Comparative evaluation of saliva and nasopharyngeal swab for SARS-CoV-2 detection using RT-qPCR among COVID-19 suspected patients at Jigjiga, Eastern Ethiopia

Comparison of SARS-CoV-2 RNA detection in different types of clinical specimens among suspected COVID-19 patients in Addis Ababa, Ethiopia

Although nasopharyngeal swabs (NPSs) are superior to saliva specimens, saliva can be used as an alternative specimen for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing. Moreover, studies have reported contradicting findings on whether SARS-CoV-2 can be detected in urine or not. Thus, we aimed to evaluate the diagnostic utility of NPSs, saliva and urine specimens in suspected COVID-19 patients. We conducted a cross-sectional study among a total of 604 specimens collected from 219 individuals suspected for COVID-19 from February to July 2022. We recruited participants from two COVID-19 isolation and treatment centers in Addis Ababa. We analyzed the specimens by real-time reverse transcriptase polymerase chain reaction (RT-PCR) with a Cobas 8800 automated system. The presence of SARS-CoV-2 in NPS, saliva, and urine samples was measured by cycle threshold (Ct) values. Descriptive statistics such as frequency, percent, and mean with standard deviation were used to summarize participants characteristics. We conducted chi-square test to compare RT‒PCR results of NPS, saliva and urine specimens. All data was analyzed by SPSS version 27, and the level of significance was set at a p value ≤ 0.05. Of the 219 participants, 126 (57.5%) were positive for SARS-CoV-2 either from NPS, saliva, urine or all specimens. The rate of SARS-CoV-2 detection was significantly higher in NPS (53.9%) than in saliva (35.2%; p = 0.001) and urine (9.0%; p = 0.001) specimens. The percentage of positive agreement between NPS and saliva was 92.2%, while negative agreement was 66.9%. The overall agreement between NPS and saliva was 75.8% (K = 0.53, p < 0.001). In addition, there was a significant correlation in Ct values of both ORF1ab and E genes between the paired NPS and saliva specimens. There was significant positive correlation between NPS and saliva specimens Ct values of both ORF1ab and E genes and days from onset of symptoms to specimen collection. SARS-CoV-2 was significantly detected in NPS than in saliva and urine specimens. Although NPS is better for SARS-CoV-2 detection, saliva specimen can be used as an alternative clinical specimen in resource-limited settings where access to swabs is limited. Both saliva and urine could be sources of viral transmission.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-024-00892-9.

Evaluating diagnostic accuracy of an RT-PCR test for the detection of SARS-CoV-2 in saliva

BACKGROUND AND OBJECTIVE

Saliva has been proposed as a potential more convenient, cost-effective, and easier sample for diagnosing SARS-CoV-2 infections, but there is limited knowledge of the impact of saliva volumes and stages of infection on its sensitivity and specificity.

METHODS

In this study, we assessed the performance of SARS-CoV-2 testing in 171 saliva samples from 52 mostly mildly symptomatic patients (aged 18 to 70 years) with a positive reference standard result at screening. The samples were collected at different volumes (50, 100, 300, and 500 µl of saliva) and at different stages of the disease (at enrollment, day 7, 14, and 28 post SARS-CoV-2 diagnosis). Imperfect nasopharyngeal (NP) swab nucleic acid amplification testing was used as a reference. We used a logistic regression with generalized estimating equations to estimate sensitivity, specificity, PPV, and NPV, accounting for the correlation between repeated observations.

RESULTS

The sensitivity and specificity values were consistent across saliva volumes. The sensitivity of saliva samples ranged from 70.2% (95% CI, 49.3-85.0%) for 100 μl to 81.0% (95% CI, 51.9-94.4%) for 300 μl of saliva collected. The specificity values ranged between 75.8% (95% CI, 55.0-88.9%) for 50 μl and 78.8% (95% CI, 63.2-88.9%) for 100 μl saliva compared to NP swab samples. The overall percentage of positive results in NP swabs and saliva specimens remained comparable throughout the study visits. We observed no significant difference in cycle number values between saliva and NP swab specimens, irrespective of saliva volume tested.

CONCLUSIONS

The saliva collection offers a promising approach for population-based testing.

Self-Diagnosis of SARS-CoV-2 from Saliva Samples at Home: Isothermal Amplification Enabled by Do-It-Yourself Portable Incubators and Laminated Poly-ethyl Sulfonate Membranes

COVID-19 made explicit the need for rethinking the way in which we conduct testing for epidemic emergencies. During the COVID-19 pandemic, the dependence on centralized lab facilities and resource-intensive methodologies (e.g., RT-qPCR methods) greatly limited the deployment of widespread testing efforts in many developed and underdeveloped countries. Here, we illustrate the development of a simple and portable diagnostic kit that enables self-diagnosis of COVID-19 at home from saliva samples. We describe the development of a do-it-yourself (DIY) incubator for Eppendorf tubes that can be used to conduct SARS-CoV-2 detection with competitive sensitivity and selectivity from saliva at home. In a proof-of-concept experiment, we assembled Eppendorf-tube incubators at our home shop, prepared a single-tube mix of reagents and LAMP primers in our lab, and deployed these COVID-19 detection kits using urban delivery systems (i.e., Rappifavor or Uber) to more than 15 different locations in Monterrey, México. This straightforward strategy enabled rapid and cost-effective at-home molecular diagnostics of SARS-CoV-2 from real saliva samples with a high sensitivity (100%) and high selectivity (87%).