Thread by @CrabbBrendan

Thread on my routine for personal risk assessment for airborne infections. A surprise at the end, that provides a compelling additional reason to monitor CO2. 1/

During last week’s regional @WorldHealthSmt conference, @DrBronKing and I traveled on a bus for a 15 minute trip with 30 or so other delegates. As the reading on the CO2 monitor shows, this was high risk for COVID/flu transmission. It was an easy risk assessment; we both wore our N95s masks. But, despite being COVID-conscious, I don’t always wear my N95 indoors. How do I decide when to do so? 2/

I always carry with me the two core tools of personal protection; a CO2 monitor and an N95 mask. I wear an N95 mask if CO2 readings are higher than 1,000 (I’m in the process of revising that down to 800ppm for reasons I will explain another day), or if someone around me is unwell regardless of the CO2 reading. Most days there are situations where I wear an N95 mask. Instead of always double checking that I have my wallet and keys when I leave the house, I now include a pocket sized CO2 monitor and an N95 mask. It’s that routine. That is a personal approach, others do it differently (& prob better). 3/

As an important aside, while I’m privileged to afford interventions like these and others I will mention, there are relatively inexpensive CO2 monitors out there and they last for ages, and while N95 or equivalent masks are expensive (generally $5+ each), each of mine lasts a month or so. I carry 2-3 with me always and rotate them, occasionally leaving them in the sun allowing the UV to decontaminate them. These two tools are the bedrock of personal protection against airborne pathogens. Without a CO2 monitor, the only safe way is to wear your mask all the time when indoors. 4/

The conference was in the extraordinary MCEC in Melbourne is a very large volume and well mechanically ventilated space, reflected in CO2 readings well under 800ppm in most spaces I was in. That was not always the case in smaller more crowded meeting rooms, and so in those instances I worse an N95 mask. 5/

One of the highest risk spaces for me is my home. I have young children who attend primary school, schools being a major source of community acquired COVID and flu. I don’t wear a mask at home unless one of us knowingly has COVID - we do test frequently. Our mitigation for this is to have all spaces well ventilated if we can (eg, windows and internal doors ajar), and with hepa-filtered air purifiers in most rooms 6/

https://x.com/CrabbBrendan/status/1777298243048927396

Airborne controls are one of the 3 layered protections we have for COVID-19 and influenza, the others are vaccination and testing (and acting on that test result). Using all three is important. On the one occasion when one of our children was infected, it did not transmit to the rest of us in the house. On an occasion when I broke my own rule (badly) I got COVID. With the world awash with COVID I will likely get it again, but with these measures I’m confident that my frequency of reinfection will be lower than the norm - and that matters a lot given the risk of LC each time you get infected is similar. 7/abc.net.au/news/2024-01-2…

As many who follow me know, apart from following my personal “mask above 1,000 (now 800)” rule, for extra protection in meeting rooms, restaurants and the like I carry a small personal air purifier. I don’t think it’s wise to heavily rely on these but there is evidence that they make a positive contribution to breathing cleaner air indoors. 8/

https://x.com/CrabbBrendan/status/1640160101830135810

However, pretty much all of the ‘personal protection’ approach described above is a stop-gap solution, until clean indoor air standards are developed and implemented. We are going through the equivalent of a ‘boiling our own water’ period for indoor air. In high income countries, clean water is a given because public health, engineering and regulations have come together to ensure that’s the case. We can do the same for indoor air. After a frustrating period, the world is well on the way to doing this. 9/

https://x.com/CrabbBrendan/status/1773886811728920987

A short-term practical implication of these will be the requirement of many indoor settings to monitor and display the indoor quality parameters in an easily digestible way. That means, you will know when you enter a room if it’s safe or not. This is happening in Belgium already for example. 10/nature.com/articles/d4158…

In summary, I remain personally COVID-conscious and have developed a regular routine that I do not find difficult to maintain (noting my privileges). Key points are:
1. I always carry an N95 mask and pocket-sized CO2 monitor
2. I wear my mask indoors at readings above 1,000ppm (will be reducing to 800ppm from now)
3. The world is on a pathway to clean indoor air standards, which will mean we’ll be safer while not having to think about it so much
4. Implemented clean indoor air standards, especially in high risk settings, promise to broadly improve health, school and work attendance and productivity
5. Cleaner indoor air offers powerful passive protection against airborne pandemics; both the one we’re still in and the ones we are yet to face. 11/

Postscript. Note this. While the science in this is not my comfort zone, the observation that increased CO2 is more than a marker of poor air quality but that it directly contributes to aerostability and hence infectivity is remarkable. This makes it even more compelling to monitor CO2 in indoor spaces and to ventilate naturally or mechanically to keep CO2 low. 12/

https://x.com/ukhadds/status/1783750076105384279

@WorldHealthSmt @DrBronKing Postscript 2. Big thanks to @DrBronKing for her help with this thread & wise counsel.