ABSTRACT
BackgroundAccurate and timely diagnosis is essential in limiting the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Real-time reverse transcription-polymerase chain reaction (rRT-PCR), the reference standard, requires specialized laboratories, costly reagents, and a long turnaround time. Antigen rapid diagnostic tests (Ag RDTs) provide a feasible alternative to rRT-PCR since they are quick, relatively inexpensive, and do not require a laboratory. The WHO requires that Ag RDTs have a sensitivity [≥]80% and specificity [≥]97%. MethodsThis evaluation was conducted at 11 health facilities in Kenya between March and July 2021. We enrolled persons of any age with respiratory symptoms and asymptomatic contacts of confirmed COVID-19 cases. We collected demographic and clinical information and two nasopharyngeal specimens from each participant for Ag RDT testing and rRT-PCR. We calculated the diagnostic performance of the Panbio Ag RDT against the US Centers for Disease Control and Preventions (CDC) rRT-PCR test. ResultsWe evaluated the Ag RDT in 2,245 individuals where 551 (24.5%, 95% CI: 22.8-26.3%) tested positive by rRT-PCR. Overall sensitivity of the Ag RDT was 46.6% (95% CI: 42.4-50.9%), specificity 98.5% (95% CI: 97.8-99.0%), PPV 90.8% (95% CI: 86.8-93.9%) and NPV 85.0% (95% CI: 83.4-86.6%). Among symptomatic individuals, sensitivity was 60.6% (95% CI: 54.3-66.7%) and specificity was 98.1% (95% CI: 96.7-99.0%). Among asymptomatic individuals, sensitivity was 34.7% (95% CI 29.3-40.4%) and specificity was 98.7% (95% CI: 97.8-99.3%). In persons with onset of symptoms <5 days (594/876, 67.8%), sensitivity was 67.1% (95% CI: 59.2-74.3%), and 53.3% (95% CI: 40.0-66.3%) among those with onset of symptoms >7 days (157/876, 17.9%). The highest sensitivity was 87.0% (95% CI: 80.9-91.8%) in symptomatic individuals with cycle threshold (Ct) values [≤]30. ConclusionThe overall sensitivity and NPV of the Panbio Ag RDT were much lower than expected. The specificity of the Ag RDT was high and satisfactory; therefore, a positive result may not require confirmation by rRT-PCR. The kit may be useful as a rapid screening tool for only symptomatic patients in high-risk settings with limited access to RT-PCR. A negative result should be interpreted based on clinical and epidemiological information and may require retesting by rRT-PCR.
ABSTRACT
<p><b>BACKGROUND</b>CD4 count is used to determine antiretroviral therapy (ART) eligibility. In China, flow cytometers are mostly located in urban areas with limited access by patients residing in remote areas. In an attempt to address this issue, we conducted a study to validate the performance of Alere PIMA point-of-care CD4 analyzer.</p><p><b>METHODS</b>Venous and finger-prick blood specimens were collected from HIV-positive participants from two voluntary counseling and testing sites in Yunnan Province. Both venous and finger-prick blood specimens were tested with the PIMA analyzer. Venous blood specimens tested with the Becton Dickinson FACSCalibur were used as a reference.</p><p><b>RESULTS</b>Venous specimens from 396 and finger-prick specimens from 387 persons were available for analysis. CD4 counts by PIMA correlated well with those from FACSCalibur with an R2 of 0.91 for venous blood and 0.81 for finger-prick blood. Compared to FACSCalibur, the PIMA analyzer yielded lower counts with a mean bias of - 47.0 cells/μl (limit of agreement, [LOA]: -204-110 cells/μl) for venous blood and -71.0 cells/μl (LOA: -295-153 cells/μl) for finger-prick blood. For a CD4 threshold of 350 cells/μl, the positive predictive value (PPV) of PIMA was 84.2% and 75.7% and the negative predictive value (NPV) was 97.6% and 95.8% for venous and finger-prick blood, respectively. For an ART threshold of 500 cells/μl, the corresponding PPV was 90.3% and 84.0% and NPV was 94.3% and 93.4%, respectively.</p><p><b>CONCLUSIONS</b>CD4 counting using venous blood with PIMA analyzers is a feasible alternative to a large flow cytometer to determine ART eligibility.</p>
