Several other studies have also detected unique chemical patterns in the breath of patients with Covid-19, and some devices claim impressive results. In one study of the SpiroNose, which included 4,510 participants, a team of Dutch researchers reported that the device correctly identified at least 98 percent of people who were infected with the virus, even in a group of asymptomatic participants. (The study, which included researchers from Breathomix, has not yet been peer-reviewed.)
But the SpiroNose had a relatively high rate of false positives, the study found. Because of this problem, the device does not provide consumers with a definitive diagnosis; the results either come back negative or inconclusive, in which case a standard P.C.R. test is administered.
Dozens of testing sites in the Netherlands are now using the machine, Ms. de Vries said, but there have been some hiccups. In May, Science reported that Amsterdam’s public health authorities suspended use of the SpiroNose after 25 false negatives. Officials later determined that user error was largely responsible, and SpiroNose screening has resumed, Ms. de Vries said.
Other groups are working on their own breathalyzers. Researchers at the Children’s Hospital of Philadelphia, who have identified a breathprint of Covid in children, are now trying to identify breath markers of a rare but dangerous complication of the disease, known as multi-system inflammatory syndrome in children (MIS-C).
“The clinicians on the front line, they’re really struggling with which children we need to worry most about,” said Dr. Audrey Odom John, an infectious disease specialist at Children’s Hospital of Philadelphia, who is leading the research.
In addition to studying the V.O.C.s emitted by Covid patients, Dr. Davis and her colleagues are analyzing what is known as exhaled breath condensate, a concentrated solution of the tiny droplets of fluid, or aerosols, that are present in breath. These aerosols contain all sorts of complex biological molecules, including proteins, peptides, antibodies and inflammatory markers.