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Comment by cameldrv | Hacker News Reader

I have a theory: From reading a bunch of case studies, it seems that the main route of transmission is microdroplets hanging in the air. A huge majority of transmission comes from being near someone for an extended period of time (30 min or so) indoors.

Since smoking is allowed in most casinos, they have extremely powerful ventilation and air filtration systems, so that their non-smoking customers aren't excessively bothered. If you've been in a Vegas casino and seen someone smoking, you notice that the smoke almost instantly gets sucked into the ceiling. This may dramatically reduce transmission in casinos or other venues that allow smoking.

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The initial 15 min rule (for whether you might get infected from close proximity to someone infected) was based on the idea that offices cycle their volume of air every 10 minutes, but casinos that allowing smoking may cycle their air more often.

This was often cited as a reason why everyone on a flight won't catch it, just those in nearby rows.

Vegas also doesn't have a subway system, which was cited as why it spread so rapidly in NY.

> Vegas also doesn't have a subway system, which was cited as why it spread so rapidly in NY.

There's no real evidence to support the thesis that the MTA was a primary vector of spread in NYC. Granular data of infection rate by neighborhood is spotty, but the data that does exist doesn't show any clear trends towards increased infection rates nearer subway lines. And the borough with the highest infection rate is the borough with the least transit ridership, and the borough with the lowest infection rate is that with the highest transit ridership...

(Source cite: https://pedestrianobservations.com/2020/04/15/the-subway-is-...).

Living in proximity to a subway line doesn't necessarily mean you spend more time on the subway than people who live further away, nor does it mean that you use the subway more. Subway commuters who can't afford to live close to a subway line probably live further from their workplaces, too, which would mean they spend more time on the subway and have more transfers between lines. Those people may then carry germs back to their neighborhoods.

The subway is a shared space with poor air quality and many hard surfaces that are touched by many people every hour.

The blog post you are "citing" tries to draw conclusions by zip code in a map that is not granular enough to support the claims. You yourself acknowledge this so I'm not sure why you use that blog post as evidence.

Also, Jeff Harris (the MIT professor who wrote the paper with which the blogger disagrees) is a doctor as well as being an economist. That doesn't mean he is infallible, but I wouldn't be so quick to dismiss his thoughts.

Agreed, boroughs with high transit ridership are going to be the big hubs, but very few of the people going through those hubs live in the immediate vicinity of the hub, and the people who do live in that vicinity may not have a lot of direct contact with those commuters. The whole problem with transmission through subway transit is that the people using that transit scatter to all and every corner of the region and beyond. They don't stay concentrated in the immediate vicinity of the transit system.

I use an inner city transit system every day on my usual commute, but the transit system hub I access it from is about 15 miles away from where I live. I use a bus and then a regional train network to get to it, then go into the underground.

I think it’s pretty clear that having a large portion of the city spend an hour a day packed together with 80 or so other people is going to increase transmission from a droplet spread disease.

As opposed to people living packed together in dense apartment blocks? Or working in crowded office blocks? Or spending leisure time in crowded recreational facilities? Or shopping in crowded stories? Or eating in crowded restaurants?

Yes, subways are crowded, but so is everything else in NYC. As for why NYC is doing much worse than other comparably dense cities worldwide, my thesis is that it's a failure at all levels of civic participation (federal, state, local, and even residential and commercial proprietors) to be proactive in counteracting the spread of coronavirus.

Below case study of Covid-19 spreading in a call center in middle of Seoul is pretty illuminating.

https://www.cnn.com/2020/04/30/opinions/eye-opening-south-ko...

The case study covers infections in a 19-story mixed commercial-residential building. First case was reported on March 9, 2020. The office seating diagram provided in the article shows extended (10 min or 1hr not sure), very close proximity spacing physically is the main reason for the spread.

Note that this was a call center so people were sitting and talking without masks on for extended periods.

* On March 9, one day after the first cases were reported, the entire building was closed. Testing was performed almost immediately on 1,143 people (workers, residents and a few visitors) with rapid results available to those affected and the team working to control the situation. The testing showed that 97 people (8.5% of those occupying the building) were infected. Most of the cases were women in their 30s and almost all (94 of the 97) worked on the 11th floor of the building, in the call center.*

I counted colored seats in the diagram and found 84 people in the call center got infected.

I think NYC got hit particularly hard because of subway cars. Enclosed in nearly airtight space for 10 - 30 minutes at a time.

More people in a single apartment will definitely increase spread. I'm not sure small apartments per se make any difference unless the ventilation is interconnected. I'm not sure how common that is.

I agree that everything is more crowded in NYC, but the only thing I can think of more crowded than a subway car is a nightclub. Estimating from ridership numbers, the average New Yorker rides the subway 15-30 minutes per day. The ceilings aren't even that high, just the number of people per unit volume is incredible.

One of the case studies I saw showed it spreading on a long distance bus between people sitting four rows away from each other.

https://youtu.be/R5K5ZBDPB3g

That’s rush hour. Let’s not kid ourselves.

Have you seen what the street above that station (note the station name) looks like during non-rush-hour situations? It's still that crowded.

(I'll also point out that you picked literally the busiest station on the entire system to use as an example.)

Just a quick YouTube search. I’m a life long long New Yorker, I can promise you that’s not the busiest. I can try to find you some video of the 7 line, it’s like that all the way from Grand Central to Main Street Flushing during rush hour.

The thing about the subway is that we all try to hold onto a pole or bar, total vectors for the spread. It’s not just an obvious case of being near each other, we’re forced to touch the same surfaces so we don’t collide every 30 seconds.

MTA says Times Square is the busiest station, by a not-even-close margin (63M annual versus 44M for #2): http://web.mta.info/nyct/facts/ridership/ridership_sub_annua...

Ah right, I didn’t even check to see the station. My larger point is there are many many stations that look just like that during rush hour.

I don't doubt you. But my larger point is that there are plenty of other situations in NYC where there's sufficient crowding for coronavirus spread.

Well, it may move the most riders, but if it has more trains the cars may not end up as crowded. OK way into nitpicking territory now :)

Interesting hypothesis. We should sill look at the evidence before stating it as fact.

In Wuhan, 11% of traced contacts came back to transport. One thing that might help would be to open the windows in the subway cars.

Rush hour cars have 200+ people in them and essentially no air circulation. Generally you're just inches away from people if you aren't outright touching.

No one actually lives in the borough with the most ridership, they just work there.

Rush hour on a subway is about as close as your going to get (no pun intended) to a clear cut ‘yep, this is how it spread’.

The idea that a subway system like New York's (or even more, London's) is NOT a major vehicle of disease transmission is an extraordinary claim that requires evidence more extraordinary than this.

Many places that are doing well (esp in Asia) have more extensive subway systems than NYC. However the people there might be more hygienic, or maybe the operators are cleaning more often.

The NYC subway seems to have a pretty unique local microclimate though. I don't know if it's just the lack of regenerative braking or if the close proximity to the iconic steam heating network is also playing a role in this, but compared to most other subway networks, the MTA feels like a living history museum - even if you close your eyes, block your ears and only take in the air. The influence of air heat and moisture on virus spread is quite complicated (evaporation ends some droplet classes, condensation ends others) so it's quite possible that some subway systems are much worse spreaders than others.

I think one thing is NY is testing like crazy. They're actually trying to find out just how many people are infected.

Some countries are still trying to avoid testing. Many Japanese hospitals are turning people away from testing unless they have severe symptoms lasting several days, so naturally, numbers look tiny. And let's be frank, China's numbers just shouldn't be believed.

According to worldometers stats, NY is at 40 tests per death, while the US average is at 100 tests per death. Spain and Italy are in the vicinity of 75 and even Belgium (hardest hit nation state in Europe) is still managing 55. New York is definitely not "testing like crazy", they are hardly keeping up. Portugal for example is at more than 400 tests/death, Czechia at 1000. Testing like crazy is what Singapore or Australia are doing.

You can’t hide excess deaths, at least in the developed world. Japan has not had 20,000 deaths.

Japan's population is lower than the USA. You're comparing absolute numbers when what you want is per million.

The US doesn't have high quality national excess death data, apparently. That's surprising. Part of the distorted response to this outbreak is because most countries only seem to publish relatively recent excess death data - often only a few years. But when longer term data is examined it shows that there have been plenty of flu seasons with similar death rates. That's why people keep comparing it to the flu.

At a national level the peak in the USA was at 20,000 excess deaths. In 2017 the peak was at about 7,000

(https://talkingpointsmemo.com/news/cdc-releases-detailed-nat...)

So it must be much worse, right?

Well, not really. If you look at the longer term data for a hard-hit country like the UK, where there are a lot of lockdown-created excess deaths due to excessively underloading the hospitals:

http://inproportion2.talkigy.com/

You can see that this outbreak had at the end of April an almost identical number of excess deaths so far this year to 2017, 1999 (which was worse), 1998, 1996 and 1995.

It seems flu care might have got better over time, or perhaps vaccinations had the impact. But so far the impact on COVID on the UK is not much different to disease outbreaks throughout the 1990s.

The UK stats will go up and it'll be worse than any other outbreak for sure, because at this point the population is in a state of fear and avoiding hospitals - even if they don't want to, critical treatments for other diseases have been cancelled to free up space for a surge that never came.

https://www.telegraph.co.uk/news/2020/04/27/care-homes-see-r...

"UK's biggest provider says deaths among residents at three times last year's rate, but only half of additional deaths linked to virus"

And this is with almost any death being ascribed to COVID, without requiring tests or evidence. The lockdown will claim more lives than COVID will.

> http://inproportion2.talkigy.com/

What a rubbish site. Its first argument is that deaths are not worse than 2018, so its not bad. Even though you can see that number of deaths quickly surpasses 2018 in 2-3 weeks and rises a lot higher faster, while it started a lot lower.

It's third argument is even more ridiculous. "Look at this graph showing a strong correlation between lockdown stringency and infection cases, stringent lockdowns increase infections!" is akin to saying people should stop using umbrellas because they increase rain.

(Also that graph is useless because the number of cases is not normalized inhabitants per inhabitants, so its x axis is bad)

>[...] look at the longer term data for a hard-hit country like the UK, where there are a lot of lockdown-created excess deaths due to excessively underloading the hospitals

talk about ridiculous claims.

There may be some basis in that. Excess deaths in the UK on a weekly level are higher than expected the number of covid deaths on a death certificate.

However this is only really in over 60s

The explanations would be

1) more covid deaths than have been mentioned on death certificate 2) more deaths from other reasons

I haven’t seen any detailed breakdown of cause of death other than “covid mentioned” (and thus not mentioned)

Or wear masks.

I've seen it plausibly argued that in e.g. Japan, they have a culture of not talking on your phone on the subway, and this substantially reduces transmission.

London just the same

https://www.theguardian.com/uk-news/2016/sep/29/tube-chat-ca...

This is true - not only do they have a culture of that, they have signs up telling people not to talk on their phones and to be quiet.

And angry elders who will glare at you violently if you don't adhere to the rule.

The vast majority wear masks and the operators wear gloves - and this is when there's not an active epidemic.

You get the impression that a lot of people in Western society would rather risk infection than be seen wearing a mask - defies logic.

You cannot compare situations in the US to situations in Asia since the populations are so different. In Asian countries people wear masks regularly... in the US the Vice President considered it too emasculating even for a HOSPITAL visit. There are plenty of good things about Americans but some of their worst qualities are a perfect match for disease transmission.

Or maybe because Vegas isn't Vegas (I mean this - https://www.reviewjournal.com/uncategorized/knowing-vegas-wh... ) and most of the participants came from abroad or other cities in the US.

So if people got contaminated there, in a couple of days they probably were somewhere else already.

Born n raised in Vegas. It’s a technical distinction that most locals don’t understand or care about.

I agree, but do Vegas COVID statistics mean cases only in Vegas or the adjacent cities?

As a similar example, a lot of people in NJ work in NY but a case on a NJ resident would be counted as NJ.

So, what happens in Vegas doesn't stay in Vegas.

On the one hand you say it won't spread in airplanes but will spread on a train, literally contradicting the sense between those two sentences.

Not a contradiction as it is not a direct comparison. Planes have substantially greater ventilation then trains on average.

They also have HEPA filters, etc.

Huh. Strong forced air evacuation is also common in restaurants, bars, and cafes in Japan, where until very recently smoking indoors was commonplace.

It's remarkable to me that there hasn't been an effort construct strong anti-covid ventilation/filtration systems, made even with air "disinfectant".

Then again, they can't even give health care workers PPEs.

I mean, HVAC systems are supposed to remain usable for 20+ years, it's not really something you can throw on a production line in a matter of days. Most likely, someone already is working on such a system.

They already exist, i saw a video on hvac systems used in a moroccan pop-up hospital, air coming in or leaving the building goes through filtration and then through a désinfection machine. They didn't explain the method used though.

I'd guess a strong UV-C light would kill the virus pretty reliably.

Normal HEPA filters can stop the virus: https://thewirecutter.com/blog/can-hepa-air-purifiers-captur...

Hospitals have had such systems for decades: Negative pressure rooms make sure that the bad air goes out through an exhaust that you can clean or at least keep well away from people. Some cars have HEPA filters, and airplanes often have more sophisticated systems than that.

There should be. There are a few options. UV-C in the air handlers seems like the easiest retrofit but I’m not sure how effective it is.

Casino airflow doesn’t explain the low rate for residents who don’t visit or work at Casinos.

Well, the primary reason you'd expect a higher than average rate in Nevada is Casinos. Without that, Vegas would have an average rate - plus, is Casinos are the main social outlet, those who don't go to Casinos might not go anywhere and be less likely to get the virus.

Las Vegas residents go to stores, restaurants, gyms, etc just like everyone else. Other than the casinos it's an average urban areas.

Right, which is why it would it would be an average rate without casinos.

Locals avoid Casinos unless they work there. I lived there only for a year but avoiding tourists was primary #1.

My Vegas-resident brother-in-law loved counting cards and betting on unpopular baseball teams, both of which involved entering casinos. Perhaps data is better than our two anecdotes?

Google mobility reports[1] show workplaces down 55% and retail and recreation down 47% for Clark County, Nevada (where Las Vegas is), and both dropped very quickly from March 13.

[1] https://www.google.com/covid19/mobility/ (Look for Nevada under the US)

Fair point, you’re right.

Look at Indian subcontinent, the entire Indian subcontinent has over 20% of world's population and yet couple of thousand deaths due to Covid.

I believe micro-droplets being evaporated by the notorious South Asian heat is playing a part.

They are apparently under an extremely strict lock down though.

Still I suspect the extreme differences between countries and even regions between countries will be studied for many years to come.

Google achohol lines in India. Tell me it's strict lockdown, it used to be, now it isn't anymore.

Call me back after Ramadan is over in PK.

Nice theory!

I heard a crazy theory from some foreign tourists visiting Vegas many years ago.

The story I heard is that Vegas hotels/casinos mix in small amount of certain gas/chemical in the circulating air that makes people not want to sleep, which makes people gamble more and spend more money.

Some crazy theories people have...

So I can see (as a non-expert) that the well ventilated casinos is the reason for low infection rate in Vegas.

NYC on the other hand has had the extremely highly infection rate because EVERYONE has to take subway and pretty sure there's not much air circulation in the subway cars...

Either way, I think not spending too much time indoors is the key to avoid covid-19. Unfortunately most all indoor space has recirculated, air-conditioned, stale air.

Edit: I personally think businesses that can leave windows open for fresh air will have lower chance of spreading Covid-19 than ones with barely functioning AC system with little air circulation.

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