Performance of different rapid antigen testing strategies for SARS-CoV-2: A living rapid review

BACKGROUND

Rapid antigen detection tests (RADTs) for SARS-CoV-2 testing offer several advantages over molecular tests, but there is little evidence supporting an ideal testing algorithm. We aimed to examine the diagnostic test accuracy (DTA) and the effectiveness of different RADT SARS-CoV-2 testing strategies.

METHODS

Following PRISMA DTA guidance, we carried out a living rapid review and meta-analysis. Searches were conducted in Ovid MEDLINE® ALL, Embase and Cochrane CENTRAL electronic databases until February 2022. Results were visualized using forest plots and included in random-effects univariate meta-analyses, where eligible.

RESULTS

After screening 8010 records, 18 studies were included. Only one study provided data on incidence outcomes. Seventeen studies were DTA reports with direct comparisons of RADT strategies, using RT-PCR as the reference standard. Testing settings varied, corresponding to original SARS-CoV-2 or early variants. Strategies included differences in serial testing, the individual collecting swabs and swab sample locations. Overall, specificity remained high (>98%) across strategies. Although results were heterogeneous, the sensitivity for healthcare worker-collected samples was greater than for self-collected samples. Nasal samples had comparable sensitivity when compared to paired RADTs with nasopharyngeal samples, but sensitivity was much lower for saliva samples. The limited evidence for serial testing suggested higher sensitivity if RADTs were administered every 3 days compared to less frequent testing.

CONCLUSIONS

Additional high-quality research is needed to confirm our findings; all studies were judged to be at risk of bias, with significant heterogeneity in sensitivity estimates. Evaluations of testing algorithms in real-world settings are recommended, especially for transmission and incidence outcomes.

Extreme differences in SARS-CoV-2 viral loads among respiratory specimen types during presumed pre-infectious and infectious periods

SARS-CoV-2 viral-load measurements from a single-specimen type are used to establish diagnostic strategies, interpret clinical-trial results for vaccines and therapeutics, model viral transmission, and understand virus-host interactions. However, measurements from a single-specimen type are implicitly assumed to be representative of other specimen types. We quantified viral-load timecourses from individuals who began daily self-sampling of saliva, anterior-nares (nasal), and oropharyngeal (throat) swabs before or at the incidence of infection with the Omicron variant. Viral loads in different specimen types from the same person at the same timepoint exhibited extreme differences, up to 10⁹ copies/mL. These differences were not due to variation in sample self-collection, which was consistent. For most individuals, longitudinal viral-load timecourses in different specimen types did not correlate. Throat-swab and saliva viral loads began to rise as many as 7 days earlier than nasal-swab viral loads in most individuals, leading to very low clinical sensitivity of nasal swabs during the first days of infection. Individuals frequently exhibited presumably infectious viral loads in one specimen type while viral loads were low or undetectable in other specimen types. Therefore, defining an individual as infectious based on assessment of a single-specimen type underestimates the infectious period, and overestimates the ability of that specimen type to detect infectious individuals. For diagnostic COVID-19 testing, these three single-specimen types have low clinical sensitivity, whereas a combined throat-nasal swab, and assays with high analytical sensitivity, was inferred to have significantly better clinical sensitivity to detect presumed pre-infectious and infectious individuals.

HIV Infection Indicator Disease-Based Active Case Finding in a University Hospital: Results from the SHOT Project

In 2014, UNAIDS launched renewed global targets for HIV control to achieve by 2025, known as "the three 95": 95% of people living with HIV (PWH) diagnosed, of which 95% are receiving treatment, of which 95% are on sustained virological suppression. In Italy, new HIV diagnoses have been steadily decreasing since 2012. However, in 2020, 41% of new diagnoses presented with less than 200 CD4+ cells/µL and 60% with less than 350 CD4+ cells/µL. Implementing testing and early treatment is a key strategy to prevent AIDS, late presentation, and HIV transmission. We selected non-Infectious Diseases Units based on the European project HIDES and engaged colleagues in a condition-guided HIV screening strategy. We enrolled 300 patients, of which 202 were males (67.3%) and 98 were females (32.7%). Most of the screening was performed in Infectious Diseases (ID) and Hematologic wards. In total, we diagnosed eleven new HIV infections with a hospital prevalence in the study population of 3.7%. Five (45.4%) had a CD4 count <100/mm³, one (9.1%) <200/mm³, and one (9.1%) <300/mm³. Regarding risk factors, 81.8% declared having had unprotected sexual intercourse and 54.5% were heterosexual. All patients promptly started a combination antiretroviral regimen and 10 (90.9%) obtained an undetectable HIV-RNA status. Eight of the eleven (72.7%) patients are currently on follow-up in our outpatient clinic. A proactive indicator disease-guided screening can help avoid missed opportunities to diagnose HIV infection in a hospital setting. Implementing this kind of intervention could favor early diagnosis and access to treatment.

High Performance of SARS-Cov-2N Protein Antigen Chemiluminescence Immunoassay as Frontline Testing for Acute Phase COVID-19 Diagnosis: A Retrospective Cohort Study

Objectives: COVID-19 emerged and rapidly spread throughout the world. Testing strategies focussing on patients with COVID-19 require assays that are high-throughput, low-risk of infection, and with small sample volumes. Antigen surveillance can be used to identify exposure to pathogens and measure acute infections. Methods: A total of 914 serum samples, collected from 309 currently infected COVID-19 patients, 48 recovered ones, and 410 non-COVID-19 patients, were used to measure N protein antigen levels by a chemilumineseent immunoassay. Diagnostic performances were analyzed in different periods after onset. Results: There was a high level of N protein antigen in COVID-19 patients (0.56 COI), comparing to the recovered patients (0.12 COI) and controls (0.19 COI). In receiver-operating characteristic curve analysis, the area under the curve of serum N protein antigen was 0.911 in the first week after onset. In this period, Sensitivity and specificity of serologic N protein antigen testing was 76.27 and 98.78%. Diagnosis performance of specific antibodies became better from the third week after onset. Subgroup analysis suggested that severe patients had higher levels of antigens than mild patients. Conclusions: High level of serum antigen suggested early infection and serious illness. Serum N protein antigen testing by chemiluminescence immunoassay is considered as a viable assay used to improve diagnostic sensitivity for current patients.

Novel Hepatitic C Virus (HCV) Diagnosis and Treatment Delivery Systems: Facilitating HCV Elimination by Thinking Outside the Clinic

The World Health Organization has set a goal to eliminate hepatitis C virus (HCV) infection as public health threat by 2030. Although the advent of highly effective and tolerable direct-acting antiviral therapy has paved the way for HCV elimination, most people with HCV infection remain undiagnosed and untreated globally, with striking disparities between high-income and low- to middle-income countries. Novel decentralized and cost-effective "test-and-treat" strategies are critically needed to identify the millions of people unaware of their status and link them to treatment.

An Optimal Nucleic Acid Testing Strategy for COVID-19 during the Spring Festival Travel Rush in Mainland China: A Modelling Study

Western countries are experiencing surges in COVID-19 cases and deaths due to increasing public transportation during holiday seasons. This study aimed to explore whether mainland China will face an epidemic rebound during the Spring Festival holiday, when millions of Chinese people travel across the country, and investigate which nucleic acid testing (NAT) strategy is optimal to contain the epidemic. A microsimulation model was used to simulate SARS-CoV-2 transmission among railway travelers and evaluated the effects of various NAT strategies. An extended susceptible-exposed-infectious-recovered (SEIR) model was built to forecast local transmission during the Spring Festival period under different scenarios of testing strategies. The total number of infections, testing burden, and medical expenditure were calculated to devise an optimal strategy during the Spring Festival travel rush. Assuming the daily incidence of 20 per 10 million persons, our model simulated that there would be 97 active infections on the day of travel among 10 million railway passengers without NAT and symptom screening. Pre-travel testing could reduce the number of active infections. Compared with no NAT, testing passengers from risk tier 2-4 regions 3 days before travelling could significantly reduce the risk of transmission, and it is more economical and efficient than testing for all passengers.

Changing epidemiology of COVID-19

Background: We analyzed the epidemiology of COVID-19 in Regensburg after the first wave ended in June 2020 and compared it with patients' characteristics and symptoms in late summer/early autumn 2020. Methods: Retrospective analysis of epidemiological data from Regensburg (city/county) on age and initial symptoms as reported during case investigation for containment. Observed periods: March 7, 2020 to June 6, 2020 and August 12, 2020 to October 9, 2020. Results: The proportion of asymptomatic persons who tested positive for SARS-COV-2 in the second period was 55% (286 of 520 cases), whereas during the first wave from March to June 2020 this percentage was 14.4% (169 of 1,170 cases). A comparison of typical symptoms shows that the most common symptoms of COVID-19 in the first wave (cough, fever and generally feeling ill) were less often reported in the second period: cough 14% vs. 42%, fever 17% vs. 38%, general signs of illness 14% vs. 22% in the second vs. first period, respectively overall cases were younger in the second period, the median age of asymptomatic cases was comparable in both periods. The case fatality rate for the first period was 2.1%, in the second it was 0.2%. Discussion: The epidemiological situation in the second period is different from that during the first wave. We observed a considerable proportion of questionable cases in August/September 2020 (asymptomatic cases, high ct values, often only detection of one gene). False positive cases/non-contagious cases have to be taken into account for this period. On-demand or free-of-charge testing for asymptomatic persons will lower the positive predictive value of tests and place a high burden on finite capacities.

The need for strategic development of safety sciences

The practice of risk assessment and regulation of substances has largely developed as a patchwork of circumstantial additions to a nowadays more or less shared international toolbox. The dominant drivers from the US and Europe have pursued remarkably different approaches in the use of these tools for regulation, i.e., a more risk-based approach in the US and a more precautionary approach in Europe. We argue that there is need for scientific developments not only for the tools but also for their application, i.e., a need for Regulatory Science or, perhaps better, Safety Science. While some of this is emerging on the US side as strategic reports, e.g., from the National Academies, the NIH and the regulatory agencies, especially the EPA and the FDA, such strategic developments beyond technological developments are largely lacking in Europe or have started only recently at EFSA, ECHA or within the flagship project EU-ToxRisk. This article provides a rationale for the creation of a European Safety Sciences Institute (ESSI) based on regulatory and scientific needs, political context and current EU missions. Moreover, the possible modus operandi of ESSI will be described along with possible working formats as well as anticipated main tasks and duties. This mirrors the triple alliance on the American side (US EPA, NIH and FDA) in revamping regulatory sciences. Moreover, this could fit the political agenda of the European Commission for better implementation of existing EU legislation rather than creating new laws.

Framework to Evaluate Exposure Relevance and Data Needs for Risk Assessment of Nanomaterials using in Vitro Testing Strategies

This article presents a multistage framework for evaluating the strength of evidence of nanomaterial (NM) exposure characterization data to optimize the utility of in vitro testing strategies for human health risk assessment. This framework is intended to aid risk assessors in evaluating the relevance of data from in vitro tests and to optimize the development of new in vitro testing strategies. The initial stage frames the exposure scenarios of interest in advance of testing to incorporate aspects such as release points, route of exposure, biological and environmental transformations, dose metrics, and biological targets in subsequent stages. The second stage considers characterization in the context of a realistic exposure and the third stage involves designing a testing strategy based on expected exposure conditions. For the fourth and final stage, we propose a matrix approach to evaluate the strength of evidence obtained in the first three stages as a basis for determining the best combination of test conditions and analytical methods available to characterize and measure exposure based on the NM type. This approach can also be used to evaluate existing data for their relevance to the expected exposure scenario and to further develop and optimize in vitro testing strategies. Implementation of the proposed strategy will generate meaningful information on NM properties and their interaction with biological systems, based on realistic exposure scenarios, which will be cost effective and can be applied for assessing risk and making intelligent regulatory decisions regarding the use and disposal of NMs.

A Birth-cohort testing intervention identified hepatitis c virus infection among patients with few identified risks: a cross-sectional study

BACKGROUND

International guidelines and U.S. guidelines prior to 2012 only recommended testing for hepatitis C virus (HCV) infection among patients at risk, but adherence to guidelines is poor, and the majority of those infected remain undiagnosed. A strategy to perform one-time testing of all patients born during 1945-1965, birth cohort testing, may diagnose HCV infection among patients whose risk remains unknown. We sought to determine if a birth-cohort testing intervention for HCV antibody positivity helped identify patients with fewer documented risk factors or medical indications than a pre-intervention, risk-based testing strategy.

METHODS

We used a cross-sectional design with retrospective electronic medical record review to examine patients identified with HCV antibody positivity (Ab+) during a pre-intervention (risk-based) phase, the standard of care at the time, vs. a birth-cohort testing intervention phase. We compared demographic and clinical characteristics and HCV risk-associated factors among patients whose HCV Ab + was identified during the pre-intervention (risk-based testing) vs. post birth-cohort intervention phases. Study subjects were patients identified as HCV-Ab + in the baseline (risk-based) and birth-cohort testing phases of the Hepatitis C Assessment and Testing (HepCAT) Project.

RESULTS

Compared to the risk-based phase, patients newly diagnosed with HCV Ab + after the birth-cohort intervention were significantly less likely to have a history of any substance abuse (30.5% vs. 49.5%, p = 0.02), elevated alanine transaminase levels of > 40 U/L (22.0% vs. 46.7%, p = 0.002), or the composite any risk-associated factor (55.9% vs. 79.0%, p = 0.002).

CONCLUSIONS

Birth-cohort testing is an useful strategy for identifying previously undiagnosed HCV Ab + because it does not require providers ask risk-based questions, or patients to disclose risk behaviors, and appears to identify HCV Ab + in patients who would not have been identified using a risk-based testing strategy.

paratuberculosis

As part of a broader control strategy within herds known to be infected with Mycobacterium avium ssp. paratuberculosis (MAP), individual animal testing is generally conducted to identify infected animals for action, usually culling. Opportunities are now available to quantitatively compare different testing strategies (combinations of tests) in known infected herds. This study evaluates the effectiveness, cost, and cost-effectiveness of different testing strategies to identify infected animals at a single round of testing within dairy herds known to be MAP infected. A model was developed, taking account of both within-herd infection dynamics and test performance, to simulate the use of different tests at a single round of testing in a known infected herd. Model inputs included the number of animals at different stages of infection, the sensitivity and specificity of each test, and the costs of testing and culling. Testing strategies included either milk or serum ELISA alone or with fecal culture in series. Model outputs included effectiveness (detection fraction, the proportion of truly infected animals in the herd that are successfully detected by the testing strategy), cost, and cost-effectiveness (testing cost per true positive detected, total cost per true positive detected). Several assumptions were made: MAP was introduced with a single animal and no management interventions were implemented to limit within-herd transmission of MAP before this test. In medium herds, between 7 and 26% of infected animals are detected at a single round of testing, the former using the milk ELISA and fecal culture in series 5 yr after MAP introduction and the latter using fecal culture alone 15 yr after MAP introduction. The combined costs of testing and culling at a single round of testing increases with time since introduction of MAP infection, with culling costs being much greater than testing costs. The cost-effectiveness of testing varied by testing strategy. It was also greater at 5 yr, compared with 10 or 15 yr, since MAP introduction, highlighting the importance of early detection. Future work is needed to evaluate these testing strategies in subsequent rounds of testing as well as accounting for different herd dynamics and different levels of herd biocontainment.

Comparison of risk-based hepatitis C screening and the true seroprevalence in an urban prison system

Hepatitis C virus (HCV) is the most common blood-borne infection in the USA, though seroprevalence is elevated in certain high-risk groups such as inmates. Correctional facility screening protocols vary from universal testing to opt-in risk-based testing. This project assessed the success of a risk-based HCV screening strategy in the Philadelphia Prison System (PPS) by comparing results from current testing practices during 2011-2012 (Risk-Based Screening Group) to a September 2012 blinded seroprevalence study (Philadelphia Department of Public Health (PDPH) Study Cohort). PPS processed 51,562 inmates in 2011-2012; 2,727 were identified as high-risk and screened for HCV, of whom 57 % tested HCV antibody positive. Twelve percent (n = 154) of the 1,289 inmates in the PDPH Study Cohort were anti-HCV positive. Inmates ≥30 years of age had higher rates of seropositivity in both groups. Since only 5.3 % of the prison population was included in the Risk-Based Screening Group, an additional 4,877 HCV-positive inmates are projected to have not been identified in 2011-2012. Gaps in case identification exist when risk-based testing is utilized by PPS. A more comprehensive screening model such as opt-out universal testing should be considered to identify HCV-positive inmates. Identification of these individuals is an important opportunity to aid underserved high-risk populations and to provide medical care and secondary prevention.

Developmental toxicology: new directions workshop: refining testing strategies and study designs

In April 2009, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute's (HESI) Developmental and Reproductive Toxicology Technical Committee held a two-day workshop entitled "Developmental Toxicology-New Directions." The third session of the workshop focused on ways to refine animal studies to improve relevance and predictivity for human risk. The session included five presentations on: (1) considerations for refining developmental toxicology testing and data interpretation; (2) comparative embryology and considerations in study design and interpretation; (3) pharmacokinetic considerations in study design; (4) utility of genetically modified models for understanding mode-of-action; and (5) special considerations in reproductive testing for biologics. The presentations were followed by discussion by the presenters and attendees. Much of the discussion focused on aspects of refining current animal testing strategies, including use of toxicokinetic data, dose selection, tiered/triggered testing strategies, species selection, and use of alternative animal models. Another major area of discussion was use of non-animal-based testing paradigms, including how to define a "signal" or adverse effect, translating in vitro exposures to whole animal and human exposures, validation strategies, the need to bridge the existing gap between classical toxicology testing and risk assessment, and development of new technologies. Although there was general agreement among participants that the current testing strategy is effective, there was also consensus that traditional methods are resource-intensive and improved effectiveness of developmental toxicity testing to assess risks to human health is possible. This article provides a summary of the session's presentations and discussion and describes some key areas that warrant further consideration.