Characteristic of HBV nucleic acid amplification testing yields from blood donors in China

Background Nucleic acid amplification testing (NAT) for blood screening has been previously performed in some countries to determine NAT yields. The current study sought to explore the non-discriminating reactive NAT yields using individual-NAT (ID-NAT) and characteristics of HBV NAT yields through a 10-year retrospective analysis in Zhejiang, China. Methods Blood donations were analyzed using individual-NAT mode by the transcription-mediated amplification (TMA) method. Supplementary HBV serological tests were performed using chemiluminescent immunoassay, and HBV viral load assay was performed by real-time polymerase chain reaction. Follow-up studies were performed in partial donors with low HBV viral loads. Results Non-discriminating reactive NAT yields and HBV NAT yields varied in different years. The yields ranged from 853.73 per million to 2018.68 per million and 624.60 per million to 1669.50 per million, respectively. In the 476 NAT yields, 19 were probable window periods (WP), 33 probable occult hepatitis B virus infections (OBIs), 409 were confirmed OBIs and 15 were chronic HBV infections. ID-NAT results were categorized in four groups, and the findings showed that the levels of HBV DNA viral loads were different in the four different groups (χ2 = 275.02, p < 0.01). HBV viral load distribution was significantly different between anti-HBs positive and anti-HBc positive samples (χ2 = 49.429, p < 0.01). Notably, only 42.03% donors were NAT repeated positive in the 138 repeat donors’ follow up tests. Conclusion NAT screening of blood donations can reduce the risk of transfusion-transmitted HBV infections. Positive proportions of anti-HBs and anti-HBc are correlated with the HBV viral load level. However, low level of viral load donors pose risks in HBV NAT assays, and show fluctuating state for HBV viral load and leads to non-repeated NAT results during follow up studies.

Diagnostic Performance of Ag-RDTs and NAAT for SARS-CoV2 Identification in Symptomatic Patients in Catalonia

The use of rapid antigenic tests (Ag-RDTs) to diagnose a SARS-CoV-2 infection has become a common practice recently. This study aimed to evaluate performance of Abbott PanbioTM Ag-RDTs with regard to nucleic acid amplification testing (NAAT) in the early stages of the disease. A cohort of 149,026 infected symptomatic patients, reported in Catalonia from November 2020 to January 2021, was selected. The positivity rates of the two tests were compared with respect to the dates of symptom onset. Ag-RDTs presented positivity rates of 84% in the transmission phases of the disease and 31% in the pre-symptomatic period, compared to 93% and 91%, respectively, for NAAT. The detection of many false negatives with Ag-RDTs during the pre-symptomatic period demonstrates the risk of virus dissemination with this diagnostic technique if used outside the symptomatic period.

Fourth-Generation ELISA Screening of Blood Donors: A Reliable Alternative to Nucleic Acid Testing

The gold standard for HIV screening of blood donors is individual nucleic acid amplification testing (NAT). However, individual NAT testing is cost-prohibitive, especially in a resource-limited setting. The fourth-generation ELISA that detects both p24 antigen and antibody to HIV-1 and 2 has been recommended as the minimum test for HIV to enhance blood transfusion safety and can be an alternative to NAT testing in resource-limited settings. The aim was to assess the performance of a fourth-generation ELISA in use at a regional blood transfusion service using nucleic acid amplification testing on units of screened blood negative to HIV. The study was a cross-sectional study conducted at the National Blood Transfusion Service center and the Plateau State Virology Research Centre, both in Jos, Nigeria. Between August and October 2016, one thousand and eighteen voluntary blood donors were recruited consecutively and had their samples tested using fourth-generation ELISA. One thousand p24 antigen-negative samples were pooled for NAT in an aliquot of 50 samples. All the pools of fifty samples of 1,000 HIV p24 antigen-antibody negative donor blood screened by the fourth-generation ELISA tested negative for HIV RNA on nucleic acid amplification. The yield of pooled NAT for HIV after a fourth-generation ELISA screening of blood donors was found to be zero in this study, thus establishing the fourth-generation ELISA's reliability. Therefore, we recommend adopting the fourth-generation ELISA test as a minimum requirement for blood donor screening.

Estimating the false positive rate of highly automated SARS-CoV-2 nucleic acid amplification testing

Molecular testing for infectious diseases is generally both very sensitive and specific. Well-designed PCR primers rarely cross-react with other analytes, and specificities seen during test validation are often 100%. However, analytical specificities measured during validation may not reflect real-world performance across the entire testing process. Here, we use the unique environment of SARS-CoV-2 screening among otherwise well individuals to examine the false positivity rate of high throughput so-called “sample-to-answer” nucleic acid amplification testing (NAAT) on three commercial assays: the Hologic Panther Fusion®, Hologic Aptima® transcription mediated amplification (TMA), and Roche cobas® 6800. We used repetitive sampling of the same person as the gold standard to determine test specificity rather than retesting of the same sample. We examined 451 people repetitively sampled over 7 months via nasal swab, comprising 7,242 results. During the study period there were twelve positive tests (0.17%) from 9 people. Eight positive tests (0.11%, five individuals) were considered bona fide true positives based on repeat positives or outside testing and epidemiological data. One positive test had no follow-up testing or metadata and could not be adjudicated. Three positive tests (three individuals) did not repeat as positive on a subsequent collection, nor did the original positive specimen test positive on an orthogonal platform. We consider these three tests false positives and estimate the overall false positive rate of high-throughput automated, sample-to-answer NAAT testing to be approximately 0.041% (3/7242). These data help laboratorians, epidemiologists, and regulators understand specificity and positive predictive value associated with high-throughput NAAT testing.

Accuracy of antigen and nucleic acid amplification testing on saliva and naopharyngeal samples for detection of SARS-CoV-2 in ambulatory care

Background: Nasopharyngeal sampling for nucleic acid amplification testing (NAAT) is the current standard diagnostic test for of coronavirus disease 2019 (COVID-19). However, the NAAT technique is lengthy and nasopharyngeal sampling requires trained personnel. Saliva NAAT represents an interesting alternative but diagnostic performances vary widely between studies. Objective: To assess the diagnostic accuracy of a nasopharyngeal point-of-care antigen (Ag) test and of saliva NAAT for detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), as compared to nasopharyngeal NAAT. Design: Prospective participant enrollment from 19 October through 18 December 2020. Setting: Two community COVID-19 screening centers in Paris, France. Participants: 1452 ambulatory children and adults referred for SARS-CoV-2 testing. Interventions: NAAT on a saliva sample (performed with three different protocols for pre-processing, amplification and detection of SARS-CoV-2) and Ag testing on a nasopharyngeal sample. Measurements: Performance of saliva NAAT and nasopharyngeal Ag testing. Results: Overall, 129/1443 (9%) participants tested positive on nasopharyngeal NAAT (102/564 [18%] in symptomatic and 27/879 [3%] in asymptomatic participants). Sensitivity was of 94% (95% CI, 86% to 98%), 23% (CI, 14% to 35%), 94% (CI, 88% to 97%) and 96% (CI, 91% to 99%) for the nasopharyngeal Ag test and the three different protocols of saliva NAAT, respectively. Estimates of specificity were above 95% for all methods. Diagnostic accuracy was similar in symptomatic and asymptomatic individuals. Limitations: Few children (n=122, 8%) were included. Conclusion: In the ambulatory setting, diagnostic accuracy of nasopharyngeal Ag testing and of saliva NAAT seems similar to that of nasopharyngeal NAAT, subject to strict compliance with specific pre-processing and amplification protocols. Registration number: NCT04578509 Funding Sources: French Ministry of Health and the Assistance Publique-Hopitaux de Paris Foundation.

Culture obtained from urethral swab of asymptomatic men who screen positive for Neisseria gonorrhoeae by urine nucleic acid amplification testing

BackgroundIn a previous study of men attending Melbourne Sexual Health Centre who had Neisseria gonorrhoeae detected by urine Aptima Combo 2 (AC2) testing, 11% were asymptomatic. This study aimed to determine whether N. gonorrhoeae can be cultured from asymptomatic men screening positive for N. gonorrhoeae by nucleic acid amplification testing (NAAT) of urine.MethodsBetween 1 July 2017 and 31 March 2019, all men attending Melbourne Sexual Health Centre were tested for N. gonorrhoeae by AC2 testing of urine whether urethral symptoms were reported or not. NAAT-positive men were recalled and a urethral swab performed for gonococcal culture using modified Thayer-Martin media with determination of minimum inhibitory concentrations (MICs) by agar dilution.ResultsThere were 1001 cases (860 individuals) positive for N. gonorrhoeae by urine AC2: 892 (89%) reported urethral symptoms; 109 (11%) did not. Twenty-five asymptomatic cases were excluded because of antibiotic use at or following screening. Of the remaining 84 asymptomatic men, 41 (49%) had a urethral swab performed a median of 5 days after screening. Twenty-one men had urethral discharge at the return visit, 11 of whom reported the discharge at the return visit. Of the 41 men who were swabbed, 31 (76%; 95% CI 60% to 88%) were culture positive for N. gonorrhoeae. Among the 21 men who subsequently developed discharge, 19 (90%; 95% CI 70% to 99%) were culture positive. Among the 20 men who remained asymptomatic, 12 (60%; 95% CI 36% to 81%) were culture positive. MIC profiles were obtained from all isolates.ConclusionsGonorrhoea was isolated in most but not all asymptomatic men screening positive for N. gonorrhoeae by urine NAAT. Clinicians should consider performing urethral culture in such men to ensure optimal surveillance for antimicrobial resistance. Isolation of N. gonorrhoeae by culture in men without discharge indicates these are true infections with viable organisms.