Quantification of asymptomatic infections is fundamental for effective public health responses to the COVID-19 pandemic. Discrepancies regarding the extent of asymptomaticity have arisen from inconsistent terminology as well as conflation of index and secondary cases which biases toward lower asymptomaticity. We searched PubMed, Embase, Web of Science, and World Health Organization Global Research Database on COVID-19 between January 1, 2020 and April 2, 2021 to identify studies that reported silent infections at the time of testing, whether presymptomatic or asymptomatic. Index cases were removed to minimize representational bias that would result in overestimation of symptomaticity. By analyzing over 350 studies, we estimate that the percentage of infections that never developed clinical symptoms, and thus were truly asymptomatic, was 35.1% (95% CI: 30.7 to 39.9%). At the time of testing, 42.8% (95% prediction interval: 5.2 to 91.1%) of cases exhibited no symptoms, a group comprising both asymptomatic and presymptomatic infections. Asymptomaticity was significantly lower among the elderly, at 19.7% (95% CI: 12.7 to 29.4%) compared with children at 46.7% (95% CI: 32.0 to 62.0%). We also found that cases with comorbidities had significantly lower asymptomaticity compared to cases with no underlying medical conditions. Without proactive policies to detect asymptomatic infections, such as rapid contact tracing, prolonged efforts for pandemic control may be needed even in the presence of vaccination.

https://www.pnas.org/content/pnas/118/34/e2109229118.full.pdf

Asymptomatic SARS-CoV-2 infection: A systematic review and meta-analysis.

Determining the transmissibility, prevalence and patterns of movement of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections is central to our understanding of the impact of the pandemic and to the design of effective control strategies. Phylogenies (evolutionary trees) have provided key insights into the international spread of SARS-CoV-2 and enabled investigation of individual outbreaks and transmission chains in specific settings. Phylodynamic approaches combine evolutionary, demographic and epidemiological concepts and have helped track virus genetic changes, identify emerging variants and inform public health strategy. Here, we review and synthesize studies that illustrate how phylogenetic and phylodynamic techniques were applied during the first year of the pandemic, and summarize their contributions to our understanding of SARS-CoV-2 transmission and control. In this Review, the authors describe how phylogenetic and phylodynamic methods provide insight into viral evolution, focusing on the SARS-CoV-2 pandemic. The approaches reveal routes and timings of transmission events, and they can assess the effectiveness of various intervention measures aimed at controlling the virus. 

/pdf/phylogenetic-and-phylodynamic-approaches-to-understanding-245r1fim.pdf

Phylogenetic and phylodynamic approaches to understanding and combating the early SARS-CoV-2 pandemic

BACKGROUND: The dynamics of coronavirus disease 2019 (COVID-19) seroconversion of hospital employees are understudied. We measured the proportion of seroconverted employees and evaluated risk factors for seroconversion during the first pandemic wave. METHODS: In this prospective cohort study, we recruited Geneva University Hospitals employees and sampled them 3 times, every 3 weeks from March 30 to June 12, 2020. We measured the proportion of seroconverted employees and determined prevalence ratios of risk factors for seroconversion using multivariate mixed-effects Poisson regression models. RESULTS: Overall, 3,421 participants (29% of all employees) were included, with 92% follow-up. The proportion of seroconverted employees increased from 4.4% (95% confidence interval [CI], 3.7%-5.1%) at baseline to 8.5% [(95% CI, 7.6%-9.5%) at the last visit. The proportions of seroconverted employees working in COVID-19 geriatrics and rehabilitation (GR P = .006). Significant risk factors for seroconversion included the use of public transportation (adjusted prevalence ratio, 1.59; 95% CI, 1.25-2.03), known community exposure to severe acute respiratory coronavirus virus 2 (2.80; 95% CI, 2.22-3.54), working in a ward with a nosocomial COVID outbreak (2.93; 95% CI, 2.27-3.79), and working in a COVID-19 GR 95% CI, 2.45-4.91) or a non-COVID-19 GR 95% CI, 1.46-2.63). We observed an association between reported use of respirators and lower risk of seroconversion (0.73; 95% CI, 0.55-0.96). CONCLUSION: Additional preventive measures should be implemented to protect employees in G&R wards. Randomized trials on the protective effect of respirators are urgently needed.

/pdf/severe-acute-respiratory-coronavirus-virus-2-sars-cov-2-6xt95f0ida.pdf

Severe acute respiratory coronavirus virus 2 (SARS-CoV-2) seroconversion and occupational exposure of employees at a Swiss university hospital: A large longitudinal cohort study.

BACKGROUND: During the COVID-19 pandemic, most of the published reports on COVID-19 emphasized that health care workers (HCWs) get infected more than the general population representing one of the most vulnerable groups. However, that the real percentage of HCWs infected by SARS-CoV-2 in Egypt remains unknown. The researchers conducted the current study to assess seroprevalence of SARS-CoV-2 IgG among HCWs working in a hospital with no SARS-CoV-2 patients, and to identify the potential factors associated with SARS-CoV-2 IgG seropositivity. DESIGN AND METHODS: The current study is a cross-sectional study carried out among 455 HCWs at Cairo University Hospital. The researchers administered a questionnaire shortly before the SARS-CoV-2 rapid test is performed using closed-ended question format to obtain information on demographic data of the study participants including age, sex, specialty, clinical information including questions about medical conditions, and. history of previous exposure with a confirmed or suspected case of COVID-19, and history of COVID-19- compatible symptoms during the previous 14 days (cough, sore throat, runny nose, fatigue, shortness of breath, fever, headache, vomiting, diarrhea, anosmia, ageusia, and chills). RESULTS: We screened 455 HCWs for SARS-CoV-2 antibodies, 31.4% were in the high-risk group, and 68.6% in the low-risk group. The overall IgG seroprevalence was 36 (7.9%) (95% CI 5.8 to 10.8). The IgG seroprevalence was significantly higher in low-risk group 11% (35/312) versus high-risk group 0.7% (1/143), p<0.001. CONCLUSIONS: Low seropositivity rates for SARS-CoV-2 among HCWs is suggestive of lack of immunity and we are still far from herd immunity.

Asymptomatic SARS-CoV-2 infection among healthcare workers in a non-COVID-19 Teaching University Hospital.

In the backdrop of the COVID-19 pandemic, ensuring the safety of health care services remains a serious, ongoing challenge. This once-in-a-century global health crisis exposed the vulnerability of healthcare delivery systems and the subsequent risks of patient harm. Given the scale of the occurrence and costs of preventable patient safety events, intervention and investment are still relatively modest. Good patient safety governance focuses on what leaders and policy makers can do to improve system performance and reduce the financial burden of avoidable care. Moreover, it is essential in driving progress in improving safety outcomes. This report examines how patient safety governance mechanisms in OECD countries have withstood the test of COVID-19 and provides recommendations for countries in further improving patient safety governance and strengthening health system resilience. 

Advancing patient safety governance in the COVID-19 response

Asymptomatic SARS-CoV-2 infection of healthcare workers (HCWs) has been reported as a key player in the nosocomial spreading of COVID-19. Early detection of infected HCWs can prevent spreading of the virus in hospitals among HCWs and patients. We conducted a cross-sectional study to determine the asymptomatic infection of HCWs in a private clinic in the city of Santiago, Chile. Our study was conducted during a period of 5 weeks at the peak of transmission of SARS-CoV-2 in Chile. Nasopharyngeal samples were obtained from 413 HCWs and tested for the presence of SARS-CoV-2 using RT-qPCR. We found that a 3.14% of HCWs were positive for the presence of SARS-CoV-2 (14/413). Out of these, 7/14 were completely asymptomatic and did not develop symptoms within 3 weeks of testing. Sequencing of viral genomes showed the predominance of the GR clade; however, sequence comparison demonstrated numerous genetic differences among them suggesting community infection as the main focus of transmission among HCWs. Our study demonstrates that the protocols applied to protect HCWs and patients have been effective as no infection clusters due to asymptomatic carriers were found in the clinic. Together, these data suggest that infection with SARS-CoV-2 among HCWs of this health center is not nosocomial.

/pdf/sars-cov-2-infection-in-asymptomatic-healthcare-workers-at-a-1a70xvlh7x.pdf

SARS-CoV-2 infection in asymptomatic healthcare workers at a clinic in Chile.

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SARS-CoV-2 infection in asymptomatic healthcare workers at a clinic in Chile.