key: cord-0855933-jikxejro authors: Sam, I‐Ching; Chong, Yoong Min; Tan, Chee Wah; Chan, Yoke Fun title: Low post‐pandemic wave SARS‐CoV‐2 seroprevalence in Kuala Lumpur and Selangor, Malaysia date: 2020-08-13 journal: J Med Virol DOI: 10.1002/jmv.26426 sha: bf1ad3490041f69034b6433f07e70250f143fcbd doc_id: 855933 cord_uid: jikxejro Seroprevalence studies provide a more accurate picture of coronavirus disease 2019 (COVID‐19) than PCR‐confirmed cases as antibodies can be detected in mild or asymptomatic cases who otherwise remain undiagnosed. Seroprevalence can also be used as an indicator of population immunity. This article is protected by copyright. All rights reserved. These two assays were evaluated in our laboratory with the 228 (ELISA) or 26 (sVNT) pre-pandemic serum samples as negative controls and 35 samples collected from PCR-confirmed COVID-19 patients at least 16 days post-onset of illness. Sensitivity and specificity rates for the screening ELISA were 97.1% and 88.6%, respectively. For the confirmatory sVNT assay, sensitivity and specificity rates were 100%, after increasing the inhibition cut-off from 20% to 25%, as suggested by the manufacturer after assessing background reactivity in our setting. Our two-step testing process thus utilised assays with 97% sensitivity (screening) and 100% specificity (confirmatory), exceeding the United States FDA-recommended minimum sensitivity of 90% and specificity of 95% for serology tests with emergency use authorisation. 6 Crude seroprevalence rates are reported with 95% exact binomial confidence intervals (CI) approximated with Poisson distribution. A total of 46 (7.8%) main wave and post-wave samples screened positive, of which 3 were confirmed by sVNT. Two were from the main wave (seroprevalence 0.6%; 95% CI, 0.07-2.2%) and 1 from the post-wave period (0.4%, 95% CI, 0.01-2.1%) ( Figure 1 ). Two were from males aged in their 20s with previous diagnoses of COVID-19. The third was from a 65-year-old man with a 7-day history consistent with COVID-19, who was not tested for SARS-CoV-2. As rates for the main wave and post-wave periods were similar, they were combined to give a crude seroprevalence rate of 0.5% (95% CI, 0.1-1.5%). Using 2019 age-and gender-stratified population data for Kuala Lumpur and Selangor from the Department of Statistics, Malaysia (http://pqi.stats.gov.my/searchBI.php), a direct age-standardised seroprevalence rate was calculated as 0.4% (95% CI, 0-0.93%). This study is potentially limited by bias arising from use of residual inpatients serum. However, residual serum can provide similar estimates of seroprevalence to cohort studies 7 and is a convenient option when preliminary data is needed during a lockdown. The rate may also be underestimated because antibodies may take 2 weeks to appear and may be undetectable in some mild or asymptomatic cases. The age-standardised seroprevalence of 0.4% for Kuala Lumpur and Selangor found in this study is higher than the period prevalence of confirmed cases of 0.05%. This is consistent with other seroprevalence studies revealing 6-24 times more COVID-19 infections than are reported. 8 As this was a single centre study, a more extensive Herd immunity -estimating the level required to halt the COVID-19 epidemics in affected countries Ministry of Health Malaysia. 2020. Press statement from the Director-General of COVID-19) situation in Malaysia Serological differentiation between COVID-19 and SARS infections A SARS-CoV-2 surrogate virus neutralization test (sVNT) based on antibody-mediated blockage of ACE2-spike This article is protected by copyright. All rights reserved. Accepted Article (RBD) protein-protein interaction Evaluation of serological tests for SARS-CoV-2: Implications for serology testing in a low-prevalence setting Food & Drug Administration The age-specific cumulative incidence of infection with pandemic influenza H1N1 2009 was similar in various countries prior to vaccination Figure legend FIGURE 1. Epidemic curve of COVID-19 in Malaysia in 2020 from the first reported case on January 25 to June 30. The periods of serum sampling are shown (main wave We are grateful to Professor Lin-Fa Wang, Duke-NUS Medical School, Singapore, and GenScript Biotech for providing the sVNT testing kits.