Inhale, then exhale: start afresh to diagnose Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by non-invasive face-mask sampling technique.

To the Editor,

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is leading to an exponential growth of cases and the total number of confirmed cases has exceeded 3 million. Although respiratory droplets are the major route of transmission of the virus, van Doremalen et al. in a recent study revealed that aerosol and fomites can be plausible routes of transmission [1].

Nasopharyngeal (NP) swabs are the recommended sample and RT-PCR is the cardinal modality for SARS-CoV-2 detection. The method of NP swab collection is invasive and mandates the availability of trained staff and personal protective equipment. Also, NP swab specimen collection carries a theoretical risk of transmitting the virus. The concern of false-negative results due to faulty technique necessitates an alternative method of sample collection.

Hence, the current need is for simple, non-invasive methods of sampling. Few studies have proposed the isolation of virus from self-collected specimens, like tears, saliva, urine and stools. Another alternative method is sampling from the mask of the patient. The size of the respiratory droplet is from >5 to 10 μm in diameter and Edwards et al. demonstrated that during normal breathing many people generate a substantial number of aerosols ~150 nm in diameter [2]. Hence, N95 masks, which are widely recommended for prophylaxis against inhaled viral droplets and aerosols, can be sampled and can offer an easy adjunct for NP samples. This method will be a solution for the institutions that are suffering because of rising demand for Viral Transport Medium and swab sticks, and the requirement of trained medical personnel and personal protective equipment will also decrease.

The N95 masks use charged electret fibres as the filtering medium, and in vitro experiments have demonstrated that they collect >95% of the aerosolized virus [3]. Attempts have been made previously to collect virus aerosols by different methods, including impaction, impingers and gelatin or nucleopore air filters attached to air pumps. In 2008, Huynh et al., developed a novel prototype mask-like sampling device. It was made from impermeable and stretchable PVC [4]. It contained an electret (25-mm diameter) opposite the nose and mouth region. This sampling device had low airflow resistance (15 mmH2O) at normal respiratory flows and was able to collect 80% of 0.52-µm latex particles (virus droplet representative). Hence, after sampling, electret can be easily removed, placed in RNA lysis buffer and PCR can be performed [4]. In a recent study from the University of Leicester by Williams et al., face-mask sampling offered an efficient and non-invasive method for detection of exhaled Mycobacterium tuberculosis, with a high sensitivity of 86·5% [5]. This group is also working on the isolation of SARS-CoV-2 from the mask. In this simple technique, the person wears a face mask containing strips made of a gelatin sampling matrix for a duration of 30 minutes. These moist strips will trap the virus in the matrix [5] and can then be preserved after drying out and used for virus isolation. The preserved strips can be directly transported to the laboratory, precluding the need for special storage before analysis. This method obviates the need for health-care workers, and no expertise is required to collect the samples (Fig. 1 a,b).

Fig. 1

COVID-19 diagnostic test by face-mask sampling.

However, although these innovative approaches are promising tools, their efficiency needs to be confirmed by further studies. Standardization of the duration for which the patient needs to wear the mask is required as the proportion of virus droplets produced per hour in asymptomatic carriers or patients with a smaller viral load is not similar. It will also be relevant to think whether or not the sampling from the mask will provide us with a true representation of the ongoing pathogenies in the respiratory tract. The major limitation of this method is that it is patient-dependent. Non-compliance in a claustrophobic patient can limit the sensitivity of detection. Another concern is the storage of samples. An NP swab in Viral Transport Medium can be refrigerated at 2°C–8°C for 48 hours and at –70°C for a longer duration and has a shelf life of 5 years. Storage and shelf life of the mask with gelatin strips warrants more studies.

Since the outbreak of SARS-CoV-2, researchers have been trying to develop an alternative method of sample collection. This approach will be advantageous, simple, safe, easy to use and non-invasive. A larger population can be sampled in less time and the method can be used for a wide range of age groups, especially children and asymptomatic and non-cooperative patients. Transportation of the masks would be easier than that of NP swabs as there is no risk of sample contamination or leakage. The cost of both the mask and Viral Transport Medium with swab are comparable ($2.50). The method of collection will be easier and less bio-hazardous waste will be generated. Also, other respiratory viruses can be detected from one sample using multiplex PCR, providing diagnosis for infections other than SARS-CoV-2. The sensitivity and specificity can be derived from further studies, which can compare the face-mask sampling to nasopharyngeal PCR. Even though studies are in the preliminary stages, this innovative approach is a breath of fresh air and provides a new insight for the future.

Transparency declaration

The authors have stated that there are no conflicts of interest.

Funding

None.

Authors' contributions

RK and AA were responsible for writing the original draft and for conceptualization. MB and PR responsible for reviewing and editing the article.