29 April Part 1 Contact tracing

Thu, 04/30/2020 - 21:10

Dear colleagues,

Because of various activities, I had a lot of literature to catch up.  Therefore, this will be a rather long mail with some new info on epidemiology and diagnostics

  1. Epidemiological aspects
    1.  An interesting study on contact tracing (+ NP swabs) in Shenzen (North of Hongkong) shows that onward transmission was less than 6 % (11.5 in households), that children are as sensitive to transmission as adult (but much likely to show signs of disease) and that only 20% of PCR positive contacts were asymptomatic and 3 % had severe disease. Remarkably also, 80% of transmissions were caused by 9 % of the index cases, arguing for “superspreaders”  and the observed reproductive number was only 0.4. So, I guess, either the measures had already a downward effect  on transmission or possible transmissions were missed. Also, although this study nicely confirms that the virus doesn’t care about the age with regard to susceptibility to infection, we still have no answer to the question whether children are as infectious as adults or not….


    1.  The population-based  information from the village of Vo in Italy, where a large part (75 %) of the population was swabbed twice, before and after 2 weeks of lockdown, in response to the first Italian COVID death on 21st February, provides a slightly different picture.    In the  first survey 73 people (2.6 %) were found to be infected; in the second survey only 8 new cases were found.  Table 1, 2, 3 p. 20-21 show the most interesting results.  In Vo over 40 % were asymptomatic and most infections in the first survey were found in older subjects 54/73 in the 50-80+ group and only 3 in children ( <20 years).  Modeling showed that the lockdown had a dramatic (90 %) decreasing effect on transmission. Another remarkable finding is that viral load (estimated from CT value) was similar in asy and sympt. Individuals and that apparently 4/6 of the new infections in the second survey were acquired from ASY household or other contacts.  


    1. In follow up of our discussion of least week on the reliability of death rates by COVID in various countries, you may remember that, according to NY Times amongst various European countries, only Belgium and Sweden provided a reasonably good estimate of COVID deaths (see  first Word document).  Now a similar study was published in The Financial Times, showing that excess deaths early April varied widely across European countries See https://www.ft.com/content/6bd88b7d-3386-4543-b2e9-0d5c6fac846c?utm_source=Nature+Briefing&utm_campaign=527dbb4637-briefing-dy-20200428&utm_medium=email&utm_term=0_c9dfd39373-527dbb4637-44799709
      and summary in second Word document in attach. As you can see, the excess is widely different from only 5 % in Denmark to 90 % in Italy.  But again Belgium (60%) ranks second after Italy…. On the second page, you see even much higher rises in cities like Bergamo (+ 460%), Guayas (+370 %) and NYC (+ 300%). Remarkably also, while the whole of Sweden has only a rise of 18 %, it is 75 % in Stockholm.  Hence, possibly, there was hardly any rise in mortality outside of Stockholm?  


    1. SARS-CoV-2 in aerosols (Nature paper): this paper confirms “common sense” in a way.  Crowded, poorly ventilated places such as mobile toilets, certain staff rooms… contain quite some viral RNA in the air: in the range of 20-100 particles per m3.  The concentration can be drastically reduced by better ventilation and proper disinfection.  Obviously this is only “presumptive evidence” that virus-laden aerosols could have a role in transmission, as infectious virus was not measured and we simply don’t know what the threshold value of viral particles per m3 air for infection could be….    


1.5  Christian Drosten.  For those who understand German please watch and listen to this video https://tvthek.orf.at/profile/Additional-Content/1670/Langfassung-Interview-mit-Virologe-Christian-Drosten/14049580.  For all others, please read his interview with The Guardian in attachment.


  1. Diagnostic aspects: important simplifications
  • Saliva is a good, even more sensitive alternative for nasopharyngeal swabs:  on condition you spit enough representative morning saliva before  tooth brushing, eating or drinknig  in  a sterile urine container.
  • No strict need for the universal transport medium!

Best wishes,