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Viral load dynamics and disease severity in patients infected with SARS-CoV-2 in Zhejiang province, China, January-March 2020: retrospective cohort study

BMJ 2020; 369 doi: https://doi.org/10.1136/bmj.m1443 (Published 21 April 2020) Cite this as: BMJ 2020;369:m1443

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Persistence of viral RNA in stool samples from patients recovering from covid-19

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Measuring airborne COVID-19 virions load predicts infection spread

Dear Editor,

We greatly appreciated the paper by Zheng et al. demonstrating that nowadays it is possible to detect COVID-19 virions and to measure their load in different biological samples: interestingly these data correlate with the persistence and severity of the disease [1].

For analogy, the demonstrated presence of COVID-19 virions in the atmosphere could constitute an indicator of persistence and of further epidemic spread. It is well known that virions, when incorporated in airborne nanoparticles, become subject to many physical processes, such as Brownian diffusion, coagulation with other particles, thermophoresis, diffusiophoresis, electrostatic or aerodynamic capture, that increase their survival and replication power, and regulate their propagation, penetration inside the human respiratory tract and adhesion to the encountered surfaces.

The same physical processes are involved in their removal from the atmosphere in course of precipitations [2,3]. Therefore, it would be useful to search the presence of COVID-19 virions also in the atmospheric aerosol particulate, indoor and outdoor, by physical methods, adequately adapted. Scanning electron microscopy can provide qualitative data, while the viral load can be differently calculated: by flow virometry or by measuring directly SARS-CoV-2 RNA content extracted through a polymerase chain reaction, otherwise after inoculation of atmospheric particles in cells cultures apt to viruses isolation [1,4,5].

These data could be usefully integrated with the clinical ones, in order to monitor the persistency or the ongoing epidemic spread, with the inherent risk of people infection, while acknowledging that the onset of a particular disease represents the final result of many other concurrent causes, such as immunodepression, co-morbidity and age.

Franco Prodi°, Luca Roncati*, Antonio Manenti*

° Italian Academy of Sciences, Rome, Italy
* University Hospital of Modena, Modena, Italy

Corresponding author: Prof. A. Manenti, Polyclinic Hospital, Largo del Pozzo 71 - 41124 Modena, Italy
E-mail: antonio.manenti@unimore.it

References
1. Zheng S, Fan J, Yu F, et al. Viral load dynamics and disease severity in patients infected with SARS-CoV-2 in Zhejiang province, China, January-March 2020: retrospective cohort study. BMJ 2020;369:m1443.
2. Pan M, Lednicky JA, Wu CY. Collection, particle sizing and detection of airborne viruses. J Appl Microbiol 2019;127:1596‐611.
3. Prodi F, Tampieri F. The removal of particulate matter from the atmosphere: the physical mechanisms. PAGEOPH 1982;20:286-325.
4. Morawska L, Cao J. Airborne transmission of SARS-CoV-2: the world should face the reality. Environ Int 2020;139:105730.
5. Zamora JLR, Aguilar HC. Flow virometry as a tool to study viruses. Methods 2018;134-135:87‐97.

Competing interests: No competing interests

30 April 2020
Antonio Manenti
University professor
Franco Prodi, Luca Roncati (University Hospital of Modena, Modena, Italy)
University of Modena and Reggio Emilia (Italy)
Polyclinic Hospital, Largo del Pozzo 71 - 41124 Modena, Italy