To fight the COVID-19 pandemic, you need rapid and accurate tests for the virus. Nasopharyngeal and oropharyngeal swabs are used to detect COVID-19. However, taking a nasopharyngeal swab requires close contact between healthcare workers and patients and can cause throat irritation, sneezing, and coughing. It poses a risk of healthcare workers being exposed to the virus. In addition, epithelial sampling from the nasopharynx and oropharynx causes discomfort and, in patients with thrombocytopenia, may cause bleeding. These limitations make smears inconvenient for serial viral load monitoring. The saliva test is a non-invasive test suitable for rapid mass diagnosis of coronavirus.

Content

Saliva Test: Is It Necessary to Cough Up Saliva from The Throat

Posterior oropharyngeal saliva

In 2020, Chinese scientists were the first to detect SARS-CoV-2 in saliva. They used PCR to examine saliva samples from 23 COVID-19 patients of varying severity. Coronavirus RNA was found in saliva in 87% of patients.

In this study, posterior oropharyngeal saliva was used. Patients coughed up a pharyngeal secret to pass a saliva test for coronavirus.

Posterior oropharyngeal saliva is a secret formed during coughing or coughing and refers to respiratory secretions – it mixes the secretions of the upper (nasopharynx) and lower (bronchi, lungs) respiratory tract. In contrast, oral saliva is produced by the salivary glands and does not belong to the group of respiratory samples.

Oral saliva

Research on rhesus macaques has shown that SARS-CoV infects epithelial cells in the salivary gland ducts. A study of saliva samples from patients with COVID-19 found that the saliva contains live viruses. Respiratory viruses are transmitted by contact and drip routes. Drops of saliva are released when coughing. A study of seasonal flu has shown that the virus is contained in ordinary exhaled air in the form of a fine aerosol. These facts confirm that COVID-19 can be transmitted through saliva, even if the patient does not have respiratory symptoms.

The epithelium of the respiratory tract is covered with cilia. The cilia of the respiratory tract oscillate in one direction and help the outflow of mucus. Therefore, saliva also contains the secrets of the lungs and nasopharynx.

Italian scientists were the first to detect SARS-CoV-2 in oral saliva. Saliva was collected by salivation, avoiding coughing or expectoration.

This study made an important discovery: some patients with COVID-19 may have a negative nasopharyngeal PCR test but a positive saliva test. Thus, two consecutive negative nasopharyngeal tests do not always mean that the patient is not contagious.

Conclusion

Combining saliva and respiratory samples could increase the sensitivity of the coronavirus test and reduce false negatives.

Image source: https://journals.sagepub.com/doi/10.1177/0022034520969670

Saliva analysis for COVID-19 – a safe and fast way to test

The patient is asked to cough saliva from the throat into a sterile test tube for study. Medical personnel is not needed to take the sample. It reduces the risk of medical personnel becoming infected with the coronavirus. Saliva samples can be collected outside hospitals, reducing the likelihood of airborne infections.

A saliva sample does not require invasive procedures, so it is faster and more comfortable for the patient and is suitable for mass testing on COVID-19. Since patients collect saliva independently, there is no need to wait for a medical professional to take samples. It means that the result of the coronavirus test will be obtained faster. It significantly reduces the time until the test result is obtained.

To detect SARS-CoV-2 infection faster, the scientists proposed pooling 5-10 saliva samples into one pool. Each pool undergoes PCR, and further testing of individual samples is carried out only in pools that have tested positive for coronavirus. This strategy is suitable for areas with a low prevalence of SARS-CoV-2.

A Chance to Replace A Nasopharyngeal Swab with A Saliva Test for Coronavirus

COVID-19 saliva test accuracy in adults

To compare the reliability of detecting SARS-CoV-2 in PCR testing with a nasopharyngeal swab and saliva-based testing, Canadian scientists conducted a systematic review and meta-analysis of 16 studies. The meta-analysis included the results of PCR tests of 5922 patients based on saliva samples, nasopharyngeal swabs, or both.

The diagnostic sensitivity of a saliva test and a nasopharyngeal swab for coronavirus is comparable. The sensitivity of saliva PCR was 83.2%, and the specificity was 99.2%. The sensitivity of the nasopharyngeal swab was 84.8%, and the specificity was 98.9%.

The study was published in The Journal of the American Medical Association.

Comparison of the accuracy of the covid-19 saliva test in children and adults

Mexican scientists investigated the sensitivity and specificity of the saliva PCR test for SARS-CoV-2 in children and adults. The sensitivity of the saliva test in children was below the expected value.

The study included 156 children, of whom 128 had at least one comorbid condition, and 91 showed clinical symptoms of COVID-19. Adult group – 326 hospital staff, of which 271 had symptoms of COVID-19.

The scientists compared the results of nasopharyngeal and oropharyngeal swabs with those of saliva samples. Immediately after the swabbing procedure, participants were asked to spit 5 times into a sterile 50 ml tube gently. Participants were not asked to cough up or enrich their samples with sputum.

In the group of children, the sensitivity of the saliva-based diagnostic test was 82.3%, and the specificity was 95.6%. Of the 23 participants who tested positive for SARS-CoV-2 in at least one type of specimen, the virus was detected in saliva but not in a nasopharyngeal or oropharyngeal swab, while 3 participants had a nasopharyngeal or oropharyngeal swab. The oropharynx was positive, and saliva was negative. The viral load of a nasopharyngeal or oropharyngeal swab and saliva did not differ significantly.

In the adult group, the sensitivity of the saliva-based test was 77.8%.

In contrast to children and adolescents, saliva showed a significantly lower viral load than nasopharyngeal or oropharyngeal swabs in adults. It may be due to the different dynamics of virus isolation in the oral cavity. These dynamics depend on age, concomitant diseases, and medication.

The study was published in the journal Frontiers in Pediatrics.

Conclusion

The sensitivity of a saliva test for coronavirus is not high enough to replace a nasopharyngeal or oropharyngeal swab. Neither swab nor saliva can detect all those infected with SARS-CoV-2.

However, given the ease of obtaining samples, saliva tests can be used in mass screening programs for COVID-19.

Also, a saliva test for COVID-19 will help correct false-negative results of a nasopharyngeal swab. A recent study identified asymptomatic carriers among healthcare workers with a negative salivary-only nasopharyngeal swab PCR result. A nasopharynx swab can give a false-negative result for coronavirus in about 30% of cases after the onset of symptoms. Therefore, for a more accurate diagnosis of COVID-19, it will be helpful to compare the results of samples from the nasopharynx and saliva.

Rapid Saliva Test for Coronavirus Antigens

Rapid coronavirus tests can be used outside of medical offices or laboratories. These tests are used when a swift population diagnosis is needed: in theaters, schools, universities, gyms, restaurants, shopping centers, and airports. Rapid tests do not require medical personnel or special equipment.

A rapid antigen test detects the presence of a viral protein in a sample which makes it different from other medical tests that detect antibodies or nucleic acids. The antigen test does not see the presence of antibodies to SARS-CoV-2. It simply determines the presence of the virus directly at the time of analysis. Therefore, the rapid test is suitable for a mass screening program for COVID-19.

The SARS-CoV-2 rapid saliva test provides results in less than 10 minutes by detecting the presence of a spike protein in a saliva sample.

How to find out the result of a rapid saliva test for COVID-19

There are two marks on the test: test (T) and control (C). If 2 colored bands are visible (both test and control lines), the subject is infected. Moreover, if only the control line is visible, the subject is not infected. The test is considered invalid if the C-line is not visible, regardless of the presence of the T-line.

Image source: https://journals.sagepub.com/doi/10.1177/0022034520969670

There is conflicting information about the sensitivity of the rapid saliva test. Some studies report high sensitivity (93%), others report low.

Conclusion

Saliva diagnostics of SARS-CoV-2 are adequate for testing in crowded places. An important task is to identify asymptomatic carriers of coronavirus before they enter the premises and spread the infection. Rapid antigen tests in saliva could be a pivotal strategy to contain the pandemic.

Virus Detection Technique Based on DNA Nanoswitches

Swab PCR-analyse complexities

To transport the smear to COVID-19, you need expensive reagents that stabilize the virus.

The laboratory uses a polymerase chain reaction (PCR) machine. PCR uses enzymes to increase the number of copies (amplifies) of viral DNA fragments to detect the virus. Enzymes increase the cost and complexity of analysis due to the requirements for their storage, transportation, and use temperatures.

Diagnosis of viral RNA is complicated by limited detection time, laboratory resources, low or changing viral load, cross-reactive IgM antibodies (antibodies to one virus react to antibodies to another).

DNA nano-switches instead of PCR

Scientists from the New York State University at Albany have developed a way to detect viral RNA without amplification.

Soft-switches are used to analyze DNA. The switches are configured to detect a specific viral RNA. The original shape of the switches is linear. In the presence of viral RNA during gel electrophoresis, the switches change shape to a loop. To amplify the signal of the DNA switches, the viral RNA is fragmented, and the switches are assigned a more significant number of targets.

The DNA-based nanoswitch analysis does not require pre-amplification using enzymes but is compatible. At the same time, pre-amplification gives a sharp improvement in the signal of nanoswitches.

DNA nanoswitches are sensitive. They can detect DNA oligonucleotides and microRNAs (~22 nucleotides long).

The analysis can be performed simultaneously for 5 viral targets. Loops of different sizes must be programmed for additional targets to perform the analysis. Also, the study can distinguish different strains of the same virus even with high genetic similarity.

Since DNA switches can be programmed, the system is universal. It is suitable for detecting various viruses, including Zika (ZIKV), dengue (DENV), and SARS-CoV-2 viruses. The system detects SARS-CoV-2 in 2 hours: 1 hour for amplification, 40 minutes for incubation with nanoswitches, 25 minutes for gel electrophoresis.

The DNA switch system has been tested to detect viral RNA in biological fluids, including urine and saliva.

The study was published in the Science journal.

Conclusions

Saliva collection does not require specialized medical personnel. Since the test subjects collect saliva samples themselves, the risk of infecting healthcare workers is drastically reduced. Given the ease of obtaining samples, saliva tests can be used in mass screening programs for COVID-19.

The sensitivity of the saliva test is not high enough to replace a nasopharyngeal or oropharyngeal swab. However, saliva testing for coronavirus will help correct false-negative smear results and contain the pandemic.

Useful article, necessary information? Share it!

Someone will also find it useful and necessary:

References

Our Telegram channel:

Related posts: