Discussion:
In this 3-week COVID-19 antibody screening test, 12 staff out of 310 screened (3.8%) had been exposed to the COVID-19 infection without being aware of it. This serology surveillance reflected the actual rate of asymptomatic and non-PUI infection among the SHC healthcare worker. Many of these infections were not detected earlier because the PUI criteria were not met. Some HCW who had close contact (low-medium risk)31 with confirmed cases did not receive the PCR testing during the early days of pandemic. This is likely due to scarce resources leading to prioritization protocol as suggested by many sources.18,32
WHO estimated a 2%-3% of the world’s population tested positive for antibody response towards COVID-19.33 Applying this projected percentage to our total HCW in SHC (686 clinical staff), the estimated number of staff with IgG antibody would be 13.7. Our surveillance result showed a higher percentage of the previous infection compared to this estimation (3.8% vs. 2%). However, this comparison is a lot lower compared to the findings of a multicentre RT-PCR surveillance study conducted on mildly symptomatic HCW in the Netherlands (COVID centres)13,3.8% vs. 9.5%.
We postulated a few reasons for the discrepancy of our staff’s infection rate with the WHO and European data. Comparing to the public population, HCW have a higher risk of being exposed to infection while delivering medical care in the frontline. While the public are expected to observe a more controlled social distancing manoeuvres during the public movement restriction orders, HCW are required to travel, and hence a higher potential risk of exposure to infection. Lower rate of infection compared to the Netherlands data may be explained by the work environment, where lower staff exposure is anticipated in a non-COVID medical facility. Shorter timing of exposure to COVID-19 patients may also explain the lower risk and rate of infection.31,34 A lower prevalence of COVID-19 cases in Kuching-Samarahan in compared to Netherlands could also be the reason for less possibility of community-acquired infections.7,35 Total HCW infection from China12 or the Netherlands13 may be higher than what were reported by the two countries if their positive PCR results had been combined with positive IgG tests in asymptomatic HCW.
Statistical analysis of our study showed a significant association of IgG status with the clinical symptoms, potential exposure at the cluster area, and place of work within the cardiology department. This finding agreed with the criteria used by WHO36 and our Ministry of Health28 to consider screening persons at higher risk when they developed respiratory symptoms or had close contact with to confirmed COVID patients or cluster areas. While testing capacity is generally not meeting the needs, this finding could guide the hospital occupational safety team to prioritize screening of HCW with higher risk in the future. Another interesting observation from our study is the significant number of staff, 7(2.7%), who tested positive with IgG but reported no symptoms at all. Asymptomatic cases remained a challenge to the COVID-19 management.37 More work is needed to study other potential clinical or epidemiological factors to risk stratify this group of patient.38
Our study had two false-positive IgM results. This observation explained the importance of interpreting lateral flow immunochromatographic assay as positive, only when the result line is clearly demarcated. A false positive result can also occur due to the cross reactivity to the other coronavirus infection.21 All 14 staff from our survey were quarantined until two sets of RT-PCR tests returned negative. These positive findings in our survey highlighted the need for post antibody serological testing plan if non-COVID medical facilities wishes to conduct an antibody serology survey. The capacity to carry out RT-PCR testing with support from the relevant authority such as the ID team, needs to be established for confirmation of viral status. It is necessary to adjust staff duty roster and pre-inform all sections of a possibility of staff shortage if quarantine orders are issued once antibody screening results are positive. Staff should also ensure that proper quarantine place is available before attempting the screening test.
Our centre’s lower IgG prevalence during the peak of the pandemic in our country may be the result of effective in-hospital infection control measures. Our COVID-19 taskforce team produced a temporary infection control protocol to reduce staff’s exposure to the infection within the hospital. Elective invasive cardiology procedures, i.e., diagnostic angiogram, transcatheter aortic valve replacement, and transoesophageal echocardiography, were postponed. Patients with clinic appointments were contacted via telephone and given options to either defer their clinic consultation with auto-renewal of prescriptions or to continue clinic consultation. To prepare for potential admission and emergency catheterization of cardiac diseases with concomitant COVID-19 infection, we redesigned ward and established a dedicated cardiac catheterization laboratory team. Medical personnel who attended to patients were directed to don level II personal protective equipment (PPE) and level III PPE, in normal wards and isolation rooms, respectively. If aerosol producing procedures were unavoidable, i.e., intubation, level III PPE were to be used. Screening of cardiac cases with respiratory symptoms were done in a temporary tent as the holding bay. Suspected PUI cases were not admitted but were referred to a COVID designated hospital. Cases expressing respiratory symptoms without epidemiological links were also discussed with infectious disease specialists to risk stratify them before admission into the wards. These patients who did not fulfill the PUI criteria but with respiratory symptoms were admitted to the temporarily designated ward where level 2 PPE were imposed for every healthcare staff who manage the patients. Patients with respiratory symptoms who needed intensive coronary care were admitted to the coronary care unit’s isolation room with negative pressure.
Lower IgG prevalence also reflects the limited potential immunity among SHC healthcare workers towards COVID-19. The in-hospital infection control measurements should be continued and constantly reviewed to suit the latest trend of pandemic control. It is still uncertain whether the presence of IgG antibodies confers long-term immunity to the individual. If so, it will have several implications such as the deployment of these “immune” staff to work in high risk areas, and the prioritization of staff for immunization32 once a vaccine becomes available.