In just five months, the COVID-19 paralyzed huge cities, confined billions to their homes, and brought economic activity to a standstill in much of the world. Tens of thousands of patients became critically ill, overwhelming healthcare facilities. Even as many recovered and were ready to go home, a new study published in May 2020 on the preprint server medRxiv* reports that a significant number of patients ready to go home still have virus particles in their exhaled breath.
Within hospitals and quarantine centers for COVID-19 patients, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been found to be contaminating the air, surfaces that are often touched, and the floors. Many medical staff in such centers have been infected and even died as a result.
An ongoing challenge in the current day is making sure that patients are discharged in a timely fashion to optimize the use of healthcare resources, while also taking care to minimize the spread of the virus from these discharged patients. The most commonly used test is PCR on throat and nose swabs, sometimes with chest CT scans. This has sometimes resulted in a re-test showing a previously negative patient to become positive again.
The Study: Finding the Virus in the Environment
The current study is aimed at understanding how the virus can contaminate surfaces and air within a COVID-19 hospital, and to test exhaled breath samples from recovering patients for the presence of SARS-CoV-2.
The study involves ten recovering patients, all more than 70 years of age, and with negative throat swabs at the time of testing the exhaled breath. The breath tests were done 14 or more days from the first symptom. They had had IgG tests about 4-7 days before the breath test.
In two patients who were being tested about 5-6 weeks from the first symptom, the exhaled breath turned out to be positive for COVID-19 despite negative throat swabs on repeated occasions. The average emission rate was about 1400 copies/minute. Overall, one in five of the recovering patients had positive exhaled breath samples.
There were 318 swabs taken from various surfaces, of which four were positive for the virus. Two were from surfaces often touched by medical staff, two from supply delivery windows, and the shoe cabinets. The most frequently touched surfaces like cell phones, door handles, patients’ hands, or masks failed to return even a single positive sample out of the 158 collected samples.
Patients whose masks tested negative also had negative exhaled breath samples. Similarly, samples from the hospital floor, clean areas, and other hospital areas were negative – 94 samples in all. The positive samples from surfaces thus amounted to only 1.3% of the samples.
The air samples were uniformly negative for the virus, even those from the intensive care unit (ICU), even with the six re-tested samples.
Virus Exhalation from Throat Swab-Negative Patients
The current findings are supported by another paper that reports positive bronchoalveolar lavage samples despite repeatedly negative throat swabs. This suggests that recovering patients could, in some cases, exhale the SARS-CoV-2 into their surroundings and continue to spread the virus to their surroundings.
When it is noted that the two patients who tested positive in this manner were ready for discharge, with negative throat swabs but positive exhaled air samples, the infection risk is obvious. It is thought that throat swabs and exhaled breath specimens could produce different results.
To improve the efficiency of diagnosis in such cases, throat swab testing could be supplemented by exhaled breath specimens, or chest CT scans, for instance. The current study failed to examine the viability or biological integrity of the virus in the breath samples. Still, an earlier study has shown that it can remain viable for up to 3 hours.
Aerosolized SARS-CoV-2 would be expected to be less viable than a breath-emitted virus, which would mean the latter would also be present in the air for at least this length of time, allowing viral transmission. Thus, it is essential to understand how COVID-19 patients can spread the virus through the air and for how long. The current study shows that in at least a fifth of cases, the present discharge protocol fails to ensure safety for those surrounding the patient.
Low Prevalence of Virus on Other Surfaces and in Air
The study also shows that surface spread is very low, surprising though this may appear, even in a high-risk environment. The reasons may include the lack of data on how the virus is emitted by these patients, when, where, and how often. Secondly, virus emission may occur only during certain activities such as coughing, sneezing, or talking, or respiratory therapy, which is hard to pinpoint and may have occurred at other times before the sample was taken.
Thirdly, the frequent use of disinfectants in the hospital setting may have inactivated the virus and its nucleic acid. The use of a mask by every COVID-19 patient while in the hospital could also have limited virus release from the lungs into the air.
Finally, the open-window policy to facilitate natural air ventilation would ensure the airborne virus to be diluted rapidly. The use of the RT-PCR method could have led to missing the virus because of its inability to detect less than 100 viral copies/ μL.
Perhaps as a result of all these factors, no medical staff in any of the four hospitals where the study was conducted reported any infection, and air samples were all negative. However, the researchers conclude, “While low infection risks were shown for surfaces and air in the evaluated hospitals, our data reveal a critical need to revisit current hospital discharge guidelines to minimize the public risk.”
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.