Stability of SARS-CoV-2 RNA in Nonsupplemented Saliva

Abstract

The expense of saliva collection devices designed to stabilize severe acute respiratory syndrome coronavirus 2 RNA is prohibitive to mass testing. However, virus RNA in nonsupplemented saliva is stable for extended periods and at elevated temperatures. Simple plastic tubes for saliva collection will make large-scale testing and continued surveillance easier.

Keywords: 2019 novel coronavirus disease; COVID-19; SARS-CoV-2; coronavirus disease; diagnostics; respiratory infections; saliva; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Stability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA (N1) detection in saliva. A) Detection of SARS-CoV-2 RNA in 20 saliva samples on day of sample collection (fresh) did not significantly change after storage at −80°C (to assess the effect of a freeze/thaw cycle), 3 days at 30°C, or 5 days at RT (recorded as ≈19°C). Detection of N1 remained similar to that of freshly collected samples, regardless of starting C_t value (Pearson r = −0.085, p = 0.518). B) At RT, detection remained stable for up to 25 days. Colored dashed lines track the same sample through different storage conditions. Black horizontal dashed lines represent C_t 38, which we applied as the cutoff to determine sample positivity. Samples that remained not detected after 45 cycles are depicted on the x-axis. C_t, cycle threshold; RT, room temperature.

Figure 2

Detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in saliva samples tested for infectious SARS-CoV-2. SARS-CoV-2 N1 detection (C_t values) measured by quantitative reverse transcription PCR for each saliva sample incubated with Vero-E6 cells for 72 hours. The orange diamond depicts the only sample that produced plaque-forming units (titer increase of 3.79 × 10⁴ PFU/mL; purple circles indicate samples that did not produce plaque-forming units by 72 h after inoculation; dashed lines indicate C_t 38 (the cutoff for sample positivity); gray shading indicates C_ts below the limit of detection. C_t, cycle threshold.