Healthcare workers in Singapore infected with COVID‐19: 23 January‐17 April 2020

Abstract Objective To describe the characteristics of healthcare workers (HCWs) infected with COVID‐19 and to examine their sources of exposure. Methods A descriptive cross‐sectional study using data extracted from the centralized disease notification system comprising individuals confirmed with COVID‐19 in Singapore between 23 January and 17 April 2020. Occupation of HCWs was categorized into six categories. Their job nature was classified into “frontline” or “back‐end” based on the frequency of direct patient contact, and source of exposure was classified as family/household, social interaction or workplace. Chi‐square and median tests were used to identify differences between categorical groups and sample medians, respectively. Results A total of 88 (1.7%) HCWs were identified from 5,050 cases. Their median age was 35 years. Chinese and Indians constituted 42.0% and 31.8%, respectively, and 43.2% were foreigners. The majority (63.6%) was serving at frontlines handling patient‐facing duties, 15.9% were doctors, 11.4% were nurses and 44.3% were ancillary staff. About 81.8% acquired the infection locally, of which 40.3% did not have a clearly identifiable source of exposure. Exposure from the family/household was most common (27.8%), followed by workplace (16.7%) and social interaction (15.3%). All HCWs were discharged well with no mortality; three (3.4%) were ever admitted to intensive care unit and required increased care. Conclusion Healthcare workers accounted for a small proportion of COVID‐19 cases in Singapore with favourable outcomes. The possibility of transmission resulting from family/household exposure and social interactions highlights the need to maintain strict vigilance and precautionary measures at all times beyond the workplace.


| INTRODUC TI ON
Since the first case of coronavirus disease 2019 (COVID-19) was detected in China in December 2019, the disease has spread rapidly worldwide with an unprecedented scale of impact. The infective agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is highly contagious. One infected person may subsequently lead up to 5.7 confirmed cases. 1 Its high transmissibility has resulted in many infections and hospitalizations, even among healthcare workers (HCWs). 2 Although the case fatality rate of COVID-19 is lower than that of severe acute respiratory syndrome (SARS) (9.6%) that resulted in 8,096 cases worldwide during the eight-month outbreak in 2003, 3 COVID-19 has significantly more absolute number of fatalities. By 1 June 2020, 6.2 million of COVID-19 cases had been detected globally with case fatality rate of 6.0%. 4

Its death toll in
China was nearly three times as many people in eight weeks than that of SARS in eight months. 5 Healthcare workers are defined as paid or unpaid persons engaged in actions whose primary intent is to enhance health. 6 HCWs are at higher risk 7 of acquiring COVID-19 due to increased occupational exposure to SARS-CoV-2. In China, nearly 4% of the confirmed cases in Wuhan 8 during the initial phases of pandemic were among HCWs, due primarily to inadequate protection measures in clinical departments and shortage of personal protective equipment (PPE). 9,10 In Singapore, prior to detecting the first COVID-19 case on 23 January 2020, hospitals had already enforced the use of PPE and enhanced fever and sickness surveillance among frontline staff to protect and monitor potentially exposed HCWs. 11 Singapore reported the infection of its first HCW with COVID-19 on 13 February.
Infected HCWs are at risk of transmitting disease to vulnerable patients under their care. Knowing the details of job nature of HCWs and potential exposure to COVID-19 is crucial for risk management and prioritizing workplace crisis response plans. Healthcare institutions can identify gaps in upstream preventive measures at the workplace such as adequacy in training to handle emerging infectious diseases or adherence to standard operating procedures.
This study seeks to examine the characteristics of HCWs in Singapore who were detected to have SARS-CoV-2 between 23 January and 17 April 2020 and identify their source of exposure to prevent future infections.

| Case confirmation
Methodologies employed in case confirmation were described previously. 12

| Identifying healthcare workers
This study adopted the approach employed by the World Health Organization 6 to define HCWs. All paid workers engaged by the healthcare institutions or those whose personal actions are primarily intended to improve health but who work for non-healthcare institutions were included. 6 To better characterize HCWs, information on occupation was classified into six job categories encompassing doctor, nurse, allied health, ancillary staff, administrative staff and construction worker.
Their nature of work was broadly classified into "frontline" or "backend" based on frequency of direct patient contact required. Frontline refers to duties that directly interacted with patients, whilst backend refers to non-clinical duties with minimal to no patient contact.

| Classifying sources of infection and exposure
To ascertain the source of infection among HCWs, their exposures as collected by the contact tracing interviews were reviewed. Cases with overseas travel to countries with higher incidence of cases compared to Singapore within the past 14 days were considered imported. Cases without relevant travel history were considered locally acquired. Among the locally acquired cases, those with documented local exposure sources were classified as related to family/household, social interaction or the workplace, based on the relationships between the probable infector and infectee, where the patient with earlier symptom onset date being identified as the probable infector.
In this study, workplace exposure included both occupational exposure between HCWs and patients, and exposure to other infected HCWs within the workplace. The exposure source was classified as unidentified if the probable infector could not be determined.

| Data analysis
This is a descriptive cross-sectional study using data extracted from the centralized disease notification system. Categorical variables were analysed using number and proportions, whilst continuous measurements were described using median values. Where appropriate, between-group comparisons were conducted using chisquare and median tests to identify differences between categorical groups and sample medians, respectively, where probability less than 0.05 was considered statistically significant. Statistical Packages for Social Sciences (SPSS) v22.0 (IBM) was used for data analysis.  About 68.2% of the HCWs worked in the public sector. Of these, 83.3% worked in hospitals, 11.7% at national specialty centres and 5.0% at primary care polyclinics (    departments (Table 1). Comparatively, there were lower proportions of allied health professionals (41.7%) and frontline ancillary staff (50.0%) who worked in hospitals (Tables 2 and 3). There was a wide range of occupations among the ancillary staff, including receptionist, porter and coordinator. Healthcare assistants and porters constituted more than one-third (40.0%) of the frontline ancillary staff.

| RE SULTS
Among those working at the back-end, majority (81.3%) worked in hospitals, including 5 construction workers at hospital grounds.

| D ISCUSS I ON
During the first 86 days since the detection of Singapore's first COVID-19 case, only 1.7% of cases were HCWs. This was lower than the 2.4%-11% reported in the literature. 13   Majority of our HCWs was young with median age of 35 years, lower than 39-49 years reported in the literature. 14,18,19 The disparities could be due to the varying definitions of HCWs adopted in different studies, with many studies including only personnel who work in healthcare settings. 14,18 Our study also included HCWs who worked in non-healthcare institutions, as well as technicians and construction workers involved in hospital construction and renovation works within hospital campus. It was unclear whether these workers had been included in the literature. 14,18,19 They were primarily foreign workers who were significantly younger than the local HCWs and originated from India. Correspondingly, Indians were disproportionately higher relative to the national ethnic distribution in Singapore.
The first HCW to be detected with COVID-19 in Singapore on infector using chronological symptom onset dates could mis-specify the exposure source. There are a high proportion of cases with unidentifiable exposure source, due partially to the asymptomatic cases who did not have symptom onset date. However, they were unlikely to be linked to workplace exposure at hospital or clinics, as close contacts at the workplaces, including colleagues and patients, were tested negative for COVID-19. In Singapore, the transmission of SARS-CoV-2 during the initial phases of COVID-19 outbreak was primarily at community instead of at healthcare settings. 22 Thus, we postulated that majority of cases with unidentifiable exposure source probably acquired the virus in the community during the early phase of local spread.
In conclusion, HCWs accounted for a small proportion of all COVID-19 cases in Singapore with favourable outcomes, signalling that the existing infective control practices and measures at healthcare settings in Singapore are adequate. All HCWs, regardless of their occupation, workplace settings and working at frontline or back-end, are important human resources for medical outbreak response. To ensure sustainability of our healthcare system, all HCWs need to be protected to prevent spread to one another and to patients causing iatrogenic outbreak. The possibility of transmission resulting from family or household exposures and social interactions highlighted the need to maintain strict vigilance and precautionary measures even beyond the healthcare environment.

ACK N OWLED G EM ENTS
The authors thank Dr Wycliffe Wei for his inputs in the study.

CO N FLI C T O F I NTE R E S T S
All authors report no conflicts of interest relevant to this article.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.