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.
Highlights
One year into the COVID-19 pandemic, there have been over 100 million confirmed cases and over 2 million deaths due to COVID-19 worldwide
We demonstrate that our mask sampling method can be used to detect SARS-CoV-2 RNA generated by COVID-19 patients using real-time reverse transcriptase-polymerase chain reaction, and the cycle threshold (Ct) value can indicate the potential infectiousness of different patients [15]
Of the 31 previously confirmed COVID-19 patients, SARS-CoV-2 viral RNA was detected by reverse transcriptase-polymerase chain reaction (rRT-PCR) in 29 (93.54%) nasopharyngeal swab (NPS) samples while expelled SARS-CoV-2 virus was detected in mask samples of 13 patients (44.8% of contemporary NPS positive patients and 41.9% of 31 confirmed patients)
Summary
One year into the COVID-19 pandemic, there have been over 100 million confirmed cases and over 2 million deaths due to COVID-19 worldwide. The dispersion factor for COVID-19 has been estimated to be as low as 0.1 indicating that COVID-19 transmission is over-dispersed, which means a small number of infected individuals drive most of the spread [3]. Collecting nasopharyngeal or oropharyngeal specimens by inserting a swab may not correlate with the potential of the host to generate infectious respiratory particles, nor reflect different host activities that result in different transmission risks; singing and heavy breathing during exercising are thought to result in more infectious particles than speaking softly or quiet breathing [7,8]. There is a need for sampling methods that better reflect the transmission risk of infected individuals during different actions such as breathing, speaking, shouting or singing in different hosts
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