In Malaysia, the massive SARS-CoV-2 transmission started since the end of February and peaked in mid-March to mid-April 2020 (Fig. 1).[17] During this period, both medical resources and healthcare workers around the country were redirected to combat the disease. Healthcare staff from various hospitals of different departments were deployed to manage suspected and confirmed COVID-19 patients in designated healthcare facilities. This study was conducted during the post-peak period. Our finding of zero seroprevalence among asymptomatic HCW suggests that there is a low risk of asymptomatic COVID-19 infection in our healthcare setting. Another Malaysian study of 310 HCW at a non-COVID designated healthcare facility in Sarawak showed a seroprevalence rate of 4.5%, using a rapid antibody test kit, and its seroprevalence among the asymptomatic HCW was 2.7%. However, the authors reported that two study subjects with faint IgM positive results were actually false positives.[18] The sVNT used in our study is likely to have a higher specific than a rapid antibody test kit, thus reducing the risk of false positives.[19] Besides, we hypothesized HCW from designated COVID-19 hospitals would have a better perception of the potential risk of infection involved due to higher occupational exposure, which would lead to better adherence to IPC measures and reduce the transmission risk within the facility itself.
A similar study in China reported zero serological response among 420 HCW who were deployed to Wuhan during this pandemic.[20] The study coupled with our finding and suggest that appropriate PPE usage protects HCW from contracting the infection while caring for patients. However, studies conducted in other countries observed higher seroprevalence rates among HCWs. A study of 316 employees in a German tertiary hospital showed that 1.6% were seropositive for antibody against SARS-CoV-2.[21] In Kyoto, seroprevalence of anti-SARS-CoV-2 antibody among HCW were reported to be as high as 5.4%.[22] An even higher seropositivity rate was observed in an otolaryngology unit in Italy, where 5/58 (8.6%) HCW tested seropositive for IgG.[23] In a tertiary hospital in Barcelona, 45 (9.3%) out of 578 HCW were seropositive for antibody against SARS-CoV-2.[24] We postulate the discrepancy between our study and others could be multifactorial. First of all, Malaysia had a relatively low COVID-19 incidence compared to these countries during the study period. As of 17th June 2020, the incidence of COVID-19 in these countries were about 8 to 23 times higher than Malaysia, except Japan which had a lower incidence.[25] HCW seroprevalence may correlate with wider community circulation.[26, 27] Secondly, the variation of participants’ eligibility criteria between the studies may also contribute to the discrepancy. Our study focused only on asymptomatic HCW, but studies from Italy and Spain included both symptomatic HCW and those who were infected with COVID-19 previously.[23, 24] The testing method was not standardized across all studies. Any differences between the performances of each testing method can also affect the seroprevalence result.
In terms of the history of SARS-CoV-2 exposure, more than a quarter of participants claimed to have contact with known COVID-19 person outside of workplace. The participants may assume any contact with infected co-workers within hospital compound (i.e. pantry, praying area, etc.), but outside of ward as a form of contact beyond workplace. On the other hand, we observed a connection between professional categories and history of SARS-CoV-2 exposure at the workplace. This study found that doctors and nurses have more exposure to SARS-CoV-2 through all types of contact, from patients to respiratory droplets, objects and surfaces. This was in line with the nature of their work, which involves direct provision of care to patients. Laboratory technologists whose main job scope is to process patient specimens were found to have contact with patients’ body fluids most of the time.
As of early May 2020, 359 HCW from Malaysian MOH had been diagnosed with COVID-19. Of these, 73% had acquired COVID-19 from the community, including from coworkers who were infected in the community, 19% had acquired the virus from patients, and the remaining 8% were still under investigation.[28] Public fear of hospitals and HCW remains high. Many countries observed that patients have avoided seeking medical care for other health problems during this pandemic, thus resulting in late presentation with adverse outcomes.[29-32] Stigmatization and abuse of HCW has also been reported.[33-36] A study from Spain in March 2020 observed no difference in the COVID-19 infection rate of HCW by professional categories and risk of exposure in respective work departments. Other studies in Spain[24], Italy[23] and Netherlands[37] also suggested the risk to a HCW of contracting COVID-19 infection in a healthcare facility is minimal. Although our study was unable to fully rule out additional risks of COVID-19 infection in a healthcare facility, zero seroprevalence of anti-SARS-CoV-2 antibody among asymptomatic HCW should reassure the public that the risk of being infected by a HCW is very low.
Numerous studies have stressed the critical importance of strict adherence to IPC measures to prevent patient-to-HCW infections,[21, 23, 38-40] but few have investigated HCW compliance with IPC measures. Interestingly, Barrett et al. did not find any significant association between usage of PPE and COVID-19 infection rate among the HCW in United States.[41] However, our findings of high adherence to infection control guidelines and zero seroprevalence of anti-SARS-CoV-2 antibody in HCWs reinforces the importance of strict infection control and PPE usage to reduce the risk of SARS-CoV-2 transmission within healthcare facilities.
SARS-CoV-2-specific IgM and IgG antibodies start to appear during the first week of illness, and peak between two to three weeks.[42] After taking into consideration the timeline of seroconversion, serostatus of the HCW in this study most likely reflects COVID-19 transmission in Malaysia between middle of March and April 2020. This period corresponds to the second wave of COVID-19 outbreak in Malaysia following the mass religious event held in Kuala Lumpur[43], with a doubling time of confirmed COVID-19 cases ranging from two to 110 days.[44] Folgueira et al. found a close link between the driving forces of transmission in the community and HCW infection, which suggested that the rates of SARS-CoV-2 infection among HCW could be an indicator of transmission dynamics in the community.[27] If we adopt a similar principle, this study shows that the proportion of the general public in Malaysia infected as of mid-March to April could be very low, and PPE for HCW have been effective in preventing nosocomial transmission. This also signifies Malaysia’s successful public health efforts in combating this pandemic via extensive contact tracing and early admission of confirmed COVID-19 cases for isolation and close monitoring.
This study has several limitations. Firstly, this study was limited to selected healthcare facilities, so its findings may not be generalizable to HCW in other workplaces, especially non-COVID designated healthcare facilities. Secondly, we acknowledge the existence of selection bias. Participation in the study was voluntary and all participants were sampled by a non-probabilistic sampling method. HCW who refused to participate or were not sampled might be seropositive for antibody against SARS-CoV-2. As the study only recruited asymptomatic HCW, we could have potentially missed out symptomatic individuals with SARS-CoV-2 infection. Nevertheless, the literature shows that a substantial proportion of COVID-19 infected individuals can remain asymptomatic.[45-49] Thirdly, detection of anti-SARS-CoV-2 antibody in a single sample may potentially miss any SARS-CoV-2 infected HCW yet to seroconvert, although the number is likely to be minimal.