Asymptomatic Workers Research Articles

Potential SARS-CoV-2 infectiousness among asymptomatic healthcare workers.

A majority of SARS-CoV-2 infections are transmitted from a minority of infected subjects, some of which may be symptomatic or pre-symptomatic. We aimed to quantify potential infectiousness among asymptomatic healthcare workers (HCWs) in relation to prior or later symptomatic disease. We previously (at the onset of the SARS-CoV-2 epidemic) performed a cohort study of SARS-CoV-2 infections among 27,000 healthcare workers (HCWs) at work in the capital region of Sweden. We performed both SARS-CoV-2 RT-PCR and serology. Furthermore, the cohort was comprehensively followed for sick leave, both before and after sampling. In the present report, we used the cohort database to quantify potential infectiousness among HCWs at work. Those who had sick leave either before or after sampling were classified as post-symptomatic or pre-symptomatic, whereas the virus-positive subjects with no sick leave were considered asymptomatic. About 0.2% (19/9449) of HCW at work were potentially infectious and pre-symptomatic (later had disease) and 0.17% (16/9449) were potentially infectious and asymptomatic (never had sick leave either before nor after sampling). Thus, 33% and 28% of all the 57 potentially infectious subjects were pre-symptomatic or asymptomatic, respectively. When a questionnaire was administered to HCWs with past infection, only 10,5% of HCWs had had no indication at all of having had SARS-CoV-2 infection ("truly asymptomatic"). Our findings provide a unique quantification of the different groups of asymptomatic, potentially infectious HCWs.

400. Impact of SARS-CoV-2 Test-based Strategy to Reduce Quarantine Days Among Asymptomatic Healthcare Workers After Household Exposure

BackgroundAppropriate staffing is essential to provide safe patient care. During the COVID-19 pandemic, healthcare workers (HCWs) are missing work days due to illness or high-risk exposure (HRE) to an infected person. To avoid staffing shortages, we implemented a SARS-CoV-2 test-based strategy among asymptomatic HCWs after HRE to facilitate early return to work.MethodsIn July 2020, our institution implemented a SARS-CoV-2 RT-PCR test-based strategy among HCWs within 7 days of HRE. HCWs were defined as any paid or unpaid persons directly or indirectly involved in patient care. HRE was defined as close contact < 6 feet with an infected household member without use of mask and lasting for ≥ 15 minutes. Contact with a patient or coworker was not considered high-risk due to universal masking and eye protection use. HCWs underwent SARS-CoV-2 RT PCR testing of a nasopharyngeal swab at least once (1-2 days post-exposure) or twice (5-7 days post-exposure). HCWs with symptoms at baseline were excluded. HCWs who were asymptomatic during evaluation were considered as truly asymptomatic (TA). Saved work-days (SWD) were calculated based on number of days saved due to testing strategy compared to the Centers for Disease Control and Prevention’s recommended 14-day quarantine. HCWs were allowed to return to work within 7 days of HRE if they tested negative, or after completing 10-day isolation period ± improvement in symptoms from symptom onset if they tested positive.ResultsBetween 07/01/2020 to 12/31/2020, 450 unique asymptomatic HCWs underwent SARS-CoV-2 testing. Of those, 84% were women and median age was 36 years, 347 tested negative and 103 tested positive. Of those positives, 33% of HCWs tested positive on day 2 after HRE with 141 SWDs (average 2 days/person). Only 37% were TA positives. Of those negatives, 94% were TA SARS-CoV-2 negative with 2620 SWDs (average 7.5 days/person). There were no healthcare outbreaks related to HCWs allowed to return to work following this strategy. Asymptomatic healthcare workers commonly tested positive for SARS-CoV-2 on day 2 from household exposure compared to other daysConclusionTest-based strategy among asymptomatic HCWs with HRE reduced loss of workdays and helped limit staffing shortages. Majority of positive HCWs developed symptoms after positive SARS-CoV-2 testing, which may support allowing most fully vaccinated HCWs with no COVID-like symptoms to continue to work unless symptomatic.Disclosures All Authors: No reported disclosures

Carriage of Staphylococcus aureus among food handlers: An ongoing challenge in public health

Staphylococcus aureus is a commensal bacterium known to colonize the skin, nares, and gastrointestinal tract of humans. Asymptomatic workers can contaminate food via manual contact or through respiratory secretions thus becoming the source of staphylococcal food poisoning. This gastrointestinal intoxication occurs after the ingestion of food contaminated by enterotoxin-producing Staphylococcus aureus. Although most individuals overcome the infection without medical assistance and make a full recovery, in rare cases the infection can be life-threatening. Hence, Staphylococcus aureus food contamination represents a serious problem for both the food industry and healthcare systems. In the last few decades, many studies have investigated the prevalence of carriers among food handlers. We present an overview of all investigations carried out on nasal carriers working in different food industry settings highlighting the risk associated with cross-contamination.

Regular testing of asymptomatic healthcare workers identifies cost-efficient SARS-CoV-2 preventive measures.

Protecting healthcare professionals is crucial in maintaining a functioning healthcare system. The risk of infection and optimal preventive strategies for healthcare workers during the COVID-19 pandemic remain poorly understood. Here we report the results of a cohort study that included pre- and asymptomatic healthcare workers. A weekly testing regime has been performed in this cohort since the beginning of the COVID-19 pandemic to identify infected healthcare workers. Based on these observations we have developed a mathematical model of SARS-CoV-2 transmission that integrates the sources of infection from inside and outside the hospital. The data were used to study how regular testing and a desynchronisation protocol are effective in preventing transmission of COVID-19 infection at work, and compared both strategies in terms of workforce availability and cost-effectiveness. We showed that case incidence among healthcare workers is higher than would be explained solely by community infection. Furthermore, while testing and desynchronisation protocols are both effective in preventing nosocomial transmission, regular testing maintains work productivity with implementation costs.

SARS-CoV-2 seroprevalence among healthcare workers from a tertiary care center in Riyadh, Saudi Arabia.

Objectives:To calculate the seroprevalence of asymptomatic healthcare workers (HCWs) in our institution.Methods:We conducted a cross-sectional study among asymptomatic HCWs in a large hospital during the peak of the pandemic (from July to August 2020 and followed them up until February 2021) in Riyadh, Saudi Arabia. We collected the data in a Microsoft Word document after collecting a single serum sample for detection of antibodies from each participant then we compared the results statically in Microsoft Excel tables.Results:We enrolled 188 participants and measured their IgG antibodies from venous blood samples using CLIA. Six (3.2%) had positive antibodies despite being asymptomatic. Most of these were from non-COVID-19 working areas (4 out of 6), but all had an exposure with a positive COVID-19 patient at some point in the preceding 2 months.Conclusions:Our results are consistent with similar local studies showing low seroprevalence among HCWs while most positive cases are from non-COVID-19 areas. Despite this low seroprevalence, HCWs are still considered a high-risk group; hence, there is a need to encourage strict implementation and adherence to infection control measures and vaccination among HCWs, especially when these measures are relaxed on the national level.

What We Need to Do to Improve Our Immune System Despite the Use of Vaccination for COVID-19?

In our daily practice, we have heard more and more frequent reports of people infected with SARS-CoV-2, even having received one or two doses of vaccine for COVID-19. In the article written by Angel et al. (2021) entitled Association Between Vaccination with BNT162b2 and Incidence of Symptomatic and Asymptomatic SARS-CoV-2 Infections Among Health Care Workers, the authors concluded that the effectiveness of the vaccine in symptomatic SARS-CoV-2 infection reduced the incidence of this infection if you compared with unvaccinated health care worker. But the incidence was not reduced in the asymptomatic health care workers, where they found that vaccinated people were more likely to have SARS-CoV-2 if compared to unvaccinated people.

A cross-sectional study of SARS-CoV-2 seroprevalence among asymptomatic healthcare workers in a tertiary healthcare centre: Assessing the impact of PPE guidelines

PurposeThe present study estimates the seroprevalence of SARS-COV-2 among asymptomatic HCWs and assess the impact of various categories of PPE. MethodsA cross-sectional study of asymptomatic HCW using different levels of PPE as per their risk profile was undertaken between 18th and 24th September 2020. Participant demographics and other relevant details including the levels of PPE used were recorded using a customized questionnaire. IgG antibodies against SARS-COV-2 were detected by chemiluminescence method & used as a surrogate marker for incomplete protection. ResultsOut of 1033 HCWs tested, overall SARS-COV-2 sero-prevalence was 25.8%. Univariate and multivariate analysis both demonstrated that ancillary workers including security staff (OR 5.589, P ​< ​0.001) and sanitary workers (OR 3.946, P ​< ​0.001) were at significantly higher risk of seropositivity irrespective of the PPE used as per guidelines, whereas doctors were at significantly lower risk of seropositivity (OR 0.307, P ​= ​0.005). Staff working in office areas was associated with reduced risk of seropositivity (OR 0.21, P ​= ​0.045). ConclusionsWe document high seroprevalence of SARS-COV-2 antibodies in asymptomatic HCWs. Doctors who are at the highest risk had the lowest seropositivity and seroprevalence among office staff having a risk level comparable to the general community was lower than that reported in general population, supporting the efficacy of PPE practices as per guidelines in these groups. In contrast, much higher rates of seropositivity were seen among ancillary workers despite the availability of adequate PPE. Active screening, proper PPE use as per guidelines, and regular infection control trainings including Covid appropriate behaviour are therefore essential to contain COVID-19 spread among HCW & preventing them to transfer infection to the patients.

Same Virus, Different Course: The Relationship Between Monocyte Chemoattractant Protein-1 and Surfactant Protein-A Levels And Clinical Course and Prognosis of COVID-19

Introduction: To date, over 165 million people have been infected in the COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 which emerged in Wuhan, China in December 2019. This study examined the relation between serum monocyte chemoattractant protein-1 and surfactant protein-A levels and the clinical course and prognosis of COVID-19. Materials and Methods: The study included a total of 108 subjects. Those in the patient group (n= 88) were diagnosed with COVID-19 using real-time PCR analysis of nasopharyngeal swab samples and treated in the Pulmonary Diseases Intensive Care Unit and the Infectious Diseases Department between March 24 and May 20. The control group (n= 20) included asymptomatic healthcare workers whose real-time PCR results during routine COVID-19 screening in our hospital were negative. Results: The COVID-19 patient group had significantly higher monocyte chemoattractant protein-1 and SP-A levels compared to the control group (p= 0.001, p= 0.001). Patients who developed macrophage activation syndrome had significantly higher monocyte chemoattractant protein-1 and surfactant protein-A levels than those who did not both at admission (p= 0.001, p= 0.001) and on day 5 of treatment (p= 0.05, p= 0.04). Similarly, monocyte chemoattractant protein-1 and surfactant protein-A levels were significantly higher in patients who developed acute respiratory distress syndrome compared to those who did not at both time points (p= 0.001 for all). Both parameters were significantly higher in non-surviving COVID-19 patients compared to survivors (p= 0.001 for both). Conclusion: Monocyte chemoattractant protein-1 and surfactant protein-A are on opposing sides of the inflammatory balance, and SP-A may be a pneumoprotein of importance in the presentation, course, prognosis, and possibly the treatment of COVID-19 in the future.

Evaluation of the Advanta Dx SARS-CoV-2 RT-PCR Assay, a High-Throughput Extraction-Free Diagnostic Test for the Detection of SARS-CoV-2 in Saliva: A Diagnostic Accuracy Study.

Nasopharyngeal swab specimen (NPS) molecular testing is considered the gold standard for SARS-CoV-2 detection. However, saliva is an attractive, noninvasive specimen alternative. The aim of the study was to evaluate the diagnostic accuracy of Advanta Dx SARS-CoV-2 RT-PCR saliva-based assay against paired NPS tested with either NeumoDxTM SARS-CoV-2 assay or Abbott Real Time SARS-CoV-2 assay as the reference method. We prospectively evaluated the method in two settings: a diagnostic outpatient and a healthcare worker screening convenience sample, collected in November–December 2020. SARS-CoV-2 was detected in 27.7% (61/220) of diagnostic samples and in 5% (10/200) of screening samples. Overall, saliva test in diagnostic samples had a sensitivity of 88.5% (77.8–95.3%) and specificity of 98.1% (94.6–99.6%); in screening samples, the sensitivity was 90% (55.5–99.7%) and specificity 100% (98.1–100%). Our data suggests that the Fluidigm Advanta Dx RT-PCR saliva-based assay may be a reliable diagnostic tool for COVID-19 diagnosis in symptomatic individuals and screening asymptomatic healthcare workers.

Factors Affecting Adverse Health Effects of Gasoline Station Workers.

This cross-sectional study examined the risk factors affecting adverse health effects from benzene exposure among gasoline station workers in Khon Kean province, Thailand. An interview questionnaire of adverse symptoms relating to benzene toxicity was administered to 151 workers. Area samplings for benzene concentration and spot urine for tt-muconic acid (tt-MA), a biomarker of benzene exposure, were collected. The factors associated with adverse symptoms were analysed by using multiple logistic regression. It was found that these symptoms mostly affected fuelling workers (77.5%), and the detected air benzene reached an action level or higher than 50% of NIOSH REL (>50 ppb). The top five adverse symptoms, i.e., fatigue, headache, dizziness, nasal congestion, and runny nose, were reported among workers exposed to benzene. More specific symptoms of benzene toxicity were chest pain, bleeding/epistaxis, and anaemia. The detected tt-MA of workers was 506.7 ug/g Cr (IQR), which was a value above the BEI and higher than that of asymptomatic workers. Risk factors significantly associated with adverse symptoms, included having no safety training experience (ORadj = 5.22; 95% CI: 2.16–12.58) and eating during work hours (ORadj = 16.08; 95% CI: 1.96–131.74). This study urges the tightening of health and safety standards at gasoline stations to include training and eating restrictions while working in hazardous areas.

SARS-CoV-2 positivity rates in asymptomatic workers at a cancer referral center in Mexico City: A prospective observational study in the context of adapting hospitals back to regular practice

BackgroundHealthcare workers are at increased risk of SARS-CoV-2 infection. The positivity rates in hospitals that do not receive patients with COVID-19, such as the National Cancer Institute (INCan) in Mexico, and the associated factors are unknown. ObjectiveTo assess the incidence and factors associated with SARS-CoV-2 infection in health workers at INCan. MethodsA cohort study of 531 workers who were followed for 6 months. RT-PCR analysis of saliva and nasopharyngeal swab samples were used in the baseline and to confirm cases during follow-up The incidence rate ratio was calculated according to the measured characteristics and the associated factors were calculated using logistic regression models. ResultsOut of 531 workers, 9.6% tested positive for SARS-CoV-2, Being male (RR: 2.07, 95% CI: 1.1-3.8, P = .02), performing administrative tasks (RR: 1.99, 95% CI: 1.0-3.9, P = .04), and having relatives also working at INCan (RR: 3.7, 95% CI: 1.4-9.5, P < .01) were associated with higher positivity rates. DiscussionIncidence of positive cases in health workers were similar to that reported in non-COVID hospitals from other countries. ConclusionsEven though active surveillance helped to detect a significant number of asymptomatic infections, it is still necessary to reinforce preventive measures in non-medical staff to prevent nosocomial transmission.

COVID-19 Vaccination and Asymptomatic Infection: Effect of BNT162b2 mRNA Vaccine on the Incidence of COVID-19 and Duration of Sick Leave Among Healthcare Workers.

Objective:To determine the incidence of COVID-19 and the duration of sick leave among asymptomatic healthcare workers (HCWs) after vaccination with BNT162b2.Methods:From October 2020 to March 2021, we determined the incidence of COVID-19 in a cohort of 671 asymptomatic HCWs before and after the vaccination. We also analyzed the days required to obtain a negative RT-PCR result after infection.Results:Prior to vaccination 105 (15.6%) HCWs were positive. Positive cases were reduced to 42 (7.5%) after the vaccination period (P < 0.0001). A negative RT-PCR was observed at the first control in 80% of vaccinated HCWs and only in 37% before vaccination.Conclusions:Even in case of asymptomatic infection, vaccinated HCWs have a reduced incidence and a shorter period of sick leave than before vaccination, suggesting vaccination impacts on the sustainability of the health system and labor costs.

Routine Antigen Testing Is Not a Substitute for Health Care Worker Vaccination against SARS-CoV-2.

ABSTRACTThe utility of rapid antigen testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is measured within the context for which it is applied; diagnostic accuracy must be considered in determining if rapid antigen testing is appropriate for the clinical situation. In this issue of the Journal of Clinical Microbiology, J. N. Kanji, D. T. Proctor, W. Stokes, B. M. Berenger, et al. (J Clin Microbiol 59:e01411-21, 2021, https://doi.org/10.1128/JCM.01411-21) evaluate two rapid antigen tests that demonstrate high false-positive rates in asymptomatic health care workers. The assays may not be useful in situations where there is a shortage of staff, such as health care settings, since isolation would occur unnecessarily for these employees.

Association of Flu specific and SARS-CoV-2 specific CD4 T cell responses in SARS-CoV-2 infected asymptomatic heath care workers

Influenza vaccination is widely advocated to avoid infection with influenza virus, a serious respiratory pathogen, and this was greatly emphasized during the raging COVID-19 epidemic. We conducted a study for baseline Flu specific immunity in a group of health care workers with documented past SARs-CoV-2 infection (designated COVID+) with mild or no symptoms and compared them with a control group that had not been infected with SARS CoV-2 (COVID-). Concurrently, we examined flu and SARS-CoV-2 specific T cell responses using the AIM (activation induced molecules) assay by flow cytometry. All COVID+ and 40% COVID- participants exhibited AIM responses to SARS-CoV-2 peptides, but only COVID+ were positive for SARs-CoV-2 antibody. Influenza HIN1 antigen specific CD4 T cells were found in 92% COVID+ and 76% COVID- participants and exhibited a strong direct correlation with SARS-CoV-2 specific CD4 T cells. This observation suggests that influenza specific T cell immunity may impact immune responses to SARS-CoV-2.

Protracted, Intermittent Outbreak of Salmonella Mbandaka Linked to a Restaurant - Michigan, 2008-2019.

In 2018, Michigan public health officials determined that a single restaurant in southwest Michigan was the source for a protracted, intermittent outbreak of Salmonella enterica serotype Mbandaka infections occurring since 2008. Isolates from 36 infected persons shared two highly related pulsed-field gel electrophoresis (PFGE) patterns and highly related whole genome sequencing (WGS) subtypes. The initial focus of the local public health investigation on food items rather than food sources (i.e., restaurants) through a questionnaire, difficulty in food history recollection among ill persons, and sporadic case identification over periods from months to years contributed to delayed source identification. The Kalamazoo County Health and Community Services Department (KHCSD) and the Michigan Department of Health and Human Services (MDHHS) collected clinical specimens, performed multiple rounds of environmental testing, and conducted multiple regulatory visits, and based on accumulated findings over 10 years, identified the restaurant source. A 2018 investigation by KCHCSD and MDHHS found that environmental samples and stool specimens from asymptomatic restaurant employees tested positive for the Salmonella Mbandaka outbreak strain. A complex association between the restaurant environment and employees resulted in patron illnesses. Environmental health interventions, facility renovation, asymptomatic employee exclusions, employee health monitoring, and recurrent facility environmental sampling measures were implemented. As a result of ongoing cases and environmental persistence of Salmonella Mbandaka, the restaurant closed permanently in 2018. Restaurant employee stool testing and environmental sampling for Salmonella early during the investigation of confirmed Salmonella cases linked to a restaurant enhances source identification. Exclusion or restriction of asymptomatic food workers with stool-positive nontyphoidal Salmonella should be considered part of restaurant outbreak mitigation.

Development of an alternative saliva test for diagnosis of SARS-CoV-2 using TRIzol: Adapting to countries with lower incomes looking for a large-scale detection program.

The use of saliva for the diagnosis of SARS-CoV-2 has shown to be a good alternative to nasopharyngeal swabs (NPS), since it permits self-collection, avoids the exposure of healthy persons to infected patients, reduces waiting times, eliminates the need of personal protective equipment and is non-invasive. Yet current saliva testing is still expensive due to the need of specialized tubes containing buffers to stabilize the RNA of SARS-CoV-2 and inactivate the virus. These tubes are expensive and not always accessible in sufficient quantities. We now developed an alternative saliva testing method, using TRIzol for extraction, viral inactivation, and storage of SARS-CoV-2 RNA, combined with RT-qPCR, which was comparable in its performance to NPS. Paired saliva samples and NPS were taken from 15 asymptomatic healthcare workers and one patient with SARS-CoV-2. Further 13 patients with SARS-CoV-2 were only saliva-tested. All the tests were performed according to CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel. Saliva (4 mL) was taken in sterile 50 mL tubes, 1.5 mL TRIzol were added and mixed. Our results show that 5 μL of saliva RNA extracted with TRIzol allow for an adequate detection of the virus in patients positive for SARS-CoV-2 and was equally sensitive to NPS in TRIzol. We conclude that saliva testing using TRIzol is a recommendable method for diagnosis of SARS-CoV-2 since it has several advantages over currently used saliva tests: it can be done with normal sterile tubes, does not need cold-chain handling, is stable at room temperature, is non-invasive and less costly, making it more accessible for low-income countries. Cheaper saliva testing using TRIzol is especially relevant for low-income countries to optimize diagnosis and help define quarantine durations for families, healthcare workers, schools, and other public workplaces, thus decreasing infections and mortality caused by SARS-CoV-2.

Evaluation of the relationship between TREM-1/TREM-2 ratio and clinical course in COVID-19 pneumonia.

ObjectiveThe inflammatory/anti‐inflammatory balance has an important role in the clinical course of SARS‐CoV‐2 infection (COVID‐19), which has affected over 100 million people since it first appeared in China in December 2019. The aim of this study was to investigate the relationship between triggering receptor expressed on myeloid cells (TREM)‐1/TREM‐2 ratio and COVID‐19 severity.MethodsA total of 171 individuals were included in the study: 121 patients who were admitted to the chest diseases department and intensive care unit of our hospital and diagnosed with COVID‐19 by real‐time PCR of nasopharyngeal swab samples from December 2020 to March 2021 and a control group consisting of 50 asymptomatic health workers in our hospital who had negative real‐time PCR results during routine COVID‐19 screening.ResultsTREM‐1 level was significantly higher in patients with severe disease compared with the moderate and control groups (P = .003, P = .001). TREM‐2 levels did not differ significantly in moderate and severe patients (P = .36) but were significantly higher in both patient groups compared with the control group (P = .001 for both). TREM‐1/TREM‐2 ratio was significantly higher in the severe patient group than in the moderate and control groups (P = .001 for both). In receiver operating characteristic curve analysis of TREM‐1/TREM‐2 ratio in patients with moderate and severe COVID‐19, the area under the curve was 0.723. Using a cut‐off value of 0.125 for TREM‐1/TREM‐2 ratio in the Youden index calculation, the sensitivity was 60% and specificity was 71%.ConclusionExperience with the positive effects of medical treatments to restore inflammatory balance in the course of COVID‐19 is steadily increasing. TREM‐1 and TREM‐2 have an important role in inflammation and may serve as biomarkers and therapeutic targets in the early treatment and follow‐up of COVID‐19.

SARS-CoV-2 screening of asymptomatic health care workers: experience of a General hospital.

Health care workers (HCWs) are at major risk to be infected by SARS-CoV-2 and transmit the virus to the patients. Furthermore, travels are a major factor in the diffusion of the virus. We report our experience regarding the screening of asymptomatic HCWs returning from holidays, following the issue of a national guideline on 08/20/2020. The organization of the occupational health department and the clinical laboratory was adapted in order to start the screening on August, 24, 2020. All HCWs tested for SARS-CoV-2 the week before and 4 weeks after the implementation of the screening were included. The mean number of tests was analyzed per working day and working week. Overall, 502 (31.4%) HCWs were tested for SARS-CoV-2 during the study period. The mean number of HCWs tested per working day was 27.1. HCWs accounted for 36.9% (n =167) and 11.2% (n =84) of the tests performed in the 1st and the 4th week following the implementation of the guidelines. The number of tests performed each week in HCWs increased by at least 20-fold after the implementation of the guidelines. No asymptomatic HCW was tested positive. Screening of asymptomatic HCWs was poorly effective in the context of low circulation of the virus. We suggest giving priority to infection prevention and control measures and screening of symptomatic subjects and asymptomatic contacts.

Seropositivity of COVID-19 among asymptomatic healthcare workers: A multi-site prospective cohort study from Northern Virginia, United States

BackgroundBecause of their direct patient contact, healthcare workers (HCW) face an unprecedented risk of exposure to COVID-19. The aim of this study was to examine incidence of COVID-19 disease among asymptomatic HCW and community participants in Northern Virginia during 6 months of follow-up. MethodsThis is a prospective cohort study that enrolled healthy HCW and residents who never had a symptomatic COVID-19 infection prior to enrolment from the community in Northern Virginia from April to November 2020. All participants were invited to enrol in study, and they were followed at 2-, and 6-months intervals. Participants were evaluated by commercial chemiluminescence SARS-CoV-2 serology assays as part of regional health system and public health surveillance program to monitor the spread of COVID-19 disease. FindingsOf a total of 1,819 asymptomatic HCW enrolled, 1,473 (96%) had data at two-months interval, and 1,323 (73%) participants had data at 6-months interval. At baseline, 21 (1.15%) were found to have prior COVID-19 exposure. At two-months interval, COVID-19 rate was 2.8% and at six months follow-up, the overall incidence rate increased to 4.8%, but was as high as 7.9% among those who belong to the youngest age group (20–29 years). Seroconversion rates in HCW were comparable to the seropositive rates in the Northern Virginia community. The overall incidence of COVID-19 in the community was 4.5%, but the estimate was higher among Hispanic ethnicity (incidence rate = 15.3%) potentially reflecting different socio-economic factors among the community participants and the HCW group. Using cross-sectional logistic regression and spatio-temporal mixed effects models, significant factors that influence the transmission rate among HCW include age, race/ethnicity, resident ZIP-code, and household exposure, but not direct patient contact. InterpretationIn Northern Virginia, the seropositive rate of COVID-19 disease among HCW was comparable to that in the community.

Validation and implementation of a direct RT-qPCR method for rapid screening of SARS-CoV-2 infection by using non-invasive saliva samples

ObjectiveTo validate and implement an optimized screening method for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA combining use of self-collected raw saliva samples, single-step heat-treated virus inactivation and RNA extraction, and direct RT-qPCR. MethodsThis was a three-phase study conducted in Barcelona (Spain) during June to October, 2020. The three phases were (1) analytical validation against standard RT-qPCR in saliva samples; (2) diagnostic validation against standard RT-qPCR using paired saliva–nasopharyngeal samples obtained from asymptomatic teenagers and adults in a sports academy; and (3) pilot screening of asymptomatic health workers in a tertiary hospital. ResultsIn phase 1, the detection yield of the new method was comparable to that of standard RT-qPCR. In phase 2, the diagnostic sensitivity and specificity values in 303 self-collected saliva samples were 95.7% (95% confidence interval 79.0–99.2%) and 100.0% (95% confidence interval 98.6–100.0%), respectively. In phase 3, only 17 (0.6%) of the saliva samples self-collected by 2709 participants without supervision were invalid. The rapid analytical workflow with the new method (up to 384 batched samples could be processed in less than 2 hours) yielded 24 (0.9%) positive results in the remaining 2692 saliva samples. Paired nasopharyngeal specimens were all positive by standard RT-qPCR. ConclusionsDirect RT-qPCR on self-collected raw saliva is a simple, rapid, and accurate method with potential to be scaled up for enhanced SARS-CoV-2 community-wide screening.