Non-invasive adapted N-95 mask sampling captures variation in viral particles expelled by COVID-19 patients: Implications in understanding SARS-CoV2 transmission

Abstract

Infectious respiratory particles expelled by SARS-CoV-2 positive patients are attributed to be the key driver of COVID-19 transmission. Understanding how and by whom the virus is transmitted can help implement better disease control strategies. Here we have described the use of a noninvasive mask sampling method to detect and quantify SARS-CoV-2 RNA in respiratory particles expelled by COVID-19 patients and discussed its relationship to transmission risk. Respiratory particles of 31 symptomatic SARS-CoV-2 positive patients and 31 asymptomatic healthy volunteers were captured on N-95 masks layered with a gelatin membrane in a 30-minute process that involved talking/reading, coughing, and tidal breathing. SARS-CoV-2 viral RNA was detected and quantified using rRT-PCR in the mask and in concomitantly collected nasopharyngeal swab (NPS) samples. The data were analyzed with respect to patient demographics and clinical presentation. Thirteen of 31(41.9%) patients showed SARS-COV-2 positivity in both the mask and NPS samples, while 16 patients were mask negative but NPS positive. Two patients were both mask and NPS negative. All healthy volunteers except one were mask and NPS negative. The mask positive patients had significantly lower NPS Ct value (26) compared to mask negative patients (30.5) and were more likely to be rapid antigen test positive. The mask positive patients could be further grouped into low emitters (expelling <100 viral copies) and high emitters (expelling >1000 viral copies). The study presents evidence for variation in emission of SARS-CoV-2 virus particles by COVID-19 patients reflecting differences in infectivity and transmission risk among individuals. The results conform to reported secondary infection rates and transmission and also suggest that mask sampling could be explored as an effective tool to assess individual transmission risks, at different time points and during different activities.

Fig 1. Viral copies and Ct values in mask and NPS samples.

(A) SARS-CoV-2 viral copies expelled in 30 minutes by the mask positive patients. Data represented as median with IQR with the blue line indicating the median viral copies. (B) The distribution of Ct values from mask and NPS samples. The Ct value of the E gene in mask samples (blue) at sampling, the Ct value of the N gene in mask positive samples (red) and mask negative samples (green) at sampling, and Ct value of the N gene in patient samples at diagnosis. The mask E gene Ct values showed two distinct groups of samples with low Ct values (black bracket) and samples with high Ct values (blue bracket). No distinct groups were seen in the N gene Ct values of NPS samples at enrollment or diagnosis. Data represented as median with IQR with the thick black line indicating the median Ct value. (C) Scatter plot with the Ct values of The E gene in mask and N gene in NPS patient samples on the Y-axis and days from onset of first symptoms of each patient on the X-axis. The mask E gene Ct values represented as blue triangles, the NPS N gene Ct values in mask positive patients, and mask negative patients represented as red dots and green squares respectively. The box encloses all the Ct value of the mask and NPS patient samples up to 5 days from the first onset of symptoms. The dotted line represents the Ct value when 1000 viral copies are expelled by the patients in 30 minutes. Abbreviations Ct- Cycle Threshold, NPS-Nasopharyngeal Swab.