There is a need for reliable serological assays to determine accurate estimates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence. Most single target antigen assays have ...shown some limitations in Africa. To assess the performance of a multi-antigen assay, we evaluated a commercially available SARS-CoV-2 Multi-Antigen IgG assay for human coronavirus disease 2019 (COVID-19) in Nigeria.
Validation of the xMAP SARS-CoV-2 Multi-Antigen IgG assay was carried out using well-characterized SARS-CoV-2 reverse transcription polymerase chain reactive positive (97) and pre-COVID-19 pandemic (86) plasma panels. Cross-reactivity was assessed using pre-COVID-19 pandemic plasma specimens (213) from the 2018 Nigeria HIV/AIDS Indicator and Impact Survey (NAIIS).
The overall sensitivity of the xMAP SARS-CoV-2 Multi-Antigen IgG assay was 75.3% 95% CI: 65.8%- 82.8% and specificity was 99.0% 95% CI: 96.8%- 99.7%. The sensitivity estimate increased to 83.3% 95% CI: 70.4%- 91.3% for specimens >14 days post-confirmation of diagnosis. However, using the NAIIS pre-pandemic specimens, the false positivity rate was 1.4% (3/213).
Our results showed overall lower sensitivity and a comparable specificity with the manufacturer's validation. There appears to be less cross-reactivity with NAIIS pre-pandemic COVID-19 specimens using the xMAP SARS-CoV-2 Multi-Antigen IgG assay. In-country SARS-CoV-2 serology assay validation can help guide the best choice of assays in Africa.
Abstract
Objective
To evaluate the feasibility and performance of self-collected vaginal swab samples for HPV screening among women in Lagos, Nigeria.
Methods
A cross-sectional study was implemented ...from March to August 2020 among sexually active women. Study participants provided same-day paired vaginal swab samples. Medic-sampling and poster-directed self-sampling methods were used to collect the two samples per participant. A real-time PCR assay detected HPV 16, HPV 18, other-high-risk (OHR) HPV, and the human β-globin gene. The self-collected samples’ sensitivity, specificity, and accuracy were determined against the medic-collected samples using the MedCalc Online Diagnostic Calculator.
Results
Of the 213 women aged 16 ~ 63-year-old recruited, 187 (88%) participants had concordant results, while 26 (12%) participants had discordant results. Among the 187 concordant results, 35 (19%) were HPV positive, 150 (80%) participants were HPV negative, and two (1%) were invalid. 18 (69%) out of the 26 discordant samples were invalid. The self-collected sample was invalid for 14 (54%) participants. Two (8%) medic-collected samples were invalid. Compared to the medic-collected sample, the self-collected sample was 89.80% (95% CI: 77.77 ~ 96.60%) sensitive and 98.21% (95% CI: 94.87 ~ 99.63%) specific, with an accuracy of 96.31% (95% CI: 92.87 ~ 98.40%). The mean age for HPV positive and negative participants were 39 and 40, respectively, with an ANOVA
p
-value of 0.3932. The stratification of HPV infection by the age group was not statistically significant (
P
> 0.05).
Conclusions
With high accuracy of 96%, self-collected sampling is adequate when tested with real-time PCR and may increase the uptake of HPV testing. Though more self-collected samples were invalid than medic-collected samples, most likely due to poor collection, they could be identified for repeat testing. Future implementation can avoid this error with improved guidance and awareness.
Human Papillomavirus (HPV) infection is a risk factor for cervical cancer, the fourth most common cancer among women globally. Its burden is the highest in sub-Saharan Africa, with over 90% ...mortality. Interventions may fail without evidence-based data on stratified prevalence and risk factors among most at-risk women across Nigeria.
A cross-sectional comparative study, with participants recruited from the Nigerian Institute of Medical Research's Clinics, NGO outreaches, a cancer screening centre and a university teaching hospital. Questionnaires were self-administered. Trained medics performed sampling at healthcare facilities, and self-sampling was used at outreaches.
Nine hundred eighty-five study participants were recruited. About 37% and 27% of the women knew about HPV and its vaccines, respectively, but only 6% confirmed vaccination with HPV vaccines. HPV prevalence was highest among women with unknown marital status (35.9%), single women (33.8%), widowed/divorced/separated women (30.3%), and married/cohabiting women (19.6%). HPV infection was significantly higher among women who take alcohol (odds=1.7 95% CI: 1.2-2.4) and women who smoke (odds=2.6 95% CI: 1.4 - 4.6. HPV strains detected included HPV16 (1.3%), HPV18 (1.5%), Low Risk (0.2%) and Other High-Risk groups (19.7%).
The inverse relationship between prevalence and education suggests interventions improving awareness and prevention would be impactful. Such interventions could also target HIV-positive women, women presenting with sexually-transmitted infections, who smoke and frequently drink alcohol.
Validated assays are essential for reliable serosurveys; however, most SARS-CoV-2 immunoassays have been validated using specimens from China, Europe, or U.S. populations. We evaluated the ...performance of five commercial SARS-CoV-2 immunoassays to inform their use in serosurveys in Nigeria. Four semiquantitative enzyme-linked immunosorbent assays (ELISAs) (Euroimmun anti-SARS-CoV-2 nucleocapsid protein NCP immunoglobulin G IgG, Euroimmun spike SARS-CoV-2 IgG, Mologic Omega COVID-19 IgG, Bio-Rad Platelia SARS-CoV-2 Total Ab) and one chemiluminescent microparticle immunoassay (Abbott Architect SARS-CoV-2 IgG) were evaluated. We estimated the analytical performance characteristics using plasma from 100 SARS-CoV-2 PCR-positive patients from varied time points post-PCR confirmation and 100 prepandemic samples (50 HIV positive and 50 hepatitis B positive). The Bio-Rad assay failed the manufacturer-specified validation steps. The Euroimmun NCP, Euroimmun spike, and Mologic assays had sensitivities of 73.7%, 74.4%, and 76.9%, respectively, on samples taken 15 to 58 days after PCR confirmation and specificities of 97%, 100%, and 83.8%, respectively. The Abbott assay had 71.3% sensitivity and 100% specificity on the same panel. Parallel or serial algorithms combining two tests did not substantially improve the sensitivity or specificity. Our results showed lower sensitivity and, for one immunoassay, lower specificity compared to the manufacturers’ results and other reported validations. Seroprevalence estimates using these assays might need to be interpreted with caution in Nigeria and similar settings. These findings highlight the importance of in-country validations of SARS-CoV-2 serological assays prior to use to ensure that accurate results are available for public health decision-making to control the COVID-19 pandemic in Africa. IMPORTANCE This study used positive and negative sample panels from Nigeria to test the performance of several commercially available SARS-CoV-2 serological assays. Using these prepandemic and SARS-CoV-2-positive samples, we found much lower levels of sensitivity in four commercially available assays than most assay manufacturer reports and independent evaluations. The use of these assays with suboptimal sensitivity and specificity in Nigeria or countries with population exposure to similar endemic pathogens could lead to a biased estimate of the seroprevalence, over- or underestimating the true disease prevalence, and limit efforts to stop the spread of SARS-CoV-2. It is important to conduct in-country validations of serological SARS-CoV-2 assays prior to their widespread use, especially in countries with limited representation in published assay validations.
•In-country SARS-CoV-2 validation guide the best choice of assay for serosurvey.•Multi-antigen assays provide more accurate measures of COVID-19 seroprevalence.•Single-antigen assay may not provide ...accurate measures of COVID-19 seroprevalence.
Determining an accurate estimate of SARS-CoV-2 seroprevalence has been challenging in African countries where malaria and other pathogens are endemic. We compared the performance of one single-antigen assay and three multi-antigen SARS-CoV-2 IgG assays in a Nigerian population endemic for malaria.
De-identified plasma specimens from SARS-CoV-2 RT-PCR positive, dried blood spot (DBS) SARS-CoV-2 RT-PCR positive, and pre-pandemic negatives were used to evaluate the performance of the four SARS-CoV-2 assays (Tetracore, SARS2MBA, RightSign, xMAP).
Results showed higher sensitivity with the multi-antigen (81% (Tetracore), 96% (SARS2MBA), 85% (xMAP)) versus the single-antigen (RightSign (64%)) SARS-CoV-2 assay. The overall specificities were 98% (Tetracore), 100% (SARS2MBA and RightSign), and 99% (xMAP). When stratified based on <15 days to ≥15 days post-RT-PCR confirmation, the sensitivities increased from 75% to 88.2% for Tetracore; from 93% to 100% for the SARS2MBA; from 58% to 73% for RightSign; and from 83% to 88% for xMAP. With DBS, there was no positive increase after 15-28 days for the three assays (Tetracore, SARS2MBA, and xMAP).
Multi-antigen assays performed well in Nigeria, even with samples with known malaria reactivity, and might provide more accurate measures of COVID-19 seroprevalence and vaccine efficacy.
Accurate SARS-CoV-2 serological assays are critical for COVID-19 serosurveillance. However, previous studies have indicated possible cross-reactivity of these assays, including in areas where malaria ...is endemic. We tested 213 well-characterized prepandemic samples from Nigeria using two SARS-CoV-2 serological assays, Abbott Architect IgG and Euroimmun NCP IgG assay, both targeting SARS-CoV-2 nucleocapsid protein. To assess antibody binding strength, an avidity assay was performed on these samples and on plasma from SARS-CoV-2 PCR-positive persons. Thirteen (6.1%) of 212 samples run on the Abbott assay and 38 (17.8%) of 213 run on the Euroimmun assay were positive. Anti-
IgG levels were significantly higher among false positives for both Abbott and Euroimmun; no association was found with active Plasmodium falciparum infection. An avidity assay using various concentrations of urea wash in the Euroimmun assay reduced loosely bound IgG: of 37 positive/borderline prepandemic samples, 46%, 86%, 89%, and 97% became negative using 2 M, 4 M, 5 M, and 8 M urea washes, respectively. The wash slightly reduced avidity of antibodies from SARS-CoV-2 patients within 28 days of PCR confirmation; thereafter, avidity increased for all urea concentrations except 8 M. This validation found moderate to substantial cross-reactivity on two SARS-CoV-2 serological assays using samples from a setting where malaria is endemic. A simple urea wash appeared to alleviate issues of cross-reactivity.
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