Jessica Green: Are we filtering the wrong microbes?

Humans in the developed world

spend more than 90 percent of their lives indoors,

where they breathe in and come into contact

with trillions of life forms invisible to the naked eye:

microorganisms.

Buildings are complex ecosystems

that are an important source

of microbes that are good for us,

and some that are bad for us.

What determines the types and distributions

of microbes indoors?

Buildings are colonized by airborne microbes

that enter through windows

and through mechanical ventilation systems.

And they are brought inside

by humans and other creatures.

The fate of microbes indoors

depends on complex interactions

with humans,

and with the human-built environment.

And today, architects and biologists

are working together

to explore smart building design

that will create

healthy buildings for us.

We spend an extraordinary amount of time

in buildings

that are extremely controlled environments,

like this building here --

environments that have mechanical ventilation systems

that include filtering,

heating and air conditioning.

Given the amount of time that we spend indoors,

it's important to understand

how this affects our health.

At the Biology and the Built Environment Center,

we carried out a study in a hospital

where we sampled air

and pulled the DNA

out of microbes in the air.

And we looked at three different types of rooms.

We looked at rooms that were mechanically ventilated,

which are the data points in the blue.

We looked at rooms that were naturally ventilated,

where the hospital let us turn off the mechanical ventilation

in a wing of the building

and pry open the windows

that were no longer operable,

but they made them operable for our study.

And we also sampled the outdoor air.

If you look at the x-axis of this graph,

you'll see that what we commonly want to do --

which is keeping the outdoors out --

we accomplished that with mechanical ventilation.

So if you look at the green data points,

which is air that's outside,

you'll see that there's a large amount of microbial diversity,

or variety of microbial types.

But if you look at the blue data points,

which is mechanically ventilated air,

it's not as diverse.

But being less diverse

is not necessarily good for our health.

If you look at the y-axis of this graph,

you'll see that, in the mechanically ventilated air,

you have a higher probability

of encountering a potential pathogen,

or germ,

than if you're outdoors.

So to understand why this was the case,

we took our data

and put it into an ordination diagram,

which is a statistical map

that tells you something

about how related the microbial communities are

in the different samples.

The data points that are closer together

have microbial communities that are more similar

than data points that are far apart.

And the first things that you can see from this graph

is, if you look at the blue data points,

which are the mechanically ventilated air,

they're not simply a subset of the green data points,

which are the outdoor air.

What we've found is that mechanically ventilated air

looks like humans.

It has microbes on it

that are commonly associated with our skin

and with our mouth, our spit.

And this is because

we're all constantly shedding microbes.

So all of you right now

are sharing your microbes with one another.

And when you're outdoors,

that type of air has microbes

that are commonly associated with plant leaves and with dirt.

Why does this matter?

It matters because the health care industry

is the second most energy intensive industry

in the United States.

Hospitals use two and a half times

the amount of energy as office buildings.

And the model that we're working with

in hospitals,

and also with many, many different buildings,

is to keep the outdoors out.

And this model

may not necessarily be the best for our health.

And given the extraordinary amount

of nosocomial infections,

or hospital-acquired infections,

this is a clue that it's a good time

to reconsider our current practices.

So just as we manage national parks,

where we promote the growth of some species

and we inhibit the growth of others,

we're working towards thinking about buildings

using an ecosystem framework

where we can promote the kinds of microbes

that we want to have indoors.

I've heard somebody say

that you're as healthy as your gut.

And for this reason, many people eat probiotic yogurt

so they can promote a healthy gut flora.

And what we ultimately want to do

is to be able to use this concept

to promote a healthy group

of microorganisms inside.

Thank you.

(Applause)