According to a study, transmission of infectious SARS-CoV-2 from floating objects is possible, but unlikely in real-life scenarios.

Fomites are droplet-contaminated surfaces that may play a role in the transmission of the 2019 coronavirus disease (COVID-19). At the beginning of the pandemic, washing items entering the home became popular to eliminate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the ability of fomites to contribute to the spread of disease remains controversial, and most researchers have begun to downplay the likelihood of fomite infection. In a study published in The Journal of Infectious Diseasesresearchers studied the role of fomites in the transmission of SARS-CoV-2.

Study: Low risk of SARS-CoV-2 transmission via fomites – an observational clinical study in highly contagious COVID-19 patients. Image Credit: David Pereiras/Shutterstock

About the research and the results

To conduct their study, the researchers gathered people treated in hospital with a confirmed SARS-CoV-2 infection and a high viral load. They were then asked to cough vigorously into nine steel racks and wet another nine racks with their mouths. These media were then placed in containers and transported on ice to a university lab, where they were used to inoculate VeroE6 cells.

Fifteen people between the ages of 39 and 89 were recruited, all of whom had risk factors for severe COVID-19. Three patients had two risk factors, while most of the other subjects had between 3 and 6 risk factors. On the day of the study, 60% of the people recruited had only mild symptoms and only seven patients required nasal oxygen administration. No individual was vaccinated. During follow-up studies, ten patients experienced worsening clinical symptoms, two patients died from COVID-19, and one patient died from COVID-19.

Overall, patients with higher levels of lactate dehydrogenase, leukocytes, and C-reactive protein at admission were significantly correlated with more severe COVID-19 infection. No correlation was found between the severity of COVID-19 and other known predictors, including age, alanine aminotransferase, aspartate aminotransferase, procalcitonin, or D-dimers.

The viral load of all patients was determined by reverse transcription polymerase chain reaction (RT-PCR) analysis of nasopharyngeal and oropharyngeal swabs prior to sampling. The variants present included wild-type in 10 patients, alpha-type in four patients, and beta-type in one patient.

The pangolin tool was used for deep sequencing to confirm lineage assignment for fourteen samples, with variant patterns identified by examination of the spike domain. Two samples were excluded from the study due to contamination. All other samples showed clear detection of viral RNA, and after inoculation with the swabs, the viral load in the cells was between 2×10^1 and 2×10^9 RNA copies/50ng. Some patients had significantly lower viral loads and had no Pap smears resulting in a productive viral infection.

Steel racks contaminated by wetting with saliva resulted in visible cytopathic effect (indicating viral infection) and detectable viral RNA in cells in six of 13 cases. Although there was no apparent cytopathic effect in patients six and ten, viral RNA was still detected in cells and supernatant. Five of the 13 steel grades contain a recoverable infectious virus. In some patients, the infectious virus could be recovered 240 minutes after incubation. Viral RNA could be detected in five of the cell samples from the sample carriers who had infected the patients with a strong cough, but no cytopathic effects could be observed.

The small population studied makes it difficult to draw strong conclusions from this study. In a study of disease transmission, taking only hospitalized people with a high viral load significantly reduces the scope of the study. The lack of correlation between severe COVID-19 and age suggests that the limited study size may significantly reduce the statistical strength of the study, as larger cohort studies have yielded mixed results.

In addition, no statistical analysis is reported on the difference between steel racks in which patients coughed and steel racks moistened with saliva – and since only one additional rack contained viral RNA, the difference does not appear likely to be significant. The difference in the visible cytopathic effect is more revealing, but it is difficult to quantify reliably in the absence of figures on this effect. Also the presence of contamination in multiple samples is not encouraging.

Conclusion

The authors conclude that their study provides evidence that fomites are not as critical in disease transmission as they previously believed, and also demonstrates that infectious SARS-CoV-2 virions from some fomites can be recovered for a relatively short period of time after infection. with large volumes of saliva. They advise following general hygiene practices recommended by almost all governments during the pandemic to reduce the risk of surface contamination and viral transmission.

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