SARS-CoV-2 transmitters have more than three times higher viral loads than non-transmitters – practical use of viral load for disease control

SARS-CoV-2 Testing of Emergency Department Patients Using cobas® Liat® and eazyplex® Rapid Molecular Assays

Rapid testing for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) of patients presenting to emergency departments (EDs) facilitates the decision for isolation on admission to hospital wards. Differences in the sensitivity of molecular assays have implications for diagnostic workflows. This study evaluated the performance of the cobas^® Liat^® RT-PCR, which is routinely used as the initial test for ED patients in our hospitals, compared with the eazyplex^® RT-LAMP. A total of 378 oropharyngeal and nasal swabs with positive Liat^® results were analysed. Residual sample aliquots were tested using NeuMoDx™, cobas^® RT-PCR, and the eazyplex^® assay. Patients were divided into asymptomatic (n = 157) and symptomatic (n = 221) groups according to the WHO case definition. Overall, 14% of positive Liat^® results were not confirmed by RT-PCR. These samples were mainly attributed to 26.8% of asymptomatic patients, compared to 3.8% of the symptomatic group. Therefore, positive Liat^® results were used to provisionally isolate patients in the ED until RT-PCR results were available. The eazyplex^® assay identified 62% and 90.6% of RT-PCR-confirmed cases in asymptomatic and symptomatic patients, respectively. False-negative eazyplex^® results were associated with RT-PCR Ct values > 30, and were more frequent in the asymptomatic group than in the symptomatic group (38.1% vs. 5.1%, respectively). Both the Liat^® and eazyplex^® assays are suitable for testing symptomatic patients. Their use in screening asymptomatic patients depends on the need to exclude any infection or identify those at high risk of transmission.

A Prospective Study of Key Correlates for Household Transmission of Severe Acute Respiratory Syndrome Coronavirus 2

Background

Randomized controlled trials evaluated monoclonal antibodies for the treatment (Study 2067) and prevention (Study 2069) of coronavirus disease 2019 (COVID-19). Household contacts of the infected index case in Study 2067 were enrolled in Study 2069 and prospectively followed; these cohorts provided a unique opportunity to evaluate correlates of transmission, specifically viral load.

Methods

This post hoc analysis was designed to identify and evaluate correlates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission, adjusting for potential confounding factors related to source SARS-CoV-2 viral load and risk of SARS-CoV-2 acquisition in this population. Correlates of transmission were evaluated in potential transmission pairs (any infected household member plus susceptible household contact).

Results

In total, 943 participants were included. In multivariable regression, 2 potential correlates were determined to have a statistically significant (P < .05) association with transmission risk. A 10-fold increase in viral load was associated with a 40% increase in odds of transmission; sharing a bedroom with the index participant was associated with a 199% increase in odds of transmission.

Conclusions

In this prospective, post hoc analysis that controlled for confounders, the 2 key correlates for transmission of SARS-CoV-2 within a household are sharing a bedroom and increased viral load, consistent with increased exposure to the infected individual.

Differential expression of antiviral and immune-related genes in individuals with COVID-19 asymptomatic or with mild symptoms

COVID-19 is characterized by a wide range of symptoms where the genetic background plays a key role in SARS-CoV-2 infection. In this study, the relative expression of IRF9, CCL5, IFI6, TGFB1, IL1B, OAS1, and TFRC genes (related to immunity and antiviral activity) was analyzed in upper airway samples from 127 individuals (97 COVID-19 positive and 30 controls) by using a two-step RT-PCR. All genes excepting IL1B (p=0.878) showed a significantly higher expression (p<0.005) in COVID-19 cases than in the samples from the control group suggesting that in asymptomatic-mild cases antiviral and immune system cells recruitment gene expression is being promoted. Moreover, IFI6 (p=0.002) and OAS1 (p=0.044) were upregulated in cases with high viral loads, which could be related to protection against severe forms of this viral infection. In addition, a higher frequency (68.7%) of individuals infected with the Omicron variant presented higher viral load values of infection when compared to individuals infected with other variants (p<0.001). Furthermore, an increased expression of IRF9 (p<0.001), IFI6 (p<0.001), OAS1 (p=0.011), CCL5, (p=0.003) and TGFB1 (p<0.001) genes was observed in individuals infected with SARS-CoV-2 wildtype virus, which might be due to immune response evasion of the viral variants and/or vaccination. The obtained results indicate a protective role of IFI6, OAS1 and IRF9 in asymptomatic -mild cases of SARS-CoV-2 infection while the role of TGFB1 and CCL5 in the pathogenesis of the disease is still unclear. The importance of studying the dysregulation of immune genes in relation to the infective variant is stand out in this study.

Effects of Second Dose of SARS-CoV-2 Vaccination on Household Transmission, England

A single SARS-CoV-2 vaccine dose reduces onward transmission from case-patients. We assessed the potential effects of receiving 2 doses on household transmission for case-patients in England and their household contacts. We used stratified Cox regression models to calculate hazard ratios (HRs) for contacts becoming secondary case-patients, comparing contacts of 2-dose vaccinated and unvaccinated index case-patients. We controlled for age, sex, and vaccination status of case-patients and contacts, as well as region, household composition, and relative socioeconomic condition based on household location. During the Alpha-dominant period, HRs were 0.19 (0.13-0.28) for contacts of 2-dose BNT162b2-vaccinated case-patients and 0.54 (0.41-0.69) for contacts of 2-dose Ch4dOx1-vaccinated case-patients; during the Delta-dominant period, HRs were higher, 0.74 (0.72-0.76) for BNT162b2 and 1.06 (1.04-1.08) for Ch4dOx1. Reduction of onward transmission was lower for index case-patients who tested positive ≥2 months after the second dose of either vaccine.

Nasopharyngeal Wash with Normal Saline Decreases SARS-CoV-2 Viral Load: A Randomized Pilot Controlled Trial

Background

Although great progress has been made over the past 2 years in the scientific understanding of the biology, epidemiology, and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), case morbidity and fatality rates remain a great concern and continue to challenge the healthcare resources worldwide as novel variants emerge. There is therefore an urgent need for affordable and readily available strategies to reduce viral transmission. Previous studies in non-COVID-19 patients have demonstrated that administration of low-salt (isotonic but 0.0375% Na) and isotonic saline (0.9% Na) solutions has been associated with an immediate, significant reduction in the microbial antigens and a related decline of microbial burden. The aim of the present study was to determine the effect of nasal washes with normal saline 0.9% on nasopharyngeal viral load and outcome in hospitalized patients with COVID-19 pneumonia.

Methods

We performed a prospective, randomized, pilot, controlled trial in 50 patients with confirmed COVID-19 disease. Patients were randomized into two groups, the normal saline group (received normal saline 0.9% solution for nasopharyngeal wash) and the control group (no treatment). In the normal saline group, nasopharyngeal wash was performed every 4 hours for a 16-hour period. Twenty-four hours after the baseline nasopharyngeal swab (and 8 hours after the last wash in the normal saline group), a second nasopharyngeal swab was collected for the semiquantitative estimation of the SARS-CoV-2 viral load as determined by cycle threshold (Ct) values.

Results

In the normal saline group, mean N gene Ct values increased significantly 24 hours after the baseline measurement [ΔCt_day2−day1 = 1.87 ± 3.11 cycles, p = 0.007 (95% CI: 0.55 to 3.18)], indicating a decline in SARS-CoV-2 nasopharyngeal viral load by 8.9%. A significant decrease in mean N gene Ct values was observed in the control group, indicating an increase in viral load [ΔCt_day2-day1 = −2.12 ± 2.66, p < 0.001 (95% CI: −3.20 to −1.05)] by 9.7%. The difference between the two groups 24 hours after admission and nasopharyngeal wash was 3.09 cycles (p = 0.005, 95% CI: 0.97 to 5.20).

Conclusion

Nasal washes with normal saline effectively decreased the viral load during hospitalization and at follow-up.

Risk Factors for Slow Viral Decline in COVID-19 Patients during the 2022 Omicron Wave

Formulating termination of isolation (de-isolation) policies requires up-to-date knowledge about viral shedding dynamics. However, current de-isolation policies are largely based on viral load data obtained before the emergence of Omicron variant. In this retrospective cohort study involving adult patients hospitalised for COVID-19 between January and February 2022, we sought to determine SARS-CoV-2 viral shedding kinetics and to investigate the risk factors associated with slow viral decline during the 2022 Omicron wave. A total of 104 patients were included. The viral load was highest (Ct value was lowest) on days 1 post-symptom-onset (PSO) and gradually declined. Older age, hypertension, hyperlipidaemia and chronic kidney disease were associated with slow viral decline in the univariate analysis on both day 7 and day 10 PSO, while incomplete or no vaccination was associated with slow viral decline on day 7 PSO only. However, older age was the only risk factor that remained statistically significant in the multivariate analysis. In conclusion, older age is an independent risk factor associated with slow viral decline in this study conducted during the Omicron-dominant 2022 COVID-19 wave. Transmission-based precaution guidelines should take age into consideration when determining the timing of de-isolation.