Stay Indoors - But Is That Enough?

 

Any casual reader of this blog might know that I was interested in indoor air quality including airborne viruses – long before it became fashionable. That had various origins including an undergrad focus on ecology, being raised by two heavy smokers, having to manage a coal fired stoker as a kid, working in a HEPA filtered clean room as a research assistant, and routinely getting viral respiratory infections in a hospital staff setting where we were all advised that hand washing was supposed to stop the mini-epidemics. And having asthma through all of that.

The indoor air quality issue has become complicated as our outdoor environment deteriorates. As an undergrad 50 years ago, we studied air pollution scenarios that affected large cities.  That included the concept of how smog was created by photochemical reactions but a lot of the specifics were not known.  More recently the entire Midwest and Northeastern US has been blanketed by wildfire smoke from Canada. Wildfire smoke is chemically complex.  In a lot of areas there are air quality alerts on one day due to wildfire smoke and ozone the next day. Those alerts are graduated to advise people with health conditions like asthma, emphysema, and heart disease on the lower end to limit outdoor activities or stay inside.  At high levels everyone gets the same advice.

The advice to stay inside assumes that your indoor air quality is better than the outdoor air quality that you are being warned about.  But is that a valid assumption?  How do you get measurements on everything and know the critical differences?  A good place to start is the outdoor air quality. The EPA has developed a nationwide network of sensors that detects particulates and ozone in the air and calculates the air quality index.  The AirNow app is available for your smart phone.  It gives you the outdoor reading, particulates, and ozone, as well as the break points from Good (0-50) to Hazardous (301-500). It will give you conservative advice about what to do about health and activity for those break points.

The CDC has a publication on indoor air quality in airports (1) where smoking was allowed. It provides some more intuitive markers of indoor quality. They found that the PM 2.5 (<2.5 micron particles per cubic meter) were 300+ in the smoking areas and 50+ in the areas adjacent to the smoking areas.  300+ levels are considered “very unhealthy”.  Anyone who has ever been in a smoke-filled room can probably sense that the atmosphere is not very good for your health either immediately of after leaving.  In Minnesota when the AQI was greater than 300 due to wildfire smoke – you could smell the wood fired smoke.

With an accurate assessment of the outdoor air – what about your indoor air quality?  I was fortunate enough to have purchased an air cleaner for my office with a PM 2.5 measure built into the machine. It usually reads in the 1-5 range but when the wildfire smoke arrived it was suddenly reading 40+ indoors. I had to figure out why that number was so high.  I had just replaced my furnace and it has a MERV13 filter that should provide some filtering efficiency.  The question mark was how my air exchanger fit into the mix.

My house is about 15 years old and like most modern houses it is considered airtight.  The concern by builders and contractors with modern homes is that they are so airtight that it leads to indoor air pollution from a number of sources including any combustion processes in the home and volatile compounds in the air from various sources like cleaning products.  As a result, air exchangers are installed to vent the indoor air and bring in fresh outdoor air.  These air exchangers are designed to reduce heat exchange and most do not have HEPA ( High Efficiency Particulate Air [filter])  filters.  They have a relatively primitive filtration system to remove mainly insects and very large particles. They can easily bring in outdoor smoke so it is a good idea to have it shut off on days where there is very high particulate matter.

The problem with my new system is that I was not sure that the air exchanger was off.  When my new furnace was installed the air exchanger was integrated into a touch panel with 30 different options and several ventilation settings.  I talked with 5 technicians (3 from the HVAC contractor, 1 from the air exchanger manufacturer, 1 from the smart thermostat manufacturer).  They all agreed shut off the air exchanger was a good idea but they gave me widely varying advice.  I decided to experiment myself over a period of 12 hours and generated the following graph (click to enlarge).

The first section shows the AQI outdoors versus indoors running the MERV 13 filter through the furnace.  There is no difference over that time period.  The next period I shut off the furnace filter and used a free-standing Space Gaard air cleaner with a MERV 8 (MERV = Minimum Efficiency Reporting Values) filter. Notice that during this time period the wind picked up outdoors, blew off some smoke and the PM 2.5 dropped from 160 to about 90.  At that time I talked with a 6^th technician and he gave me clear advice on how to shut off the air exchanger.  The last section is with the air exchanger off and all air circulating through the furnace filter MERV 13.  At that point the indoor AQ drops consistently despite a blip upwards in the outdoor PM 2.5 and continued to drop to 10.  To me that illustrates the importance of making sure the air exchanger if off when the outdoor AQ is poor and actively managing it to turn it one when the outdoor AQ is acceptable.

A related indoor AQ related to viral transmission is the carbon dioxide CO₂ levels.  Lower levels correlate with less people rebreathing air in the room and that decreases the risk of infection from airborne viruses. Outdoor CO₂ is roughly 400-420 ppm. My indoor measure is currently 570 without the air exchanger on.

There are currently PM 2.5 and CO₂ monitors available in most home stores and large online retailers.  What we really need is a more comprehensive single device that measures and records all of the parameters. I would suggest PM 2.5, PM 10, CO₂, Ozone, and Volatile Organic Compounds (VOC).  The closest I could come to that device was a gadget that required that I purchase a separate weather station and even then the bandwidth to multiple devices was limited.

Home HVAC system design could also use some innovation. Just based on my experience durability is a problem. Should an HVAC system last longer than 14 years?  Probably.  But the design itself does not seem very efficient.  I am not a certified HVAC tech by any means but it appears to me that the air exchanger introduces outdoor air into the system after the air filter so that any particulate matter in the outdoor air does not get at least one pass through the highest efficiency filter.

Outdoor air quality is a little discussed casualty of climate change. As the environment deteriorates, I expect that there will be increasing amounts of wildfire smoke and it will be chemically more complex. I currently wear an N95 mask outdoors during the alerts, but I can envision a time in the not-too-distant future where respirators that can also remove ozone and organic chemicals will also be necessary. Geography is no longer helpful in separating clean air from polluted air. Monitoring your personal indoor air quality and figuring out how to manage it will become the most critical part of home management. I have posted a few things that you can do right now and I am always interested in other ideas about how to address this problem.  Please post any of those ideas in the comments section.

 

George Dawson, MD, DFAPA

 

 

References:

1:  Centers for Disease Control and Prevention (CDC). Indoor air quality at nine large-hub airports with and without designated smoking areas--United States, October-November 2012. MMWR Morb Mortal Wkly Rep. 2012 Nov 23;61(46):948-51. PMID: 23169316.

2:  CDC Health Alert Advisory.   Wildfire Smoke Exposure Poses Threat to At-Risk Populations.  Link

Update 07/06/2023: 

One week after turning off my air exchanger - the PM 2.5 in my house is down to 6 or essentially normal.  I talked with my air conditioning tech who also services the air exchanger and he agreed with the approach.

Image Credit:

Canadian Wildfire Smoke in Minneapolis

Chad Davis from Minneapolis, United States, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

file URL:  https://upload.wikimedia.org/wikipedia/commons/c/c0/Canadian_Wildfire_Smoke_in_Minneapolis_%2852907984452%29.jpg

page URL:

https://commons.wikimedia.org/wiki/File:Canadian_Wildfire_Smoke_in_Minneapolis_(52907984452).jpg

Viruses Are In The Air - Protection From Airborne Viruses

Today was a good day.  I got up this morning and there on the morning news was a headline that I had been waiting to hear for at least 20 years.  There on CBS This Morning, Gail King was saying: "The flu can spread just by breathing so that is kind of scary."  That is kind of scary.  It is even scarier if you know that fact and listen to 20 years of how hand washing will prevent the flu. Hand washing is good only for surface contamination.  It does nothing for airborne viruses.  There is no known protection from airborne viruses other than biohazard environments.

I did not come by the knowledge easily.  Before medical school, I was a research assistance in a plant tissue culture lab.  Our job was to try to clone Loblolly Pine (Pinus taeda) and Douglas Fir (Pseudotsuga menziesii) trees from elite seed.  That required a sterile environment for tissue and media manipulations.  I spent much of the day working in a laminar flow hood bathed in sterile air.  We were not concerned at all about viruses at the time, but there were always experiments lost due to yeast and fungal contamination of the culture medium.  From there it was off to medical school and observations about just how contagious airborne viruses could be.  On some rotations the entire team was ill with respiratory infections.  I notice there is some movement today on telling physicians to stay home if they are sick.  If all of the people who were sick on one of these teams stayed home - there would be nobody there to take care of patients.  I did work with one attending physician who wore a surgical mask in a medicine clinic as a barrier to viruses.  Today we know that these masks are ineffective in blocking viruses.

The real eye opener came in practice.  For over 20 years I worked in an inpatient environment that was designed in the 1960s.  According to the HVAC experts I have consulted with, the environments in those days were designed to preserve heat.  They were not designed to provide fresh air in a manner that would minimize the risk of airborne virus infections.  All of the rooms in that environment had individual radiators equipped with fans.  The room air was recirculated.  At the top of each room was a 12" x 12" square vent that moved the air down  the length of the building to a few air shafts that traveled up and down between floors.  I was reassured that there was adequate air flow and that it was measured.  I was provided with some diagrams that did not really show any solid data.

In that environment, airborne viral infections ran rampant.  They were acute care psychiatric units - so many of the patients directly admitted had influenza.  It was just a matter of time before it was picked up by the staff and then transmitted from person to person.  Getting one or more of these infections predictably was quite depressing.  As anyone knows - a severe case of the flu disrupts your entire life.  The polypharmacy that the staff was subjected to was also impressive.  Long complicated courses of antibiotics for secondary infections after the flu had passed.  Exposure to prednisone and methylprednisolone for post-viral bronchitis and asthma exacerbations.  All of the infected staff were schooled in proper handwashing techniques by Infection Control.  During flu season we were basically adrift in tight confines - breathing contaminated air.  It is well documented by studies in hospital and other building environments that there are a significant amount of viral and other pathogens in the air that can be collected by a number of means (2).

The other enlightening experience involved my participation in two Avian Influenza task forces.  Practically all of the work that I saw being done seemed to ignore the issue of airborne spread.  That was probably at least in part due to the fact that the hospital capacity of negative air pressure rooms would be immediately overwhelmed.  At that point, I heard one expert say: "You need to have an N95 respirator mask on as soon as you walk through the door of the hospital."  The efficacy of those masks in preventing flu transmission is limited but probably offers some moral support when you are walking into an environment that is full of highly lethal influenza virus. Most of the planning done on the task forces seemed to be designed to prevent a large surge of patients going to the emergency department, providing psychological support to the overwhelmed, and hoping the military really did have that palette full of Tamiflu that they keep showing us in the PowerPoint presentations.

One of the questions I frequently get is - what about the vaccine?  Designing an effective flu vaccine is part science and part speculation.  It involves anticipating the viral strains of the next epidemic and that is difficult to know with certainty.  This is the first year that I can recall public health officials coming out with the actual numbers.  Most Americans have heard that this years vaccine is about 30% effective and that the most effective vaccines are 50-60% effective.  The argument is that the vaccine improves herd immunity and decreases the spread of the virus.  Exactly how much of that is cancelled out by broad exposure to an airborne virus is unknown, but I do think that is sufficient reason to always get the vaccination.  I was my own experiment for about 30 years.  I reacted to an anti-rabies duck embryo vaccine in my 20s and did not get the vaccine for the subsequent years.  I finally saw an allergist/immunologist about 7 years ago and have been getting the vaccine since.  Since then there has been no detectable change in the number or intensity of flu-like illnesses that I have developed.  During the time unvaccinated, I had the experience of developing an acute fever after being exposed to a colleague with the flu, taking Tamiflu (oseltamivir) and having the symptoms resolve within 24 hours.  There is a chance that a universal flu vaccine can be designed and I hope that is true.  In the meantime we are left dealing a number of airborne viruses and altering the environment seems like the best approach.   

Flashing forward to this morning.  Part of the story focused on Donald K. Milton and the work he did in designing a machine to sample flu viruses in a natural setting.  Other sampling techniques have typically involved subjects breathing according to protocol into a device.  The large reverse megaphone type of device that this group is using allows air flow past the face at a regular rate.  It allows research subjects to breath normally and sample their expired air for influenza virus.  The sample in this case was a group of healthy 19-21 year old college students with a high asthma prevalence (21%) and a low influenza vaccination rate.  Nasopharyngeal (NP) sampling and RNA detection was used to diagnose influenza and RNA copies.

The subjects were asked to breathe, talk, cough, and sneeze into the sampling device with no constraints on that activity.  They were asked to recite the alphabet at 5, 15, and 25 minutes.  Coarse droplets (> 5 μm ) and fine droplets (≤ 5 μm and >0.05 μm) were collected separately. Influenza virus was recovered from 89% (N=150) of the NP swabs and 39% (N=52) of the fine aerosol sample. This is positive proof that just breathing (tidal volume breathing) results in dispersing infectious viral particles into the air.  The influenza cases did not sneeze during the collection period. Viral shedding was greater for men.  Women coughed more frequently but shed significantly less virus per cough.  Increased BMI produced increased viral shedding in the fine aerosol and the speculation was that increased BMI causes a tendency for small airway collapse and that may lead to increased shear forces that produce the fine aerosol.  Since sneezing was not observed - it was not considered necessary to produce the fine or coarse aerosol.  Coughing was present and was a significant predictor of both coarse and fine aerosols.

 
This is a critical paper that I hope that all public health officials, administrators and architects will take note of.  It takes more than handwashing and coughing into your sleeve to protect people against influenza virus.  It takes recognition that this is an airborne virus and it is aerosolized by breathing.  Physicians are on the front lines when it comes to virus exposure and we need better barrier methods to prevent exposure.  During flu season I sit in a 8 x 10 foot office and talk with people who sit about 4-5 feet away from me.  I talk with most of them for 20-30 minutes or about the length of time of the experiment.  The symptoms listed in the severity scale below are incorporated into my review of systems and there are some days when 100% of the people I see have a respiratory infection.  If they all have influenza, 30% will leave aerosolized virus in my office just from talking with me.  Is there a better way to do things to minimize exposure?

I think it starts with building design.  Rooms that are all individually vented to the outdoors on both the intake and exhaust side.  Heat exchangers exist today and can be used for this purpose.  Starting with influenza as the model and optimizing air flow and humidity to decrease infection rates is a start.  Interviewing people across barriers or using television cameras is another possibility especially if vulnerable populations need to be protected from consultants who may be carriers. The tremendous lack of psychiatric infrastructure compounds the problem.  Although the building that I refer to was ultimately replaced and torn down - psychiatric services are typically housed in the oldest and most run down buildings.  Today jails have replaced psychiatric hospitals and the jail infrastructure is no better.  It is common to see patients who are acutely ill with influenza in these settings.  Psychiatric beds need to be in an environment that reduces the transmission of infectious diseases including airborne viruses.   

The work does not stop at that level.  The ways hospitals and buildings are cleaned needs to be thoroughly investigated.  Carpet and floor cleaning equipment clearly leads to the dispersion of particles in the carpeting or on the floor.  I am not aware of any initiative to make sure that cleaning the surfaces in buildings does not leave the air contaminated.

My advice is to spread the word and this reference to anyone who is unsure about airborne viruses. I am hopeful that at some point over the next 10-20 years the environmental aspects of the problem will be addressed.  That will change the nature of influenza transmission as well as a host of other viruses that get sampled in the HVAC systems of old buildings - probably long after the occupants have been infected by them.



George Dawson, MD, DFAPA


References:


1:  Yan J, Grantham M, Pantelic J, Bueno de Mesquita PJ, Albert B, Liu F, Ehrman S, Milton DK; EMIT Consortium. Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. Proc Natl Acad Sci U S A. 2018 Jan 30;115(5):1081-1086. doi: 10.1073/pnas.1716561115. Epub 2018 Jan 18. PubMed PMID: 29348203; PubMed Central PMCID: PMC5798362

2:  Airborne Virus Monitoring: unedited search



Supplementary:

Image at the top uses a crowd infographic from Shutterstock per their licensing agreement.

Supplementary 2:

This is the approach the authors used to scoring the flu symptoms severity in their paper (my interpretation) (click to enlarge):