RESUMEN
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.