COVID19 update, July 10, 2020: aerosol transmission; empirical studies on choir rehearsals and office buildings; some neighborhoods of NYC at herd immunity?; deaths in British care homes linked to contract labor

(1) Dr. John Campbell on airborne aerosol transmission

The article he refers to is this one:

In a nutshell: while a 1-2 meter “social distance” is useful against larger droplets (which fall to the earth), this does not apply to aerosols (made up of droplets of 5 micron or smaller) which can spread dozens of meters through the air and keep hanging for quite a whole. Your typical cloth or surgical mask will not be very helpful against aerosols either. (A true N95 mask, that conforms to the NIOSH N95 standard, is supposed to block 95% or more of particulate matter at  0.3 micron size.)

So what can you do? In a word: refresh the air. Outside activities are safest from an aerosol perspective (especially if there is at least some breeze), and small or tightly packed enclosed spaces with no air refreshment from outside are the worst. (I used to think planes would be the very worst, but Air Canada, in a recent mailing to me, claims that not only do they turn over all cabin air at a rate of one full refresh every three minutes, but they filter the air through HEPA filters.)

(2) Aerosol transmission: how dangerous is singing, really? A reporter from Die Welt (herself a member of the Berlin philharmonic chorus) discusses (in German)  a study by engineers from the Technical University of Berlin. 

The people involved are professionally mostly interested in the design of ventilation systems for large office buildings and residential complexes. As the whole issue of aerosol transmission of COVID-19 started coming to the fore, and reports of super-spreader events at choir rehearsals (notably this well-studied one in Washington state) and religious services with singing kept coming up, they asked themselves the question: can we empirically test and quantify this? Do singers spread more aerosol droplets than people speaking or going about their daily activities?

So they recruited eight volunteers from the RIAS Chamber Choir in Berlin and had them, inside a “cleanroom” breathe,  then speak, then sing at a range of volumes into funnels connected to a special apparatus in which a laser particle counter measures and counts aerosol droplets. A preliminary report (in German) is available  here on the university’s preprint server. The English abstract (some “Gerglish” corrections for clarity in square parentheses):

n this study, emission rates of aerosols emitted during singing are presented for professional singers. The results, measured with a laser particle counter, are compared with published data for breathing and speaking. In the investigated cohort of eight volunteers, the particle source strengths during singing are between 753.4 and 6093.14 [articles per second]. The [increase factor in emission] rates [when] singing [compared to] speaking [is] between 3.98 and 99.54. The present study contributes to a more precise assessment of a possible spread of SARS-CoV-2-viruses during singing. It should support the efforts to improve the risk management, especially for choir singing.

From Figure 4 of the whole report, we see also that the aerosol particle concentration (particles of 5 micron and smaller) was statistically well correlated (R**2 = 0.824) with the volume in decibels: Log10 (concentration) = 0.07 (volume in dB) – 2.41.

The researchers then carried out a second study (preliminary report here) in which they tried to see under which circumstances choir rehearsals could be made no more dangerous (from the point of view of aerosol exposure) than an ordinary office building. In their simulation, they achieved this for a given rehearsal room (the auditorium of a local school) by spacing the participants at 2m distance and, instead of having them sing for 2h at a stretch, sing for half an hour at a time with 15=-minute breaks during which all windows of the hall were opened wide.

Perhaps the most counterintuitive conclusion was that the audience and orchestral musicians at classical music performances in large halls, like those of the Berlin Philharmonic and its Dresden counterpart, are surprisingly safe, thanks to the very large and high-ceilinged halls and the efficient forced-ventilation system. (This was in place for very different reasons: reduce accumulation of CO2.)

Graph address:

This graphs shows the concentration of potentially infectious aerosol particles per square meter in different spaces. Lowest are the large, high-ceilinged  concert halls of the Dresden and Berlin philharmonics; above that is an office with forced ventilation, about the same as a choir rehearsal room with a single infected person; higher (in blue) is an office with just window air (presumably different if you sit by the window); and at the top is a choir rehearsal room with three infected participants. The descending segment in the middle represents the effect of a 15-minute “airing out” after 30 minutes. 

(3) The Daily Telegraph reports that some neighborhoods of New York have shown up unprecedentedly high percentages of positive antibody tests — reaching 1st-order herd immunity levels. 

Areas of New York have recorded a nearly 70 per cent rate of immunity to Covid-19, in what scientists have described as “stunning” findings that suggest they could be protected from any second wave.

Some 68 per cent of people who took antibody tests at a clinic in the Corona [you can’t make this up! — Ed.] neighbourhood of Queens received positive results, while at another clinic in Jackson Heights, 56 per cent tested positive. 

The results, shared by healthcare company CityMD with the New York Times, appear to show a higher antibody rate than anywhere in the world, based on publicly released data.

The next closest is the Italian province of Bergamo, which recorded 57 per cent, followed by Alpine ski resort Ischgl, the site of Austria’s biggest coronavirus outbreak, which reported 47 per cent.


Wealthier areas recorded much lower rates, according to CityMD data. For example, at a clinic in Cobble Hill, a mostly white and wealthy neighbourhood in Brooklyn, only 13 per cent of people tested positive for antibodies.

The results suggest higher-income neighbourhoods may bear the brunt of any second wave to hit the city.

CityMD administered about 314,000 antibody tests in New York City, as of June 26. Citywide, 26 per cent of the tests came back positive.

Tangentially related, Dr. Seheult here discusses immunity testing and survey data for Spain

The paper is here: They retained a sample of over 61,000 (the largest of its kind so far), and used two different antibody tests on each. For Spain as a whole, the seroprevalence is only 5%, but larger towns (and especially the Madrid area) have higher figures, as do health care and nursing home workers, and — interestingly — the top 5% earners (presumably because many such people travel a lot for work). At least one-third of people who has antibodies had never had any symptoms. 

(4) Also in the Telegraph, the story of deaths in British care homes seems more complicated than meets the eye.

It has been the same, awful story everywhere. Sweden didn’t lock down and has still had fewer deaths per capita than Britain (while taking a far smaller economic hit). But a failure to protect care homes led to most of Sweden’s Covid deaths. The figures here are quite striking: care homes look after three per cent of Britain’s elderly population but accounted for 41 per cent of our Covid deaths. Similar ratios can be found in Spain, France, Denmark, Israel and Portugal.

As a result, most of Europe is now asking what went wrong in care homes – and moving to a similar conclusion. It took ages to realise how many people are barely affected by Covid, carrying (and spreading) the virus without knowing it. Asking people to isolate if they had symptoms didn’t offer much protection. The more people coming in and out of the care homes, the greater the risk of infection. If those care homes don’t offer sick pay, the risk is greater.

Hong Kong banned care home visits pretty early on: it had learned from Sars. But British care homes were taking visitors for weeks after lockdown and, even after that stopped, agency workers drifted in and out, some working in multiple homes. The Government (belatedly) advised against this “where possible”. But for most homes it is not possible: they have no staff backup. Yet again, we see the problem in the British care home industry: a refusal to pay decent wages, a dependence on casual staff and a reliance on agencies that can provide low-cost workers.

Care homes that did things differently saw very different results. In France, a home near Lyon put its staff and residents into complete isolation for seven weeks, taking no one from outside. They had no Covid deaths. Valerie Martin, its director, said she went to such lengths because “my residents still have so much to live for”. She also had carers paid enough that they didn’t need a second job and were willing to be quarantined.

It has been a very different story here. An Isle of Skye care home found that 30 of its 36 residents ended up with the virus, six of whom died. It turned out to be shipping in workers, including one from Kent. [That’s literally the other end of the UK — Ed.] A study published last week tried to explain the huge differences in how homes in England were affected. Residents looked after by agency workers were 58 per cent more likely to contract Covid. Those working in multiple care homes were more than twice as likely to carry the virus.

It might be shocking. But it’s not really surprising – given that this is the same problem we saw during the spread of superbugs like MRSA. Those lessons weren’t learned. Care homes argue, still, that their business model depends on being able to pay people less than supermarkets do. Their complaint about Brexit, even now, is that it makes it harder for them to import cheap labour and keep wages down. Their bigger concern should be what the Covid crisis has shown about their ability to protect those in their care.

(5) The WHO discontinues the hospital arms of both hydroxychloroquine and lopinavir/ritonavir trials, on the grounds that they statistically are no better than standard of case.

Contrary to the misleading headline in the original, however, it seems that the shutdown only affects the hospital arm, and that the prophylaxis and outpatient arms of the trials are continuing. I would indeed not expect antivirals like lopinavir/ritonavir (and, indirectly, HOcq) to be very effective in the severe disease stage, at which point immune overresponse is your biggest threat, not the virus per se anymore.

ADDENDUM: David Friedman on the recent increase in verified cases not being accompanied by an increase in deaths.

One thought on “COVID19 update, July 10, 2020: aerosol transmission; empirical studies on choir rehearsals and office buildings; some neighborhoods of NYC at herd immunity?; deaths in British care homes linked to contract labor

  1. A topical issue is schools. Should schools reopen? Or continue with “distance learning” in the fall?

    RIVM is a Dutch research org predominantly funded by the national gov’t, the EU and the UN. Their recommendation is that kids under 18 years of age do NOT need to socially distance themselves.
    Community college students (and above) and teachers at all levels should maintain distance.
    I’ve read that Euro schools in general have been re-opening with no special issues.

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