We've all been told to cough and sneeze into our elbow and keep a distance from others, but can those with COVID-19 pass it onto others just by breathing and talking? In other words, can it become airborne?

There's been a lot of talk about this the past week—but it's a complicated question, and the answer depends on who you ask.

When a sick person coughs or sneezes, large droplets fly through the air and can infect people nearby (usually under a metre or so but sometimes across much larger distances).

These are called respiratory droplets, and this is how experts think most people are getting sick with COVID-19.

Due to the droplets' relatively large size, greater than 5 micrometres, they usually don't travel very far, and they don't stay in the air too long.

But that's not the only type of droplet. Much smaller droplets can also be produced when we sneeze and cough, as well as when we talk and breathe. These are called bioaerosols, and they can travel a lot further, and can stay airborne for a longer period of time.

But can you get COVID-19 from these bioaerosols?

The answer has important implications for healthcare workers, and others working in close proximity to those who are sick, and researchers are scrambling to work it out.

One way to test this is to take samples from the air itself and see whether there are any viral RNA particles floating around. In one preprint article, researchers found SARS-CoV-2 particles in both air and surface samples taken in isolation rooms where COVID-19 patients had been staying.

But another study, published in Infection Control & Hospital Epidemiology found no viral particles when collecting air samples just 10 centimetres (4 inches) from COVID-19 patients' chins. It's worth nothing that this paper only looked at eight air samples.

So what does all of this mean? The US National Research Council last week told government officials that it is possible bioaerosols are partly to blame for the virus's ability to rapidly spread.

"Currently available research supports the possibility that SARS-CoV-2 could be spread via bioaerosols generated directly by patients' exhalation," writes Harvey V. Fineberg from the Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats, who was the author of the letter.

But he then explains that we need to be cautious with the results so far.

Many of the studies being referred to have used past respiratory viruses like SARS and the flu, which may not work the same way as COVID-19 does, and just because a study finds viral RNA in the air doesn't necessarily mean that there was ever enough there to make someone sick.

"Nevertheless, the presence of viral RNA in air droplets and aerosols indicates the possibility of viral transmission via these routes," he adds.

The World Health Organisation (WHO) has also released guidelines on this, saying that airborne bioaerosol transmission of COVID-19 has not been reported, except in very specific circumstances.

"In the context of COVID-19, airborne transmission may be possible in specific circumstances and settings in which procedures or support treatments that generate aerosols are performed," they write.

This includes things like removing a patient from a ventilator or manual ventilation.

"To date, some scientific publications provide initial evidence on whether the COVID-19 virus can be detected in the air and thus, some news outlets have suggested that there has been airborne transmission. These initial findings need to be interpreted carefully."

In a rapidly evolving crisis, it's best to listen to the health advice of organisations like WHO, and although the research is still being collated, it doesn't mean we need to panic.

Keeping up physical distancing and isolating where possible is still the best way to avoid getting sick—either from respiratory droplets or bioaerosols.

Plus, people such as health care workers in high risk situations are already advised to use masks to protect themselves from those that are sick.

The best thing you can do is stay home where possible, keep an eye on new guidelines as they emerge, and look out for each other. 

—Jacinta Bowler