Comment by timr | Hacker News Reader

Comment by timr | Hacker News Reader

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Cochrane is the name of a literature database, not a method. It implies nothing about the quality of the research.

In fact, this is a meta-analysis of 138 papers from five different databases, and they say right at the top of the abstract that most of the studies were of poor quality:

"Study quality was poor for the three randomised controlled trials and most of the cluster randomised controlled trials; the observational studies were of mixed quality. Heterogeneity precluded meta-analysis of most data except that from six case-control studies."

The table you're citing says that they found an odds ratio somewhat better than frequent handwashing (55%), but worse than wearing a gown (77%) when they averaged the results of five different case-control studies, mostly in hospital conditions (the sixth didn't look at masks). Two studies investigated the use of N95 masks (specifically) at preventing infected people from transmitting their virus to others, and for these studies, they found a .09 odds ratio (with a wide confidence interval: 0.03-0.3), and they go so far as to say:

"Evidence was limited for the superior effectiveness of barrier devices to droplets such as the N95 masks...over simple surgical masks."

So they don't even believe the numbers.

This paper in no way supports the statement you made...in fact, it appears that you completely misunderstood what you read, because the only intervention with 91% effectiveness was "handwashing, mask, gloves and gown combined." But hey...if that's the way you go outside, good for you.

Please. Table 6.

Intervention: Wearing N95 Mask Intervention Effectiveness: 91%.

It's true that handwashing, wearing some kind of mask, gloves, and gown combined is also 91%, but that was not a study arm that specified an N95 mask. Wearing any mask has an intervention effectiveness of 68%. Adding the gloves and gown brings it up to 91%.

What the meta-analysis is saying is that wearing any mask + gloves + gown + handwashing is about the same effectiveness as wearing just an N95 mask. It also supports the idea that "don't touch your face" is probably good advice, but it's also probably not the primary means that SARS spreads. It's probably mostly breathing in droplets that someone just exhaled.

I understood perfectly well what they wrote. They say that evidence is limited for the superior effectiveness of N95 over any mask because the lower confidence interval of N95 and the upper confidence interval of any mask overlap by 5%. Based on the studies they analyzed though, it's likely that N95 is more effective than masks generally. It's also very logical since N95 masks filter better and have less leakage than surgical masks.

I am tired of people like you trying to bend science to their ideology. That is part of what got us into this horrible mess.

"Intervention: Wearing N95 Mask Intervention Effectiveness: 91%"

I addressed this in my reply: this was based on two studies, both about transmission of the virus to other people. Moreover, the people doing the meta-analysis explicitly say that the evidence for using an N95 mask over a plain-old surgical mask is weak. The confidence interval extends from 0.03 to 0.30...in other words, the evidence is weak.

So basically, this study supports the CDC's guidelines: masks might help prevent you from spreading your infection to others. They don't support your claim ("wearing an N95 mask reduces your chances of contracting SARS by 91%") in any way.

"What the meta-analysis is saying is that wearing any mask + gloves + gown + handwashing is about the same effectiveness as wearing just an N95 mask."

It is absolutely not saying this. It is saying that the combined intervention is dramatically more effective than wearing a mask alone, except for two studies that explicitly talk about transmission. You don't understand what you're reading, and you're spreading misinformation.

Table 6 for the N95 mask row cites w45 and w47. w47 had only 13 people in the study. And both w45 and w47 cite a medium risk of bias noting lack of description of controls and inconsistencies.

It would be nice to have more rigorous studies to support the claim?

Just to be clear, I do think people should wear masks!

Seto 2003w47 13 healthcare workers infected with confirmed SARS within 2-7 days of exposure, with no community exposure

w45 330 probable cases of SARS reported to Department of Health, Hong Kong

And by the way, when I do go outside, it's with a P100 mask, goggles, and gloves. I leave my shoes outside, go in through the garage, take off my clothes, throw them in the washing machine, sanitize my hands, and then take a shower.

For god's sake, this thing is so serious that we're not allowed to go outside for normal activities or go to work. We are all prisoners on very limited work release. If you're not taking extreme measures to protect yourself, you're an idiot.

Since this is important to you I feel the need to tell you that your doffing procedure is incorrect and will lead to you being infected. You're missing two hand-washings. If you're removing your mask in the same room as all the other stuff you're potentially breathing in infected particles.

Here are three doffing procedures specifically for covid-19:

https://twitter.com/EMedSligo/status/1245948283576561670/pho...

https://twitter.com/DisneyBen/status/1245224791122030592/pho...

https://twitter.com/ashaukat09/status/1245169306234769408/ph...

This is supported by your Cochrane review:

> Compliance with interventions—especially educational programmes—was a problem for several studies, despite the importance of such low cost interventions. Routine long term implementation of some would be problematic—particularly maintaining strict hygiene and barrier routines for long periods, probably only feasible in highly motivated environments such as hospitals without the threat of an epidemic.

Something like 80% of infection of healthcare professionals happens during doffing. These are people who are trained to don and doff PPE, and who are supported to do so by their infection control teams. https://twitter.com/drbencb/status/1236635924274057216?s=20 https://twitter.com/NydahlPeter/status/1244875837448638464?s...

Thanks!

The other comment on this subthread is such a comprehensive rebuttal to your paranoia that I can't add much. But I do want to say this: you should feel ashamed that you've taken valuable medical supplies from front-line responders. There are global shortages of masks and eye protection.

You don't need this equipment, and your paranoia is risking the lives of other people who do.

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