How ordinary saline emerged as a viable alternative to specialized viral transport media during the pandemic
The COVID-19 pandemic created unprecedented challenges for healthcare systems worldwide, with diagnostic testing emerging as a critical bottleneck in controlling the virus's spread. At the heart of this crisis was a seemingly mundane but crucial component: the viral transport medium (VTM). This specialized solution, designed to preserve virus specimens during transport to laboratories, became increasingly scarce as global testing demand skyrocketed.
Viral transport media is a sophisticated biochemical solution specifically formulated to preserve viral specimens during transportation from collection sites to testing laboratories.
Normal saline (0.9% sodium chloride solution) is a ubiquitous medical solution with several advantages:
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Up to 95% cost reduction potential
Previous research on other respiratory viruses had suggested that viral viability might not be essential for RT-PCR detection, as this method identifies genetic material rather than live virus. Studies had shown that dry swabs could detect influenza viruses even after two weeks at 37°C 1 .
Researchers collected nasopharyngeal samples from 35 known COVID-19 positive patients and 100 negative individuals using nylon flocked swabs 1 4 .
Each sample was divided and placed in both normal saline and commercial VTM (HiViral Transport Kit) 1 .
Samples were stored at both 4°C (refrigeration) and room temperature (25-32°C) to simulate various transport scenarios 1 .
Testing was performed at 48 hours, 120 hours (5 days), and 240 hours (10 days) to evaluate sample stability over time 1 .
All samples underwent RNA extraction using the QIAamp Viral RNA Mini Kit followed by RT-PCR using the TaqPath COVID-19 Combo Kit 1 .
| Aspect | Details |
|---|---|
| Participants | 35 COVID-19 positive, 100 negative individuals |
| Transport Media | Normal saline (0.9% NaCl) vs. Commercial VTM |
| Storage Conditions | 4°C (refrigeration) and room temperature (25-32°C) |
| Testing Time Points | 48 hours, 120 hours (5 days), 240 hours (10 days) |
| PCR Targets | Three SARS-CoV-2 genes: N, S, and Orf1ab |
Both saline and VTM detected 34 out of 35 positive samples, demonstrating equivalent sensitivity (97.1%). All 100 negative samples were correctly identified by both media (100% specificity) 1 .
The mean Ct values were remarkably similar between saline and VTM samples across all storage conditions and time points, with an overall mean difference of just 0.46 cycles 1 .
| Storage Condition | Time Point | Mean Ct (Saline) | Mean Ct (VTM) | Difference |
|---|---|---|---|---|
| 4°C | 48 hours | 27.76 | 28.46 | -0.70 |
| 4°C | 120 hours | 27.60 | 27.66 | -0.06 |
| 4°C | 240 hours | 27.75 | 28.29 | -0.54 |
| Room Temperature | 48 hours | 28.93 | 30.02 | -1.09 |
| Room Temperature | 120 hours | 27.58 | 27.53 | +0.05 |
Concurrent with the evaluation of saline as a transport medium, researchers explored innovative collection methods that could complement this approach. The saline gargle method emerged as a promising alternative to nasopharyngeal swabbing 2 8 .
In this approach, individuals gargle with sterile saline for several seconds and then expel the solution into a collection container. This method:
| Study | Sensitivity | Specificity | Stability | Patient Preference |
|---|---|---|---|---|
| PMC8092743 | 98% | N/R | 2 days at room temp | 89% preferred gargle |
| PLoS One 2023 | Comparable to VTM | Comparable to VTM | 7 days at various temps | N/R |
| Scientific Reports 2022 | 91.38% | 88.54% | 31 days with buffer | 97.1% preferred gargle |
| Item | Function | Examples/Alternatives |
|---|---|---|
| Normal Saline | Alternative viral transport medium; preserves viral RNA for detection | 0.9% sodium chloride solution |
| Commercial VTM | Standard transport medium for comparison; contains salts, nutrients, antibiotics | HiViral Transport Kit, Copan UTM |
| Nasopharyngeal Swabs | Sample collection from nasopharynx; nylon flocked design recommended | Nylon flocked swabs with plastic or wire shafts |
| RNA Extraction Kit | Isolation of viral RNA from samples for PCR detection | QIAamp Viral RNA Mini Kit (Qiagen) |
| RT-PCR Test Kit | Detection of SARS-CoV-2 RNA through amplification and fluorescence measurement | TaqPath COVID-19 Combo Kit (ThermoFisher) |
| Real-time PCR Instrument | Platform for performing RT-PCR and measuring results | ABI 7500 Real-Time PCR System (ThermoFisher) |
| Glycidol phosphate | C3H5O5P-2 | |
| Iodine monobromide | 7789-33-5 | BrI |
| Selenium disulfide | 7488-56-4 | SSe |
| thromboxane A2(1-) | C20H31O5- | |
| L-Ornithinoalanine | 25693-39-4 | C8H17N3O4 |
Found that phosphate-buffered saline (PBS) – another simple salt solution – could reliably preserve SARS-CoV-2 samples for up to 18 hours at room temperature 5 .
Tested normal saline, PBS, and locally produced VTM across various temperatures (-80°C to 37°C) for 7 days. All media showed comparable performance in maintaining viral RNA detection 7 .
Evaluated self-collected saline gargle samples from 19,620 individuals and found 90% sensitivity compared to nasopharyngeal swabs 3 .
These consistent findings across diverse geographical settings and laboratory configurations strengthened the case for saline as a viable VTM alternative.
The validation of saline as a transport medium has particularly significant implications for low-resource settings where:
With saline solution, these regions could implement robust testing programs using an affordable, accessible medium that maintains sample integrity even without refrigeration.
The COVID-19 pandemic highlighted critical vulnerabilities in global diagnostic infrastructure. The saline solution approach offers a flexible, scalable alternative that could be rapidly deployed during future outbreaks when specialized supplies might become scarce.
While current evidence is compelling, additional research could strengthen the case for saline:
The exploration of normal saline as a viral transport medium represents a compelling example of how pragmatic solutions often emerge from necessity during crises. This research demonstrates that sophisticated, expensive formulations are not always necessary for effective diagnostics and that sometimes the most effective solutions are already available in medical settings worldwide.