Field evaluation of COVID‐19 antigen tests versus RNA based detection: Potential lower sensitivity compensated by immediate results, technical simplicity and low cost

Abstract Background Low- and middle-income countries (LMICs) are increasingly adopting low-cost Coronavirus disease 2019 (COVID-19) rapid antigen tests to meet the high demand for SARS-CoV-2 testing. Whilst testing using real-time polymerase chain reaction (RT-PCR) is the current gold standard, its widespread use in LMICs is limited by high costs, turnaround times and is not readily available in most places. COVID-19 antigen tests (Ag-RDT) provide a suitable alternative due to their low cost, rapid turnaround time and easy to set up and use. This study aimed to assess the field performance of the NowCheck COVID-19 antigen kit (Ag-RDT) as a point of care test (POCT) in select healthcare facilities in western Kenya. Methods We conducted a prospective multi-facility field evaluation study of the NowCheck COVID-19 rapid antigen test (Ag-RDT) compared to SARS-CoV-2 RT-PCR (RT-PCR). After obtaining informed consent, trained laboratory technicians collected two pairs of oropharyngeal and nasopharyngeal swabs, both antigen and RT-PCR testing, first for Ag-RDT and next for RT-PCR. We performed Ag-RDTs on-site and shared the results with both the study participants and their healthcare providers within 15-30 minutes. We carried out all RT-PCR tests in a central referral laboratory. The turnaround time for RT-PCR results was typically 24-48 hours. We captured the results of both methods using an electronic digital application. Findings Between December 2020 and March 2021, we enrolled 997 participants who met the Kenyan Ministry of Health COVID-19 case definition. The median age of study participants was 39 years (range one to 80 years), with 54% male. Ag-RDT had a sensitivity of 84.5% (76.0-90.8) and a specificity of 94.4% (95% CI: 92.7-95.8) with an accuracy of 94.2% (92.5- 95.6) when a cycle threshold value (Ct value) of ≤35 was used. The highest sensitivity of 87.7% (77.2-94.5) was observed in samples with Ct values ≤ 30 and the highest specificity of 97.5% (96.2-98.5) at Ct value of <40. Interpretation The NowCheck COVID-19 Ag-RDT showed good performance in field evaluation in multiple healthcare facilities in a developing country. The sensitivity of the kit exceeded the minimum recommended cut-off of 80% as recommended by WHO1. The high specificity of this kit at 94.4% at Ct values ≤33 and 97.5% at Ct values <40 matched that of real-time PCR, making it a good rule-out test for symptomatic patients with COVID-19- like symptoms. The faster turnaround time to results, lower cost, simple analytical steps requiring no equipment or infrastructure makes antigen testing an attractive field-screening method to meet the high demand for COVID-19 testing.

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Field evaluation of Rapid SARS-Cov2 Antigen screening test on self-collected deep throat saliva samples in Malaysia

10.1101/2021.12.20.21268141 ◽

2021 ◽

Author(s):

Noorliza Mohamad Noordin ◽

Chee Loon Lim ◽

Zhuo-zhi Lim ◽

Teck Onn Lim

Keyword(s):

Screening Program ◽

Low Cost ◽

False Negative ◽

Field Evaluation ◽

Contact Tracing ◽

Repeated Testing ◽

User Training ◽

The Government ◽

Antigen Tests ◽

Low Sensitivity

Low cost Rapid Antigen Tests are widely used in Malaysia and the government has also mandated worksite screening as a condition for reopening. Numerous RAT kits have been approved by the Malaysian Medical Device Authority. However, it remains uncertain how these kits would perform in the field. We enrolled workers between June and September 2021 from 23 worksites. They were trained and experienced in performing RAT selftest by virtue of their worksite participation in routine screening program. These workers also had reverse transcriptase polymerase chain reaction tests in the course of mass screening or contact tracing. We also enrolled patients with PCR confirmed Covid19 from a quarantine centre. These patients were instructed on selftesting and then immediately perform RAT under supervision. Two manufacturers donated RAT for this study. A total of 340 participants were enrolled, 130 were from quarantine centre and 210 from worksites. The overall sensitivity of RAT compared to PCR was 70 percent. The specificity was 91 percent. Sensitivity decreased with increasing PCR cycle threshold values. Sensitivity is also lower among untrained subjects at each level of Ct. Logistic regression analysis confirmed false negative result is associated with Ct and participants prior training and experience. This study shows that in the real world, RAT performance were markedly lower than that reported by the manufacturers. The test sensitivity is dependent on the operator training and experience, as well as on viral load as measured by Ct. User training and repeated testing for screening purpose is necessary to mitigate the low sensitivity of RAT.

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A portable air quality monitoring unit and a modular, flexible tool for on-field evaluation and calibration of low-cost gas sensors

HardwareX ◽

10.1016/j.ohx.2021.e00198 ◽

2021 ◽

pp. e00198

Author(s):

Domenico Suriano

Keyword(s):

Air Quality ◽

Gas Sensors ◽

Low Cost ◽

Field Evaluation ◽

Quality Monitoring ◽

Air Quality Monitoring ◽

Flexible Tool

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Calibrations of Low-Cost Air Pollution Monitoring Sensors for CO, NO2, O3, and SO2

Sensors ◽

10.3390/s21010256 ◽

2021 ◽

Vol 21 (1) ◽

pp. 256

Author(s):

Pengfei Han ◽

Han Mei ◽

Di Liu ◽

Ning Zeng ◽

Xiao Tang ◽

...

Keyword(s):

Random Forest ◽

Linear Regression ◽

Short Term Memory ◽

Hot Spot ◽

Low Cost ◽

Field Evaluation ◽

Pollution Monitoring ◽

Coefficient Of Determination ◽

Air Pollution Monitoring ◽

National Monitoring

Pollutant gases, such as CO, NO2, O3, and SO2 affect human health, and low-cost sensors are an important complement to regulatory-grade instruments in pollutant monitoring. Previous studies focused on one or several species, while comprehensive assessments of multiple sensors remain limited. We conducted a 12-month field evaluation of four Alphasense sensors in Beijing and used single linear regression (SLR), multiple linear regression (MLR), random forest regressor (RFR), and neural network (long short-term memory (LSTM)) methods to calibrate and validate the measurements with nearby reference measurements from national monitoring stations. For performances, CO > O3 > NO2 > SO2 for the coefficient of determination (R2) and root mean square error (RMSE). The MLR did not increase the R2 after considering the temperature and relative humidity influences compared with the SLR (with R2 remaining at approximately 0.6 for O3 and 0.4 for NO2). However, the RFR and LSTM models significantly increased the O3, NO2, and SO2 performances, with the R2 increasing from 0.3–0.5 to >0.7 for O3 and NO2, and the RMSE decreasing from 20.4 to 13.2 ppb for NO2. For the SLR, there were relatively larger biases, while the LSTMs maintained a close mean relative bias of approximately zero (e.g., <5% for O3 and NO2), indicating that these sensors combined with the LSTMs are suitable for hot spot detection. We highlight that the performance of LSTM is better than that of random forest and linear methods. This study assessed four electrochemical air quality sensors and different calibration models, and the methodology and results can benefit assessments of other low-cost sensors.

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60–700 K CTAT and PTAT Temperature Sensors with 4H-SiC Schottky Diodes

Sensors ◽

10.3390/s21030942 ◽

2021 ◽

Vol 21 (3) ◽

pp. 942

Author(s):

Razvan Pascu ◽

Gheorghe Pristavu ◽

Gheorghe Brezeanu ◽

Florin Draghici ◽

Philippe Godignon ◽

...

Keyword(s):

Low Cost ◽

Schottky Diodes ◽

Schottky Contact ◽

High Sensitivity ◽

Xrd Analysis ◽

Absolute Temperature ◽

Lower Sensitivity ◽

Readout Circuit ◽

Sensing Element ◽

High Performing

A SiC Schottky dual-diode temperature-sensing element, suitable for both complementary variation of VF with absolute temperature (CTAT) and differential proportional to absolute temperature (PTAT) sensors, is demonstrated over 60–700 K, currently the widest range reported. The structure’s layout places the two identical diodes in close, symmetrical proximity. A stable and high-barrier Schottky contact based on Ni, annealed at 750 °C, is used. XRD analysis evinced the even distribution of Ni2Si over the entire Schottky contact area. Forward measurements in the 60–700 K range indicate nearly identical characteristics for the dual-diodes, with only minor inhomogeneity. Our parallel diode (p-diode) model is used to parameterize experimental curves and evaluate sensing performances over this far-reaching domain. High sensitivity, upwards of 2.32 mV/K, is obtained, with satisfactory linearity (R2 reaching 99.80%) for the CTAT sensor, even down to 60 K. The PTAT differential version boasts increased linearity, up to 99.95%. The lower sensitivity is, in this case, compensated by using a high-performing, low-cost readout circuit, leading to a peak 14.91 mV/K, without influencing linearity.

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Long-term field evaluation of the Plantower PMS low-cost particulate matter sensors

Environmental Pollution ◽

10.1016/j.envpol.2018.11.065 ◽

2019 ◽

Vol 245 ◽

pp. 932-940 ◽

Cited By ~ 55

Author(s):

T. Sayahi ◽

A. Butterfield ◽

K.E. Kelly

Keyword(s):

Particulate Matter ◽

Low Cost ◽

Field Evaluation ◽

Term Field

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Assessment of SARS-CoV-2 rapid antigen tests

Journal of Laboratory Medicine ◽

10.1515/labmed-2021-0036 ◽

2021 ◽

Vol 45 (3) ◽

pp. 143-148

Author(s):

Mustafa Özcürümez ◽

Antonios Katsounas ◽

Stefan Holdenrieder ◽

Alexander von Meyer ◽

Harald Renz ◽

...

Keyword(s):

Point Of Care ◽

Low Cost ◽

Sources Of Information ◽

Package Inserts ◽

Evaluation Of Performance ◽

Specificity And Sensitivity ◽

Performance Specifications ◽

Antigen Tests ◽

Minimum Criteria ◽

Almost All

Abstract Objectives Point-of-care antigen tests (PoC-AgTs) for the rapid detection of SARS-CoV-2 infection enable screening of additional populations with less effort, independent of laboratories and at a low cost. PoC-AgTs have therefore been included in national testing strategies with additional quality requirements to address limitations in specificity and sensitivity. Information given in the package inserts of the test providers should enable the user to evaluate the performance of a PoC-AgT in advance. The quality of this information has been independently assessed since the Corona Test Ordinance came into force in Germany in October 2020. Methods The completeness of analytical and diagnostic performance specifications was assessed for all package inserts publicly available via the Paul Ehrlich Institute (PEI). It was ascertained whether the minimum criteria, recommendations, and extended criteria of the PEI were comprehensibly fulfilled. The number of tests removed from the list by March 2021 was determined. Results By the closing date of the survey (17.11.2020), the PEI had listed 165 PoC-AgTs that formally fulfilled the minimum criteria and were thus reimbursed. A total of 78 identical systems were identified. Almost all providers were found to have gaps in the information on the validation results of their tests, meaning that an evaluation of performance is only possible to a limited extent. Until March 2021, 25 non-identical PoC-AgTs have been removed from the list. Conclusions Many PoC-AgTs could not be comprehensively evaluated based on the information provided by the provider. Users are therefore dependent on provider-independent sources of information.

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Technical performance evaluation of BM/Hitachi 747-200 serum fructosamine assay

Clinical Chemistry ◽

10.1093/clinchem/42.2.244 ◽

1996 ◽

Vol 42 (2) ◽

pp. 244-248 ◽

Cited By ~ 12

Author(s):

M J Lin ◽

C Hoke ◽

B Ettinger ◽

R V Coyne

Keyword(s):

Low Cost ◽

Diabetic Control ◽

Short Term ◽

Normal Reference Range ◽

Technical Performance ◽

Hb A1c ◽

Serum Fructosamine ◽

Technical Simplicity ◽

Analytical Time

Abstract The technical performance of serum fructosamine assay as a short-term index of diabetic control was evaluated by using the BM/Hitachi 747-200 Automatic Analyzer (Boehringer Mannheim Corp). Intra- and interassay precisions (CV) were <2%. Linearity was confirmed up to 1000 micromol/L. Lipemia, produced artificially or from hypertriglyceridemia in vivo, did not interfere with measurement of serum fructosamine concentration. However, hemoglobin (Hb) interfered with measurement substantially at concentrations >15.5 micromol/L, and bilirubin interfered substantially at concentrations >68.4 micromol/L. A normal reference range of up to 282 micromol/L (mean +/- 2SD = 242 +/- 40) was derived from results obtained from 228 nondiabetic subjects. In 222 diabetic subjects, serum fructosamine concentration correlated well with fasting glucose concentration (r = 0.74) and with Hb A1c concentration (r = 0.80). This automated fructosamine assay has the advantages of technical simplicity, low cost, and reduced analytical time compared with the Hb A1c method.

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Long-term evaluation of air sensor technology under ambient conditions in Denver, Colorado

Atmospheric Measurement Techniques ◽

10.5194/amt-11-4605-2018 ◽

2018 ◽

Vol 11 (8) ◽

pp. 4605-4615 ◽

Cited By ~ 29

Author(s):

Stephen Feinberg ◽

Ron Williams ◽

Gayle S. W. Hagler ◽

Joshua Rickard ◽

Ryan Brown ◽

...

Keyword(s):

Air Pollution ◽

Wind Direction ◽

Low Cost ◽

Geographic Location ◽

Field Evaluation ◽

Time Of Day ◽

Sensor Technology ◽

Ambient Conditions ◽

Data Completeness ◽

Sampling Campaign

Abstract. Air pollution sensors are quickly proliferating for use in a wide variety of applications, with a low price point that supports use in high-density networks, citizen science, and individual consumer use. This emerging technology motivates the assessment under real-world conditions, including varying pollution levels and environmental conditions. A seven-month, systematic field evaluation of low-cost air pollution sensors was performed in Denver, Colorado, over 2015–2016; the location was chosen to evaluate the sensors in a high-altitude, cool, and dry climate. A suite of particulate matter (PM), ozone (O3), and nitrogen dioxide (NO2) sensors were deployed in triplicate and were collocated with federal equivalent method (FEM) monitors at an urban regulatory site. Sensors were evaluated for their data completeness, correlation with reference monitors, and ability to reproduce trends in pollution data, such as daily concentration values and wind-direction patterns. Most sensors showed high data completeness when data loggers were functioning properly. The sensors displayed a range of correlations with reference instruments, from poor to very high (e.g., hourly-average PM Pearson correlations with reference measurements varied from 0.01 to 0.86). Some sensors showed a change in response to laboratory audits/testing from before the sampling campaign to afterwards, such as Aeroqual, where the O3 response slope changed from about 1.2 to 0.6. Some PM sensors measured wind-direction and time-of-day trends similar to those measured by reference monitors, while others did not. This study showed different results for sensor performance than previous studies performed by the U.S. EPA and others, which could be due to different geographic location, meteorology, and aerosol properties. These results imply that continued field testing is necessary to understand emerging air sensing technology.

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The scholar seismic network of Tenerife: technical and scientific issues

10.5194/egusphere-egu2020-4796 ◽

2020 ◽

Author(s):

Vidal Domínguez ◽

José Barrancos ◽

Luca D'Auria ◽

Nemesio M. Peréz

Keyword(s):

Canary Islands ◽

Seismic Station ◽

Low Cost ◽

Seismic Network ◽

Lower Sensitivity ◽

Mems Sensors ◽

Fully Integrated ◽

Reduced Dimensions ◽

Technological Advances ◽

Didactic Material

Currently thousands of seismic sensors, managed by different national and international institutions, are deployed throughout the planet. In the last decades, thanks to scientific and technological advances, broadband sensors are being produced at costs affordable for most institutions that operate a seismic network. At the same time, advances in nanotechnology led to the development of MEMS sensors which allowed the development of accelerometers of very reduced dimensions and low costs. The seismic data obtained by the commercial MEMS sensors, can be sampled, synchronized, stored and transmitted through low cost microcontrollers such as RaspberryPi or Arduino. This allows the development of a complete seismic station of very small size and cost with respect to the traditional ones, although of lower sensitivity and quality.Since 2019, Instituto Volcanol&#243;gico de Canaria (INVOLCAN) is developing a low cost seismic network: the Red S&#237;smica Escolar Canaria (RESECAN, Scholar Canarian Seismic Network) with multiple purposes. The main aims of RESECAN are:<ul><li>supporting the teaching of geosciences</li> <li>promoting the scientific vocation</li> <li>strengthening the resilience of the Canarian communities by improving awareness of the Canary volcanism and the associated hazards.</li> </ul>The project aims at realizing and distributing low-cost stations in various educational institutions of the Canary Islands, complementing them with didactic material on the topics of seismology and volcanology. Each school will be able to access the data of its own station, as well as other centers, being able to locate some of the recorded earthquakes. The data recorded by RESECAN will be fully integrated with the data of the Red S&#237;smica Canaria (C7), a permanent broadband seismic network operated by INVOLCAN. This will make RESECAN also an instrument of scientific interest able to contribute effectively to the volcanic monitoring of the Canary Islands, strengthening its resilience in facing future volcanic emergencies.

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