Studying splashes to learn more about how disease spreads

Lydia Bourouiba, an applied mathematician at the Massachusetts Institute of Technology, studies sneezes at a level of detail most of us have never imagined — under bright lights, using advanced imaging technology.

“When you zoom in, parts of the clouds look like snowflakes,” she explains in Science Friday’s new video, “Breakthrough: Connecting the Drops.”

“It’s really beautiful.”

Beautiful they may be, but Bourouiba’s research has modeled how droplets — sent into the air by our sneezes, for example, or the flush of a toilet — can also efficiently spread bacteria and viruses. “So what we’re trying to do is not just have empirical data,” she explains.

“So actually, we developed different image processing algorithms to try to extract the data in terms of droplet sizes, temporal evolution — so with time and space, where is all this going,” she says, ”but then also develop mathematical models, basically fluid dynamics models based on equations, to understand better, ‘How could we more efficiently target these processes to … minimize them?’”

She explains that when we sneeze, we emit a fast-moving cloud of droplets. The warm, moist cloud travels up and away from us — straight towards the ceiling vents in many modern buildings. It gets ickier: “Most ventilation systems indoors do not have filters between rooms,” she says. “So whatever is remaining in that cloud that reaches the ceiling can be redistributed.”

And when it comes to toilets, Bourouiba says that a design choice made in many public bathrooms for sanitation and energy efficiency — a lidless toilet with a high-pressure flush — can actually more effectively send droplets into the air.

“And in those cases, those choices for not having a lid, for example, were taken to minimize biofilm formation — so contamination and attachment of other type of organisms on surfaces,” she explains. But in her research, she’s wondered whether high-pressure flushes could be linked to the lingering presence of certain disease strains in hospitals — the bugs “that individuals sometimes come in without and leave with.”

“And indeed, it was quite surprising to see how much of the droplets were much smaller than what I expected initially,” she says, meaning they behave like the small droplets emitted by sneezes and coughs. “They can travel further, linger in the rooms, because they're not going to really settle on surfaces to be cleaned with the current surface-sanitizing protocols.”

The thought is enough to make any of us hold it for the safe haven of our own bathrooms. Indeed, Bourouiba says, our home toilets tend to be rotationally flushing models that minimize spray. “And in fact, most households also have lids, so the advice would be to lower that lid and make sure that it's cleaned, obviously, regularly for minimizing biofilms.”

“But the real concerns are in these public spaces and common spaces, where for energy efficiency, water efficiency and turnaround efficiency, we really need to have that optimal high-pressure flush.”

So for now, she’s focusing on ways to make places like hospitals safer from spatter. She thinks there are answers in physics — fluid dynamics models that help researchers target and minimize high-spatter situations.

“There’s a lot of simple questions to be asked about, ‘Is this design of the hospitals optimized to minimize basic transmission between patients?’” she says in the Science Friday video. “Now we can actually start revisiting our ventilation systems, and also the way that wards are designed in times of emergency when you have to put something together very quickly.”

This article is based on an interview that aired on PRI's Science Friday.