Procedures
Data were collected from October 19 to December 17, 2020. A questionnaire was first administered to participants (or their parent/guardian for those ages 5-14 years) using SurveyCTO on tablet. In this survey, which was adapted from the UNITY survey template, researchers collected information about sociodemographic factors; past COVID-19 symptoms; potential COVID-19 exposures [known contact with a laboratory-confirmed case, travel (domestic or international), and health facility use]; co-morbid conditions and other risk factors; history of health seeking behavior; and knowledge, attitudes, and beliefs about COVID-19. To asses past COVID-19-like illnesses, participants were asked whether, since the beginning of the COVID-19 pandemic in January 2020 (before the first reported case in Cameroon), they had experienced any of the following symptoms per case definition used in Cameroon: dry cough, shortness of breath, tiredness, fever, muscle pain, diarrhea, headache, new loss of smell/taste, sore throat, nausea/vomiting.
After completing the questionnaire, 5 mL of venous blood were collected and placed in a cooler box with ice packs. After providing consent, participants who decided they did not want to complete the questionnaire were still allowed to provide their blood specimens. At the end of each day, samples were transported to a local laboratory where, using the plasma preparation tubes (PPTs), they were centrifuged to separate the plasma and then immediately frozen at ‑20°C. The frozen PPTs were transported under cold chain to the National Public Health Laboratory (LNSP) at the end of each week. At LNSP, the separated plasma in each PPT was pipetted into two 1 mL cryotubes (one cryotube for each assay) and frozen at minus ‑80°C until testing was performed.
Given the expected low seroprevalence (<10%) of SARS-CoV-2 antibodies in the Cameroon population at that time a parallel testing algorithm was used to improve both the positive predictive value (PPV) and negative predictive value (NPV). Two enzyme-linked immunosorbent assays (ELISA) tests available at the time (2020) were selected based on several factors: (1) sensitivity and specificity of available tests [minimum 95% sensitivity and 90% specificity, in line with United States Food and Drug Administration Emergency Use Authorizations (US FDA EUA) validation requirements], (2) the best overall PPV and NPV of the testing algorithm using the FDA/CDC calculator on available tests on the market at that time point, (3) availability of plasma as the specimen type for testing, (4) authorization for use by US FDA EUA, WHO emergency use listing, CDC, or other internationally recognized bodies, and (5) test availability for purchase and shipment within a reasonable timeframe to complete this survey. The tests chosen were the Abbott Architect SARS-CoV-2 IgG (Abbott Diagnostics, Illinois, United States; 100% sensitivity and 99.6% specificity based on FDA report) and the WANTAI SARS-CoV-2 Ab ELISA (Beijing, China; 94.5% sensitivity and 100% specificity according to manufacturer’s report). The WANTAI assay detects total antibody to the receptor binding domain (RBD) of the SARS-CoV-2 spike protein, including IgM, IgA, and IgG antibodies, while the Abbott assay only detects IgG antibodies against the nucleocapsid (N) protein. When used in combination, this testing algorithm theoretically should produce an overall PPV of ~100% based on a prevalence from 1-10% according to the FDA PPV calculator.15
WANTAI ELISA testing was performed at the LNSP while the Abbott Architect assay was performed at the Blood Bank of Yaoundé Central Hospital because of the availability of appropriate equipment. Each assay and test interpretation was performed according to the manufacturer’s instructions and included appropriate quality controls to validate each run.16,17 After the testing was completed in the laboratory, remnant plasma specimens were returned to the -80°C freezers for long-term storage.
A call center with set operational hours was established to return the results, which was listed on the consent forms provided to the participants. Survey participants would call and obtain their test results using a random identification number assigned at enrollment.