A Covid test as easy as breathing
People with diabetes, for example, may have fruity or sweet breath. The smell is caused by ketones, chemicals produced when the body begins to burn fat instead of glucose for energy, a metabolic state known as ketosis.
“The idea that exhaled air might contain diagnostic potential has been around for some time,” Dr Davis said. “There are reports in ancient Greek and ancient Chinese medical education texts that refer to a physician’s use of smell as a means to help guide clinical practice.”
Modern technologies can detect more subtle chemical changes, and machine learning algorithms can identify patterns in breath samples from people with certain diseases. In recent years, scientists have used these methods to identify unique “fingerprints” for lung cancer, liver disease, tuberculosis, asthma, inflammatory bowel disease, and other conditions. (Dr Davis and his colleagues even used VOC profiles to distinguish cells that had been infected with different strains of influenza.)
Before the Covid hit, Breathomix had developed an electronic nose to detect several other respiratory illnesses. “We train our system, ‘Okay, that’s how asthma smells, like lung cancer smells,” said Rianne de Vries, chief technology and scientific officer for the company. “So it’s about creating a big database and finding patterns in big data. “
Last year, the company – and many other researchers in the field – pivoted and began trying to identify a respiratory footprint for Covid-19. In the initial outbreak of the virus in spring 2020, for example, British and German researchers collected breath samples from 98 people who presented to hospitals with respiratory symptoms. (Participants were asked to breathe out into a disposable tube; the researchers then used a syringe to extract a sample from their breath.)
Thirty-one of the patients were found to have Covid, while the rest had a variety of diagnoses, including asthma, bacterial pneumonia or heart failure, the researchers reported. Breath samples from people with Covid-19 showed higher levels of aldehydes, compounds produced when cells or tissues are damaged by inflammation, and ketones, consistent with research suggesting the virus can damage the pancreas and cause ketosis.
Covid patients also had lower methanol levels, which could be a sign that the virus had inflamed the gastrointestinal system or killed the methanol-producing bacteria that live there. These combined breathing changes “give us a Covid-19 signal,” said Dr. Thomas, co-author of the study.