Sir,
Narita et al. demonstrated strong germicidal effects of 254-nm and 222-nm ultraviolet C (UVC) light against various suspensions of pathogenic bacteria, yeasts, an enveloped virus (influenza A) and a non-enveloped virus [feline calcivirus (FCV), a surrogate of the human norovirus] [1]. UVC light strongly inactivated influenza A, but inactivation was less pronounced on the non-enveloped or naked FCV. Dried inocula of other naked viruses have been shown to be infectious for weeks, whereas the dried inocula of the enveloped viruses influenza A and herpes simplex type 1 were infectious for <5 days [2]. This study explored the germicidal impact of different amounts of far-UVC irradiation (222-nm) against dried inocula of a naked human rhinovirus (HRV type 37) and an enveloped human coronavirus (HCoV 229E) on a glass carrier.
Study parameters were HRV type 37 (ATCC, VR-1147, Manassas, VA, USA), MRC-5 human embryonic lung fibroblasts (ATCC), temperature (21.2–22.0oC), humidity (15.0–19.5%), organic soil load (1% fetal bovine serum), and test medium (Minimal Essential Medium; Life Technologies, Carlsbad, CA, USA) supplemented with 10% [v/v] heat-inactivated fetal bovine serum (Life Technologies), 100 units/mL penicillin (Sigma-Aldrich, St. Louis, MO, USA), 10 μg/mL gentamicin (Thermo Fisher, Ward Hill, MA, USA) and 2.5 μg/mL amphotericin B (Sigma-Aldrich). The study parameters for HCoV 229E (ATTC, VR-740) were the same except WI-38 human lung cells (ATCC) were the indicator cell culture, and the fetal bovine serum of the test medium was 2% (v/v). Test and control carriers were run in duplicate. Treated carriers were placed 101.6 cm directly below a 250-W far-UVC excimer lamp (Sterilray Luminaire, Somersworth, NH, USA) and irradiated at three different dosages (Table I ). Dosages were measured using the ILT2400 radiometer (International Light Technologies, Peabody, MA, USA). Following exposure, test carriers were resuspended, serial 10-fold dilutions were made, and dilutions were assayed for infectivity [median tissue culture infectious dose (TCID50)]. Control carriers were exposed to ambient air for the same amounts of time as treated carriers. A test-substance cytotoxicity control was run concurrently and exposed to ambient air for 243 s. Infectivity of controls was determined using the same method as test carriers.
Table I.
Virucidal effect of 222-nm ultraviolet C (UVC) light on dried inocula of human rhinovirus (HRV) type 37 and human coronavirus (HCoV) 229E on glass carriers
| Virus | Control |
Treatment |
||||
|---|---|---|---|---|---|---|
| Exposure to ambient air (s) | Viral titre (TCID50/100 μL)a | Exposure to 222-nm UVC (mJ/cm2) | Viral titre (TCID50/100 μL) | Log10 reduction | Percent reduction | |
| HRV type 37 | 11 | 1 x 104.82 | 0.93 | 1 x 104.57 | 0.25 | 43.80% |
| 34 | 1 x 104.64 | 2.72 | 1 x 103.64 | 1.00 | 90.00% | |
| 241 | 1 x 104.50 | 19.35 | 1 x 102.14 | 2.36 | 99.60% | |
| HCoV 229E | 12 | 1 x 104.50 | 0.95 | 1 x 103.39 | 1.11 | 92.20% |
| 33 | 1 x 104.32 | 2.69 | 1 x 103.07 | 1.25 | 94.40% | |
| 243 | 1 x 104.64 | 19.42 | 1 x 101.32 | 3.32 | 99.95% | |
Viral titres are mean values of samples run in duplicate.
Stock solutions for HRV type 37 and HCoV 229E contained 1.0 x 105.5 TCID50/100 μL and 1.0 x 105.0 TCID50/100 μL, respectively. The cytotoxicity control for RHV type 37 and HCoV 229E contained ≤1 x 100.50 TCID50/100 μL.
Dried inocula of HRV and HCoV on glass carriers were inactivated increasingly in response to higher dosages of 222-nm UVC light (Table I); however, the naked HRV may be more stable at low dosages (i.e. 0.9 mJ/cm2). HRV accounts for 50–66% of common colds, and HCoV is the second leading cause of this illness [3,4], resulting in billions of indirect and direct costs each year [5]. Paradoxically, the common cold may protect people from contracting coronavirus disease 2019 [6] and influenza [7] through viral competition. Although excimer far-UVC lamps that emit 222-nm light are now commercially available and can be a powerful prophylactic against HRV and HCoV, additional research is needed to optimize the use of 222-nm UVC light for the best health outcomes.
Acknowledgements
The authors wish to thank Matthew Sathe, Thomas Breyen and their teams at Element Materials Technology Minneapolis–Eagan Inc. (Eagan, MN, USA) for implementing the protocol, analysing data and writing the methods. The authors also wish to thank Jessica Knight for help with editing and manuscript preparation.
Conflict of interest statement
None declared.
Funding sources
None.
References
- 1.Narita K., Asano K., Naito K., Ohashi H., Sasaki M., Morimoto Y. Ultraviolet C light with wavelength of 222 nm inactivates a wide spectrum of microbial pathogens. J Hosp Infect. 2020;105:459–467. doi: 10.1016/j.jhin.2020.03.030. [DOI] [PubMed] [Google Scholar]
- 2.Firquet S., Beaujard S., Lobert P.-E., Sane F., Caloone D., Izard D. Survival of enveloped and non-enveloped viruses on inanimate surfaces. Microbes Environ. 2015;30:140–144. doi: 10.1264/jsme2.ME14145. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Arruda E., Pitkäranta A., Witek T.J., Doyle C.A., Hayden F.G. Frequency and natural history of rhinovirus infections in adults during autumn. J Clin Microbiol. 1997;35:2864–2868. doi: 10.1128/jcm.35.11.2864-2868.1997. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Mäkelä M.J., Puhakka T., Ruuskanen O., Leinonen M., Saikku P., Kimpimäki M. Viruses and bacteria in the etiology of the common cold. J Clin Microbiol. 1998;36:539–542. doi: 10.1128/jcm.36.2.539-542.1998. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Fendrick A.M., Monto A.S., Nightengale B., Sarnes M. The economic burden of non-influenza-related viral respiratory tract infection in the United States. Arch Intern Med. 2003;163:487. doi: 10.1001/archinte.163.4.487. [DOI] [PubMed] [Google Scholar]
- 6.Aran D., Beachler D.C., Lanes S., Overhage J.M. Prior presumed coronavirus infection reduces COVID-19 risk: a cohort study. J Infect. 2020;81:923–930. doi: 10.1016/j.jinf.2020.10.023. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Greer R.M., McErlean P., Arden K.E., Faux C.E., Nitsche A., Lambert S.B. Do rhinoviruses reduce the probability of viral co-detection during acute respiratory tract infections? J Clin Virol. 2009;45:10–15. doi: 10.1016/j.jcv.2009.03.008. [DOI] [PMC free article] [PubMed] [Google Scholar]