Icon: enlarge
Nursing staff in an intensive care unit with Covid 19 patients in Switzerland: How can we stop the pandemic?
Photo: Gaetan Bally / dpa
Corona tests have so far been rather uncomfortable: a swab is inserted deep into the throat, sometimes even through the nose.
This is especially bad for many children, but adults too often struggle with gag reflex.
For some time, research has therefore been carried out on other tests that are easier to carry out and, above all, more pleasant.
Researchers from the Dortmund Clinic and the University of Edinburgh have now investigated to what extent the air we breathe is suitable as sample material for detecting infection.
When it comes to breath tests, one thinks first of all of the small devices that the police like to pull out during traffic checks.
Blow in once vigorously and within seconds the blood alcohol level appears on the display.
The idea of being able to "take corona infected people out of circulation" in a similar way sounds tempting.
Rapid tests are often discussed, which should filter out the super spreaders at the entrance to concerts or football games so that major events can be possible again.
Unfortunately, the corona breath tests are not that simple.
For their investigations, the two research teams independently tested symptomatic patients who presented to the clinic because of suspected corona.
These had to breathe through a much larger tube than the potential traffic offenders.
Air was taken from their oral cavity with a simple syringe and fed into a device with a very complicated name: gas chromatography-ion mobility spectrometer, GC-IMS for short.
A PCR test was also carried out on the patients in parallel.
Icon: enlarge
Test device for breath samples: gas chromatography ion mobility spectrometer
Photo: Frederik Hempel
Of the total of 89 people tested in Edinburgh and Dortmund, the PCR test was positive in 31.
The researchers compared the results with those of the breath tests: These had recognized around 80 percent of those infected as positive.
This means that about six patients were not recognized.
At a major event, it could be that out of 1000 visitors, around 200 corona positives walk around without being recognized as such.
Corona-typical substances in the air we breathe
It quickly becomes clear from the results that breath tests are unlikely to be the next big thing in pandemic control.
Nevertheless, one shouldn't write it off too quickly, says Olaf Holz, who researches non-invasive airway diagnostics at the Fraunhofer Institute.
"The study shows that there are apparently corona-related changes in the air we breathe that can be detected using a very sensitive method."
Now one still has to find out in a much larger number of patients how specific these substances really are for an infection with Sars-CoV-2.
Above all, the algorithm proposed in the study for detecting an infection in other patients must be validated.
Bernhard Schaaf, one of the authors of the study, agrees.
"In our study, we first wanted to see whether a breath test for Sars-CoV-2 is even possible," says Schaaf, director of the Dortmund Clinic.
"And that's it, we just have to find out which substances the test will respond to."
Because the breath test works very differently than the previous test procedures.
As a reminder, PCR and antigen tests look for the virus itself, more precisely for its proteins.
Antibody tests, in turn, look for specific antibodies that the body has made against the virus.
The breath test, on the other hand, does not want to find the virus itself, not even in aerosols, as one might initially assume.
It measures the body's response to the infection.
"When a person is infected, his body reacts to it," explains Schaaf.
"It then produces certain substances that are expelled, among other things, with the air we breathe."
The test examines the breath sample for a combination of different substances that would typically be formed in response to a corona infection.
“In the air you breathe, you can smell what your body is doing with the virus,” he says.
"About the fact that the metabolism was changed."
The next pandemic is sure to come
The study says that certain aldehydes, ketones and methanol have been identified that are typically formed when infected with Covid-19.
"The device calculates the concentration of these substances in the breath sample and can thus differentiate Covid-19 from other viral diseases," says Schaaf.
"But there are still not enough test subjects to get meaningful results. We have to test this on many more patients first."
Therefore, one is still very far from standing with the device in front of a football stadium.
The Braun company is also researching breath tests for Covid-19.
A feasibility study has been running in Munich since the end of September.
According to a spokeswoman, this study will examine breathing gas samples from a total of 100 participants who have symptoms of a respiratory disease.
PCR test results are also available from them.
The results are then to be compared in order to be able to make an initial statement as to whether specific differences can be found in the respiratory gas samples using the technology used by Braun.
According to the spokeswoman, results are not yet available.
The Fraunhofer expert Holz explains why you may encounter particular problems with respiratory diagnostics: "The air we breathe is affected by many factors, such as our environment or our lifestyle," he says.
"Intestinal bacteria, for example, produce a large number of substances that are released into the air we breathe. This means that a sample can also be changed by diet."
Nevertheless, the study gives initial indications that corona-specific changes can occur in the breath sample.
"But there is still a lot of work to be done, maybe so much that we won't have any more of it in this pandemic," says Holz.
"But the next pandemic will come, and then we'll be a little further."
Icon: The mirror
