SARS-CoV-2 Coronavirus Can Remain Infectious And Active On Face Mask And PPE Equipment For As Long As 5 to 8 Days

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The SARS-CoV-2 coronavirus stability and infection persistence has been studied on different surfaces, but scarce data exist related to personal protective equipment (PPE), moreover using realist viral loads for infection.

Due to the importance for adequate PPE management to avoid risk of virus infection, RNA stability was evaluated on PPE.
 
The study team focused on the persistence of SARS-CoV-2 infection and detection of genomic RNA in PPE (gowns and face masks) which were determined by in-vitro assays and RT-qPCR, respectively.

Samples were infected with a clinical sample positive for SARS-CoV-2 (Clin-Inf), and with a heat-inactivated SARS-CoV-2 strain sample (Str-Inf) as a control.
 
Alarmingly, the study finding showed that PPE samples infected with Clin-Inf were positive for the 3 viral genes (N, S and ORF1ab) on gowns up to 5 days post-infection, whereas these overall genes were detected up to 30 days in the case of face masks.
 
However, gowns and FFP2 masks samples contaminated with Clin-Inf showed a cytopathic effect over VERO cells up to 5–7 days post-infection.
 
The study findings showed that SARS-CoV-2 RNA was detected on different PPE materials for 5 to 30 days, but PPE contaminated with the virus was infectious up to 5–7 days.
 
The study findings demonstrate the need to improve PPE management and to formulate strategies to introduce viricidal compounds in PPE fabrics.
 
The study findings were published in the peer reviewed journal: BMC Infectious Diseases. https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-021-06861-7

The in vitro assays data support that PPE materials (gowns and masks) infected with a clinical sample positive for SARS-CoV-2 maintained its infectiveness up to 5–7 days post-infection. This is accordance to the 7 days previously described for surgical masks and could have practical implications. https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(20)30003-3/fulltext


Discussion

In this study, the persistence of SARS-CoV-2 infection and the detection of genomic RNA of SARS-CoV-2 on PPE such as gowns and face masks were evaluated.

Our in vitro assays data support that PPE materials (gowns and masks) infected with a clinical sample positive for SARS-CoV-2 maintained its infectiveness up to 5–7 days post-infection. This is accordance to the 7 days previously described for surgical masks [7] and could have practical implications.

On the other hand, we detected viral genes in different types of PPE for up to 5 days after viral infection, and in some cases viral RNA was detected after 30 days (Table 2).

Moreover, gown samples produced lower virus survival since the 3 viral genes were detected up to 5 days in both types of infection, with the genomic RNA from the heat-inactivated virus strain or with the clinical sample positive for SARS-CoV-2.

In the case of face masks, the viral RNA stability was shown up to 15 days in the case of the control of genomic RNA viral strain and for 30 days when infected with the clinical sample positive for SARS-CoV-2.

SARS-CoV-2 has already been reported to persist on different surfaces for several days [4, 8, 9]. The limitation of most of these studies is that virus infections were performed with high viral loads resembling unrealistic scenarios [10]. In this study, we used a viral load corresponding to a more realistic situation, by using a human nasopharyngeal sample positive for SARS-CoV-2 to infect different PPEs samples.

Previously reported viral loads of SARS-CoV-2 in clinical samples ranged from a median of 7.99 × 104 copies per mL in throat samples and 7.52 × 105 in sputum samples post onset to overall higher values > 1 × 106 copies per mL of the viral load early after onset [11].

Therefore, to accurately quantify the expected viral copy number of a clinical sample, a reliable and robust standard curve must be established. In our study, a nasopharyngeal sample was quantified by qPCR using a reliable standard curve performed with an appropriate reference material. From the resulting data, we decided to use a viral load concentration within approximate ranges (104 viral copies) for infecting PPE samples trying to resemble a real situation.

The observed differences between the persistence of viral detection when infecting with a SARS-CoV-2 positive clinical sample (Clin-Inf) or viral RNA from a heat-inactivated SARS-CoV-2 strain (Str-Inf) used as a control, are consistent to their different nature.

The virus contained in the nasopharyngeal cells presents its protective capsid which preserves its genomic material for a longer period, as it was observed in our study. Whereas the capsid of the heat inactivated commercial strain has functional and structural alterations that turn the virus non-infectious but more labile. Virus persistence was determined by the detection of viral RNA in different PPE materials.

Finally, we could observe that the composition material of face masks (FPP2 type), seems to be more suitable for virus stability probably due to its more porous nature, when compared to gown´s fabric [12]. Our results demonstrate that virus infectious viability on different surfaces should not only be tested by using molecular techniques, since genes could be detected longer than viral infective viability.

Conclusions

PPE materials contaminated with SARS-CoV-2 remain infective between 5 to 7 days. Viral genomic RNA was detected in different PPE materials for 5 to 30 days in the case of face masks. We believe that these findings demonstrate the need of improving PPE fabric composition and to evaluate the addition of viricidal compounds to them.

The responsible management of these PPE is crucial to avoid SARS-CoV-2 infection by contact of these items even many days after they are removed.

Table 2 SARS-CoV-2 gene detection in PPE samples infected with SARS-CoV-2 positive human clinical sample (Clin-Inf)

From: Persistence of SARS-CoV-2 infection on personal protective equipment (PPE)

  1. aCt: Cycle threshold in relation to the number of cycles required for the fluorescent marked amplification to cross the threshold in the RT-qPCR reaction. Lower Ct values indicates higher viral load. Ct-values ≤ 37.0 were considered as positive

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