Sero-Prevalence of Covid-19 among workers in Malaysia (preprint)

From the beginning of the pandemic in Feb 2020, Malaysia has been through 4 waves of outbreak, the magnitude of each wave is several orders larger than the preceding one. By the end of the fourth wave in October 2021, Malaysia has among the highest death toll in Asia, cumulative incidence of confirmed cases has reached 7.0 percent. However it remains uncertain what is the true proportion of the population infected. We conducted a serosurvey on 1078 workers from 17 worksites in Klang Valley and Perak between July and September 2021. We tested them for SARSCoV2 specific antibodies using Ecotest, a lateral flow immunoassay. The ability of antibody testing to detect prior infection depends on the assay and seroreversion. We therefore adjusted the prevalence estimates to correct for potential misclassification bias due to the use of LFIA and seroreversion using test sensitivity and specificity results estimated from an independent validation study. The mean age of the workers was 32 years, 89 percent were male and migrant workers comprised 81 percent of all subjects, 59 percent the subjects were from Klang valley. 33 percent of workers had prior PCR confirmed Covid19 infections. We estimated 82.2 percent of workers had been infected by Covid19 by September 2021. Prevalence was 99.9 percent among migrant workers and 12.1 percent among local workers. Klang Valley, the most industrialized region in Malaysia where most migrant workers are found, had 100 percent prevalence, giving an infection to case ratio of about 3. Our seroprevalence results show that the incidence of Covid19 is extremely high among migrant workers in Malaysia, consistent with findings from other countries such as Kuwait and Singapore which also hosted large number of migrant workers.

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

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.