Adjusting Indoor Air May Be The Key To Reducing COVID Infections

The pressure to reopen the economy has pushed most of the country to loosen restrictions.  Restaurants, stores, and bars are booming with visitors eager to regain a sense of normalcy. But is it actually safe?  What does science tell us about how well we’re doing to stop the spread of COVID?

The number of infections is rising in many places.

The latest numbers show a disturbing rise in reported cases. 18 states are seeing upward trends in newly reported cases from one week to the next and 10 states are seeing steady numbers of newly reported cases.

In fact, the newest estimates predict 200,000 US deaths from coronavirus by October 1 — an increase of 30,000 deaths since last week’s projection by the Institute for Health Metrics and Evaluation at the University of Washington.

Should we go back to lockdown?

Strict lockdowns would likely be the most effective way to curb the spread of COVID. However, economic fears and public restlessness make another lockdown unlikely. A more realistic approach might be to understand how the virus is passed and find ways to live with it.

What have we learned about how the virus is spread?

Most scientists agree that COVID-19 is spread primarily through droplets in the air.  These droplets are released every time we cough, sneeze, or even breathe.  Mask wearing and social distancing have shown to be helpful in keeping the virus from transmitting from one person to another.  But, many believe that those measures don’t go far enough.

How far apart is far enough?

One of the arguments about social distancing is how far apart we need to be to avoid passing the virus. The WHO’s 3-foot distance recommendations come from William Wells, a Harvard researcher who studied tuberculosis in the 1930’s. He found that droplets that are emitted when we cough, breathe, or sneeze tend to land within 3 feet of where they’re expelled. The CDC goes even further, recommending a 6-foot distance between people.

But some scientists think that even 6 feet might not be far enough. A new study, published in Physics Of Fluids used a simulated aerosol spray from a cough. It found that with a wind speed of just one mile per hour, a significant amount of droplets can travel up to 20 feet in less than 2 seconds.

Does that mean we need to stay 20 feet apart?

Not likely. Dosage and exposure time are both factors in determining if someone actually contracts COVID and scientists still don’t have exact numbers on either.  But, most agree that the 6 feet distance is generally enough for outdoors.

But what about indoors?

If droplets can carry that far outdoors, what does it mean for indoor areas where air is often recycled? There are several factors involved. One of the most important questions is how many liters of air a person is getting per minute. Buildings, cruise ships, and air planes generally have a system whereby a portion of the air is pumped in from outside and a portion is recirculated indoor air.

Using a HEPA filter to clean the indoor air gets rid of 99% of viruses that are larger than .3 microns in size. This is why planes have decent air, considering the small enclosed area.  All of the air in a plane travels through HEPA filters before being pumped back through the cabin.

The effects aren’t nearly as positive using a lower quality air purification system. The Diamond cruise ship was docked in Tokyo Bay for nearly a month without HEPA filtration. 700 people became ill and 8 died.

Unfortunately, many buildings are also lacking in high quality air filtration.  Systems without HEPA filters catch only around 20% to 40% of viruses passing through.

Is a HEPA filtration system the best way to keep indoor transmission rates low?

HEPA purifiers show a lot of promise in lowering the infection rate, but humidity may also be a big factor. Stephanie Taylor, infection control consultant at Harvard Medical School, has conducted multiple studies showing that an indoor humidity level of between 40% to 60% has the potential to drastically reduce infection rates.

In 2013, Tayler studied how infections spread at a new hospital.  After isolating almost every other factor, she discovered a strong correlation between infection rates and humidity in patient rooms.

She continued her research at nursing homes and schools and found more evidence to validate the connection between mid-range humidity and a reduction in illness transmission. She concluded that there are three main reasons that humidity impedes infection rates.

  • Large droplets stay in the air longer when the air is dry.

  • Airborne viruses that thrive in winter (like coronavirus) aren’t as infectious in moist air.

  • Respiratory immune systems work better in greater humidity.

What will the future look like?

While no one knows for sure, It seems likely that COVID will continue to impact us in the next months or even years. Until a vaccine or highly effective medication is available, we’ll have to continue to find ways to limit our risk of exposure. Combining masks and social distancing with indoor air that is clean and humid may be the safest way forward.

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