1/28 at Le Contamines-Montjoie. During the 4-day vacation the UK male remained symptomless (entire incubation time Singapore plus France at most 8 days) but transmitted Wuhan to 11 other individuals, 5 later diagnosed in UK (family and friends), 5 later diagnosed in France, and 1 later diagnosed in Spain. Clearly this case is NOT family close proximity contact transmission. ...
February 18th
Evidence of SARS-CoV-2 Infection in Returning Travelers from Wuhan, China
Wuhan to Germany
“In this effort to evacuate 126 people from Wuhan to Frankfurt, a symptom-based screening process was ineffective in detecting SARS-CoV-2 infection in 2 persons who later were found to have evidence of SARS-CoV-2 in a throat swab. We discovered that shedding of potentially infectious virus may occur in persons who have no fever and no signs or only minor signs of infection.”
February 21
Presumed Asymptomatic Carrier Transmission of COVID-19
“A familial cluster of 5 patients with COVID-19 pneumonia in Anyang, China, had contact before their symptom onset with an asymptomatic family member who had traveled from the epidemic center of Wuhan. The sequence of events suggests that the coronavirus may have been transmitted by the asymptomatic carrier.”
March 19
Serial Interval of COVID-19 among Publicly Reported Confirmed Cases
US study (CDC) of Chinese data
“ ..12.6% of case reports indicated presymptomatic transmission.”
March 29
A choir decided to go ahead with rehearsal. Now dozens of members have COVID-19 and two are dead
USA, newspaper report, not a scientific study
Choir rehearsal, 60 members, on March 10th no one was ill
Nearly three weeks later, 45 have been diagnosed with COVID-19 or ill with the symptoms, at least three have been hospitalized, and two are dead.

The outbreak has stunned county health officials, who have concluded that the virus was almost certainly transmitted through the air from one or more people without symptoms.
April 1
Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020
LOTS OF IMPORTANT DETAIL – most convincing study
Investigation of all 243 cases of COVID-19 reported in Singapore during January 23–March 16 identified seven clusters of cases in which presymptomatic transmission is the most likely explanation for the occurrence of secondary cases...

In four clusters (A, B, F, and G), it was possible to determine that presymptomatic transmission exposure occurred 1–3 days before the source patient developed symptoms...

Presymptomatic transmission might occur through generation of respiratory droplets or possibly through indirect transmission. Speech and other vocal activities such as singing have been shown to generate air particles, with the rate of emission corresponding to voice loudness (7). News outlets have reported that during a choir practice in Washington on March 10, presymptomatic transmission likely played a role in SARS-CoV-2 transmission to approximately 40 of 60 choir members.*

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