The potential of SARS-CoV-2 antigen-detection tests in the screening of asymptomatic persons

ObjectivesThe aim was to assess the performance of antigen-based rapid diagnostic tests (Ag-RDTs) for SARS CoV-2 when implemented for large-scale universal screening of asymptomatic individuals.MethodsThis study was a pragmatic implementation study for universal Ag-RDT-based screening at a tertiary care hospital in Germany where patients presenting for elective procedures and selected personnel without symptoms suggestive of SARS-CoV-2 were screened with an Ag-RDT since October 2020. Test performance was calculated on an individual patient level.ResultsIn total, 49 542 RDTs were performed in 27 421 asymptomatic individuals over a duration of 5 and a half months. Out of 222 positive results, 196 underwent in-house confirmatory testing with PCR, out of which 170 were confirmed positive, indicating a positive predictive value of 86.7% (95% CI 81.2–91.1%). Negative Ag-RDTs were not routinely tested with PCR, but a total of 94 cases of false negative Ag-RDTs were detected due to PCR tests being performed within the following 5 days with a median cycle threshold value of 33 (IQR 29–35).DiscussionThis study provides evidence that Ag-RDTs can have a high diagnostic yield for transmission relevant infections with limited false positives when utilized at the point of care on asymptomatic patients and thus can be a suitable public health test for universal screening.     

Different performance of three point-of-care SARS-CoV-2 antigen detection devices in symptomatic patients and close asymptomatic contacts: a real-life study

ObjectivesPCR on nasopharyngeal exudates, the cornerstone of the detection of SARS-CoV-2, is time-consuming and commonly unavailable at primary health care centres. Detection of viral nucleocapsid antigens using lateral flow point-of-care tests is helpful for the early triage of patients who attend health care facilities.MethodsThis was a prospective study carried out in clinically suspected cases and close asymptomatic contacts who attended a primary care centre (Madrid, Spain) for SARS-CoV-2 detection. Patients were divided into three 300-patient cohorts (n = 200 symptomatic cases and n = 100 close asymptomatic contacts per cohort). Three antigen detection tests (SGTI-Flex COVID-19 Ag, Panbio COVID-19 Ag Rapid Test Device, and GSD NovaGen SARS-CoV-2 Ag Rapid Test) were used and compared. Paired nasopharyngeal exudates were obtained, one swab for PCR and the other for antigen detection. Each antigen detection test was evaluated on one cohort.ResultsAll tests showed invariably 100% specificity. Sensitivity was 68.9% (95% CI: 55.7–80; SGTI-Flex), 71.1% (95% CI: 55.6–83.6; Panbio), and 84.6% (95% CI: 72–93.1; NovaGen) in clinically suspected patients and 84.6% (95% CI: 54.5–98.1), 33.3% (95% CI: 11.8–61.6), and 55.6% (95% CI: 30.7–78.4) in close asymptomatic contacts, respectively. Sensitivity was systematically higher in samples yielding positive PCR results with Ct ≤ 20.DiscussionWe found considerable test-to-test antigen detection variations among patients with clinical suspicion of COVID-19 and close asymptomatic contacts. Negative antigen results, regardless of the test used, should be confirmed by PCR.     

Performance of laboratory diagnostics for the detection of influenza A(H1N1)v virus as correlated with the time after symptom onset and viral load

BackgroundTo diagnose influenza A(H1N1)v virus infection, accurate and rapid detection are important. However, there is scanty data on the performance of various laboratory diagnostics.ObjectiveTo compare the performance of rapid antigen test (RAT), viral culture and RT-PCR for the detection of influenza A(H1N1)v virus and to correlate their performance with the time after symptom onset and viral load.Study DesignFrom May 1, 2009 to June 25, 2009, respiratory samples were collected from 5740 individuals suspected of having influenza A(H1N1)v infection. The performance of viral culture and RT-PCR were investigated and correlated with the time after symptom onset. The sensitivity of RAT ESPLINE influenza A & B-N (Fujirebio Inc, Tokyo) was evaluated using a subset of 60 samples from patients diagnosed as having influenza A(H1N1)v infection.ResultsUsing respiratory samples from 587 patients diagnosed with influenza A(H1N1)v infection, comparison of laboratory diagnostics showed viral culture and RT-PCR gave comparable results with overall sensitivity of 93.9% and 98.1%, respectively. For RAT, when testing a subset of 60 samples collected ≤3 days following symptom onset, the sensitivity was 62%.ConclusionsAlthough viral shedding is prolonged and of higher titre in influenza A(H1N1)v infection, RAT showed a low sensitivity of 62% among patients presenting ≤3 days after symptom onset. Viral culture showed comparable performance with RT-PCR and with sensitivity better than that documented for seasonal influenza.     

Evaluation of a rapid antigen test (Panbio™ COVID-19 Ag rapid test device) for SARS-CoV-2 detection in asymptomatic close contacts of COVID-19 patients

ObjectivesThere is limited information on the performance of rapid antigen detection (RAD) tests to identify SARS-CoV-2-infected asymptomatic individuals. In this field study, we evaluated the Panbio? COVID-19 Ag Rapid Test Device (Abbott Diagnostics, Jena, Germany) for this purpose.MethodsA total of 634 individuals (355 female; median age, 37 years; range, 9–87) were enrolled. Two nasopharyngeal swabs were collected from household (n = 338) and non-household contacts (n = 296) of COVID-19 cases. RAD testing was carried out at the point of care. The RT-PCR test used was the TaqPath COVID-19 Combo Kit (Thermo Fisher Scientific, MA, USA).ResultsHousehold contacts were tested at a median of 2 days (range, 1–7) after diagnosis of the index case, whereas non-household contacts (n = 296) were tested at a median of 6 days (range, 1–7) after exposure. In total, 79 individuals (12.4%) tested positive by RT-PCR, of whom 38 (48.1%) yielded positive RAD results. The overall sensitivity and specificity of the RAD test was 48.1% (95% CI 37.4–58.9) and 100% (95% CI 99.3–100), respectively. Sensitivity was higher in household (50.8%; 95% CI 38.9–62.5) than in non-household (35.7%; 95% CI 16.3–61.2%) contacts. Individuals testing positive by RAD test were more likely (p < 0.001) to become symptomatic than their negative counterparts.DiscussionThe Panbio test displays low sensitivity in asymptomatic close contacts of COVID-19 patients, particularly in non-household contacts. Nonetheless, establishing the optimal timing for upper respiratory tract collection in this group seems imperative to pinpoint test sensitivity.     

Real-life evaluation of a rapid antigen test (DPP SARS-CoV-2 Antigen) for COVID-19 diagnosis of primary healthcare patients,in the context of the Omicron-dominant wave in Brazil

ObjectivesWe aimed to investigate the real-life performance of the rapid antigen test in the context of a primary healthcare setting, including symptomatic and asymptomatic individuals that sought diagnosis during an Omicron infection wave.MethodsWe prospectively accessed the performance of the DPP SARS-CoV-2 Antigen test in the context of an Omicron-dominant real-life setting. We evaluated 347 unselected individuals (all-comers) from a public testing centre in Brazil, performing the rapid antigen test diagnosis at point-of-care with fresh samples. The combinatory result from two distinct real-time quantitative PCR (RT-qPCR) methods was employed as a reference and 13 samples with discordant PCR results were excluded.ResultsThe assessment of the rapid test in 67 PCR-positive and 265 negative samples revealed an overall sensitivity of 80.5% (CI 95% = 69.1%–89.2%), specificity of 99.2% (CI 95% = 97.3%–99.1%) and positive/negative predictive values higher than 95%. However, we observed that the sensitivity was dependent on the viral load (sensitivity in Ct < 31 = 93.7%, CI = 82.8%–98.7%; Ct > 31 = 47.4%, CI = 24.4%–71.1%). The positive samples evaluated in the study were Omicron (BA.1/BA.1.1) by whole-genome sequencing (n = 40) and multiplex RT-qPCR (n = 17).ConclusionsAltogether, the data obtained from a real-life prospective cohort supports that the rapid antigen test sensitivity for Omicron remains high and underscores the reliability of the test for COVID-19 diagnosis in settings with high disease prevalence and limited PCR testing capability.     

Performance characteristics and utilization of rapid antigen test,DNA probe,and culture for detection of group a streptococci in an acute care clinic

Group A streptococcus (GAS) antigen testing has become a routine point-of-care (POC) test in acute care settings. Concern about performance parameters (PP) of these tests as well as inappropriate antibiotic use has resulted in various recommendations regarding diagnosis of GAS. There were two objectives in this study. The first was to evaluate the rapid GAS antigen test presently in use (Thermo BioStar, Boulder, Colo.) and the GAS Direct probe test (Gen-Probe, San Diego, Calif.) compared to culture. The second was to define the optimal use of these technologies in a large acute care pediatric clinic. A total of 520 consecutive pediatric patients presenting with symptoms of pharyngitis at any of three Lahey Clinic acute care facilities were evaluated. Pharyngeal specimens were collected using a double-swab collection device (Copan, Corona, Calif.). One swab was used for the antigen test, the second was used for the probe test, and the pledget was placed in the collection device for culture on 5% sheep blood agar, incubated for 48 h anaerobically, and subsequently placed in Todd-Hewitt broth. After discrepant analysis, sensitivity, specificity, and positive and negative predictive values were as follows: 94.8, 100, 100, and 96.9% for the probe test and 86.1, 97.1, 93.7, and 93.4% for the antigen test, respectively. Sensitivity using an enhanced culture technique was 99.4% (163 of 164). False-positive (FP) antigen results were often seen from patients previously diagnosed and/or treated for GAS. No FP results were seen with the probe test. Colony counts for the false-negative (FN) antigen tests were higher than those for the FN probe tests. Compared to culture and DNA probe, the rapid antigen test (RAT) offered a result at the time of the patient's visit, with acceptable PP when prevalence of disease is high. Follow-up testing with the RAT of GAS patients who previously tested as positive should be avoided due to increased FP results. The probe test was comparable to culture in performance. Results indicate the probe test can be used as the primary test or as a backup to negative antigen tests. The probe test offers the advantage over culture of same-day reporting of a final result but, in contrast to a POC test, necessitates follow-up communication to the patient. Preliminary data show the specificity of the probe test to be greater than that of the RAT for patients previously diagnosed with GAS.     

Diagnostic validation of two SARS-CoV-2 immunochromatographic tests in Slovenian and Croatian hospitals

AimTo diagnostically validate two point-of-care (POC) rapid antigen tests for SARS-CoV-2 by comparing their results with those of laboratory-based real-time polymerase chain reaction tests (RT-PCR).MethodsThe study enrolled 455 patients from two Slovenian and two Croatian hospitals. The NADAL COVID-19 Ag Test (Nal von Minden, Moers, Germany) and ALLTEST COVID-19 Antigen Test (Hangzhou ALLTEST Biotech Co., Ltd, Hangzhou, China) were diagnostically validated in emergency care departments of two Slovenian hospitals, while only ALLTEST COVID-19 Antigen Test was validated in two Croatian hospitals.ResultsThe antigen test results were in very good agreement with the RT-PCR results (Cohen''s Kappa between 0.747 and 0.891 for the NADAL COVID-19 and between 0.820 and 0.954 for the ALLTEST COVID-19). The NADAL COVID-19 Ag Test had the sensitivity between 66.67% and 92.31%, with a negative predictive value between 85.51% and 99.2%. The ALLTEST COVID-19 Antigen Test had the sensitivity between 81.39% and 91.11%, with a negative predictive value between 85.45% and 98.78%.ConclusionThe antigen tests are practical and reliable screening assays for SARS CoV-2 in emergency care departments. Both antigen tests can be used as screening tests to reduce the number of patients waiting for RT-PCR results. Even more, they can be used to quickly isolate COVID-19 patients and reduce hospital transmissions.

The COVID-19 pandemic has entered every pore of health care systems worldwide and endangered their functioning. An adequate COVID-19 response should entail timely testing and sufficient testing capacities (1). A major obstacle in the current fight against SARS-CoV-2 is a much greater number of patients compared with the number of real-time polymerase chain reaction (RT-PCR) tests that can be performed. Therefore, we need quick and accurate alternative tests, such as antigen detection tests, to detect the virus presence in respiratory tract samples. Antigen tests provide rapid results and can be used efficiently by trained non-laboratory personnel as point of care tests (POCT). Rapid results may help in stopping the uncontrolled virus spread in hospitals (2). The World Health Organization (WHO) has set the standards for the use of antigen tests in terms of their negative and positive predictive value and acceptable diagnostic accuracy (3). Nevertheless, most of the available antigen tests underwent only emergency use authorizations, with limited data available on clinical validations. In addition, the number of published studies on the diagnostic performance of antigen tests vs RT-PCR is still low. In this article, we present the diagnostic validation data for two POC antigen tests in two Slovenian emergency care departments (General Hospital Jesenice and General Hospital Slovenj Gradec) and two Croatian hospitals (University Hospital Merkur and University Hospital Dubrava, both in Zagreb).     

COVID diagnostics by molecular methods: A systematic review of nucleic acid based testing systems

BackgroundThe selection of appropriate kit and PCR equipment for the detection of SARS CoV-2 is critically important in view of many options available in the diagnostic market. Since last year many molecular products are available for COVID-19 diagnostics., some of these diagnostics have become commercially available for healthcare workers and clinical laboratories. However, the diagnostic technologies have specific limitations and reported several false-positive and false-negative cases, especially during the early stages of kit development and use.The current article addresses these and other relevant questions important to the medical microbiologists running or aspiring to run COVID diagnostic services using PCR and related technologies.MethodsIn this Systematic Review we follow Preferred Reporting Items for a Systematic Review and Meta-analysis of Diagnostic Test Accuracy Studies (PRISMA-DTA). A total of 258 citations retrieved, among those 77 peer reviewed articles was assessed for eligibility, and 181 studies were excluded. Based on inclusion criteria final data extraction was done.ResultsThe question of diagnostic dilemma has also been addressed in view of discordant results between assays, inter-test variability, repeat testing requirements in specific settings and inconclusive or indeterminate results. Kit efficiency was satisfactory for all assays and the estimates varied within sample types and technology. Using clinical samples, we observed some variations in detection rate between kits. Importantly, none of the assays showed cross-reactivity with other respiratory (corona) viruses, except as expected for the SARS-CoV-1 E-gene.ConclusionsWe conclude SARS CoV-2 related molecular assays differed considerably in performance. Hence we need to understand importance of molecular diagnostics test interpretation in light of the latest pandemic virus.     

Seropositivity of Anti-SARS CoV2 IgG antibodies in health care workers of an Indian tertiary care hospital during COVID-19

PurposeHealth care workers [HCW] are at a higher risk of infection SARS CoV2 infection due to frequent and close contact to patients with COVID-19.MethodsSerum samples from 500 HCW's were tested for SARS CoV2 IgG antibodies in October 2020. A questionnaire was used to collect demographic and clinical data. All these HCWs were tested for COVID-19, in 2nd week of September 2020, as a hospital policy.ResultsAnti SARS CoV2 antibodies were detected in 128/ 500 [25.6%] HCWs. A total of 195/ 500 [39%] enrolled cases had already tested positive for Covid-19 at least once in last six months by RT-PCR. Sixty eight percent of HCWs with previous COVID-19 positivity by RT- PCR tested positive for Anti SARS CoV2 antibodies, whereas only 2.76% of asymptomatic HCWs tested positive. Of 121 anti SARS-CoV-2 IgG positive persons, 70 [57.85%] had CT value ?< ?25. Low CT value and asymptomatic cases had a strong reverse statistically significant association with SARS CoV2 IgG antibody positivity.ConclusionsWe report that sero-conversion rate in HCWs is similar to that in general population suggesting that preventive practices used in hospitals are satisfactory. Cases with low viral counts in respiratory sample and asymptomatic cases have lower rate of seroconversion.     

Rapid diagnosis of influenza infection in older adults: influence on clinical care in a routine clinical setting.

BACKGROUND: Laboratory diagnosis of influenza has previously relied on viral isolation in culture. Rapid antigen tests (RATs) are now available but few studies have examined their use in older adults under routine clinical conditions. OBJECTIVES: To determine the utility of the RAT in older adults presenting to a large medical center and how test results impacted clinical care. STUDY DESIGN: Retrospective chart review of patients tested for influenza during the 2003--2004 and 2004--2005 influenza seasons. Clinical data were correlated with the results of laboratory testing. RESULTS: Eighty-four adults tested positive for influenza. Adding the results of the RAT to symptom complexes predictive of influenza significantly enhanced the ability to diagnose influenza in the acute setting. The positive predictive value of fever plus cough increased from 32% to 92% with a positive RAT. The RAT also directed appropriate antiviral therapy. 20/22 (91%) patients with a positive RAT and symptoms < or =48 h received antiviral treatment compared to only 1/12 (8%) patients with a negative RAT and a positive culture. CONCLUSIONS: Under routine clinical conditions rapid influenza testing enhances the ability to quickly diagnose influenza and can be used to guide early treatment decisions in older adults.     

Delayed Influenza Treatment in Children With False-Negative Rapid Antigen Test: A Retrospective Single-Center Study in Korea 2016–2019

BackgroundWe aimed to examine the delay in antiviral initiation in rapid antigen test (RAT) false-negative children with influenza virus infection and to explore the clinical outcomes. We additionally conducted a medical cost-benefit analysis.MethodsThis single-center, retrospective study included children (aged < 10 years) with influenza-like illness (ILI), hospitalized after presenting to the emergency department during three influenza seasons (2016–2019). RAT-false-negativity was defined as RAT-negative and polymerase chain reaction-positive cases. The turnaround time to antiviral treatment (TAT) was from the time when RAT was prescribed to the time when the antiviral was administered. The medical cost analysis by scenarios was also performed.ResultsA total of 1,430 patients were included, 7.5% were RAT-positive (n = 107) and 2.4% were RAT-false-negative (n = 20). The median TAT of RAT-false-negative patients was 52.8 hours, significantly longer than that of 4 hours in RAT-positive patients (19.2–100.1, P < 0.001). In the multivariable analysis, TAT of ≥ 24 hours was associated with a risk of severe influenza infection and the need for mechanical ventilation (odds ratio [OR], 6.8, P = 0.009 and OR, 16.2, P = 0.033, respectively). The medical cost varied from $11.7–187.3/ILI patient.ConclusionAntiviral initiation was delayed in RAT-false-negative patients. Our findings support the guideline that children with influenza, suspected of having severe or progressive infection, should be treated immediately.     

Safety and Efficacy of Tocilizumab in the Treatment of Severe Acute Respiratory Syndrome Coronavirus-2 Pneumonia: A Retrospective Cohort Study

Background: Cytokine release storm (CRS) in severe acute respiratory syndrome coronavirus-2 (SARS CoV-2) is thought to be the cause for organ damage and death which is independent of the actual viral burden. Tocilizumab (TCZ), an interleukin-6 receptor antagonist, is approved for the treatment of CRS. We describe the efficacy and safety of TCZ in SARS CoV-2 pneumonia. Methods: This retrospective study was conducted at a tertiary care hospital from April 20 2020 to May 21 2020. The primary endpoint was the cumulative incidence of a composite of either need for admission to the intensive care unit (ICU) with invasive mechanical ventilation or death. Safety outcomes included an increase in liver transaminases and/or evidence of infection. Results: A total of 20 patients received TCZ during the study period. The median age was 54 years (95% confidence interval [CI] 47–63). About 85% of the patients were male. Nearly 70% of the patients had at least one comorbidity. About 55% required ICU admission. The median duration of ICU stay was 11 days (95% CI: 3–13 days). The cumulative incidence of the requirement for mechanical ventilation, clinical improvement and mortality was 11% (95% CI: 0.03%–1%), 74% (95% CI 37%–89%) and 25% (95% CI: 11%–63%), respectively. There was no difference in outcomes according to age, gender or computed tomography severity score. Asymptomatic transaminitis was the most common drug reaction (55%), and one patient developed bacteraemia. Conclusions: TCZ is likely a safe and effective modality of treatment for improving clinical and laboratory parameters of SARS CoV-2 patients with a reduction in ICU stay and ventilatory care need.     

Asymptomatic Clostridium difficile carriage rate post-fecal microbiota transplant is low: a prospective clinical and stool assessment

ObjectivesWe aimed to assess the asymptomatic Clostridium difficile carriage rates following fecal microbiota transplantation (FMT).MethodsAll patients who underwent FMT for recurrent Clostridium difficile infection (CDI) via colonoscopy or sigmoidoscopy between June 2013 and April 2015 and had a minimum of 8-week follow-up post FMT at two tertiary care referral centres were included in the study. Patients were prospectively followed both clinically and with stool assessments for 8 weeks post FMT. Assessments occurred at 1 week and 4 weeks post FMT to assess for failure. Failure was defined as presence of diarrhoeal symptoms and a positive CDI stool test by polymerase chain reaction for toxin gene (PCR) at any time point during the 8-week follow-up period. CDI stool testing using PCR was performed at weeks 1 and 4 post FMT in asymptomatic patients as well.Results167 patients were included. Twenty-eight patients (16.7% (28/167)) were FMT failures throughout the 8-week period. At week 1, seven patients had already failed the FMT. Of the remaining 160 patients, 144 were asymptomatic, and among these, 141 were negative for C. difficile toxin gene by PCR. This resulted in an asymptomatic carriage rate of 2.1% (3/144). At week 4, 143 patients had not yet failed FMT. Of these patients 129 patients were asymptomatic and among those, 125 were negative by PCR, resulting in an asymptomatic carriage rate of 3% (3/129).ConclusionsAsymptomatic carriage after FMT is rare. This suggests that testing for cure after FMT in asymptomatic patients is not necessary.     

Diagnosis of genitalChlamydia trachomatis infection in males by cell culture and antigen detection test

Urethral Chlamydia trachomatis infection was diagnosed in 204 of 1,011 (20.2 %) male patients by cell culture, in 219 (21.7 %) by an antigen detection test consisting of a solid phase immunoassay, and in 247 (24.4 %) patients by both methods combined. The positive results of the two methods agreed for 176 patients, and both positive and negative results of the tests agreed for 940 patients (93 %). With cell culture as the reference method, the antigen detection test had a sensitivity of 86.3 %, a specificity of 94.7 %, a positive predictive value of 80.4 % and a negative predictive value of 96.5 %. It gave false negative results in 28 patients. In 43 patients the antigen detection test gave a positive result, whereas culture was negative. Thirty-nine of these males were treated with antibiotics (tetracycline or erythromycin), 19 because their consorts had a proven Chlamydia trachomatis infection, and 20 for obvious clinical and/or microscopic findings of urethritis requiring treatment. According to this analysis there were 19 probable misses by cell culture test and four true false-positives by the antigen detection test, i.e. less than 0.4 % of all patients examined. Since one-third of males with a final diagnosis of Chlamydia trachomatis infection were clinically asymptomatic efforts to control genital chlamydial infections must identify this reservoir. The antigen detection test provides an alternative diagnostic method to the more laborious and time-consuming cell culture procedure.     

Predicting Kala-Azar Disease Manifestations in Asymptomatic Patients with Latent Leishmania donovani Infection by Detection of Antibody against Recombinant K39 Antigen

Clinically visceral leishmaniasis is suspected in only a fraction of infected persons, as the majority of these may not have clinical manifestations and remain asymptomatic. There is scanty information on diagnosing latent infections and predicting disease in asymptomatic persons. We therefore carried out a study on asymptomatic contacts of patients with visceral leishmaniasis and post-kala-azar dermal leishmaniasis by using methods for detection of antibody to recombinant K39 (rK39) antigen. A total of 240 patients with leishmaniasis and 150 asymptomatic contacts were tested for anti-rK39 immunoglobulin G (IgG) and IgA antibodies. Fifty-five asymptomatic persons were found to be seropositive. These individuals were monitored every 3 months for 1 year. On follow-up, 43.9% of the asymptomatic seropositive contacts developed kala-azar within the first 3 months, and a cumulative total of 69% developed kala-azar within 1 year. The rest remained asymptomatic and self-healed the infection. The sensitivity and specificity of rK39 enzyme-linked immunosorbent assay (ELISA) and dipstick tests were 100%, while an in-house-developed latex agglutination test had 80% sensitivity. The antibody profile showed that the IgG anti-rK39 antibodies reached a titer of up to 10⁻⁶ within 6 months of infection, started declining thereafter, and completely disappeared in 2 to 3 years in successfully treated cases. Significant titers of IgA antibodies were detectable a little earlier than those of IgG antibodies and were undetectable after 6 months. The study showed that mass screening of family members and contacts by using anti-rK39 ELISA could be a highly reliable tool for early diagnosis and to plan prophylactic treatment of latently infected asymptomatic carriers to eradicate kala-azar.