Characteristics of work-related COVID-19 in Croatian healthcare workers: a preliminary report

This study included 59 Croatian HCWs from eight of the twenty-one Croatian counties, aged 18 to 65 years, who tested SARS-CoV-2-positive and contacted their occupational physician to have their COVID-19 registered as occupational disease between 1 May 2020 and 12 November 2020. Occupational physicians assessed workplace risk by taking patient’s occupational history and suggested participation in the study if they tested SARS-CoV-2 positive.

The study was approved by the Ethics Committees of Zagreb University School of Medicine and the Institute for Medical Research and Occupational Health, Zagreb. All participants signed an informed consent.

Occupational physicians who collaborated in this study familiarised participating HCWs, who were their patients, with our online Occupational COVID-19 in Healthcare Workers Questionnaire. We compiled this questionnaire in Microsoft Forms^® and sent the link to occupational physicians via e-mail. The physicians forwarded the link to their patients. The questionnaire starts with a short study description and continues with multiple choice questions about comorbidities, symptoms during the isolation (general weakness and fatigue, elevated body temperature, decreased sense of smell and taste, nasal congestion and fusion of postnasal secretion, cough and burning throat, severe respiratory symptoms, headache, muscle and joint pain, diarrhoea), and hospitalisation due to COVID-19. The participants were also asked to fill in their name, family name, age, personal identification number, gender, and employment info in a healthcare institution at the end of the questionnaire.

The general characteristics of the study participants and the most reported comorbidities are shown in Table 1. Most (78 %) were nurses or laboratory technicians, and most (94.9 %) worked in hospitals.

Table 2 shows the self-reported occurrence of COVID-19 related symptoms, the most common of which were general weakness and fatigue (66.1 %), elevated body temperature (57.6 %), and impaired/lost sense of smell (40.7 %). The final cluster interpretation of agglomeration schedule and coefficient changes came up with three clinically significant clusters (cluster determination line between 20 and 25 squared Euclidean distance): 1) elevated body temperature with general weakness and fatigue, 2) diarrhoea, and 3) all other symptoms (Figure 1).

Figure 1

Valid responses about hospitalisation were given by 47 (79.6 %) participants, only seven of whom (14.9 %) were hospitalised. Hospitalised and non-hospitalised participants did not differ significantly in the age, job, gender, type of health care institution, or total number of comorbidities. However, significantly more participants with respiratory comorbidity (asthma and chronic obstructive pulmonary disease) were hospitalised than not (four of seven hospitalised or 57.1 % vs. one of forty non-hospitalised or 2.5 %, respectively; P=0.001). Such significant difference was not found for any other comorbidity (listed in Table 1). Differences in COVID-19 related self-reported symptoms between hospitalised and non-hospitalized HCWs were not significant, except for cough, which was more prevalent among hospitalised than non-hospitalized patients (five of seven or 71.4 % vs. six of forty or 15.0 %, respectively; P=0.015).

Most of our participants reported mild symptoms and did not need hospitalisation. Considering their age (median 45 years; IQR 36–56 years), this was quite expected. Misra-Hebert et al. (9) reported that younger HCWs who are directly exposed to COVID-19 patients have higher odds to test positive to SARS-CoV-2 but lower odds to be hospitalised over COVID-19. The median age of HCWs in that study was 39.7 years, which is similar to ours. However, these data are not entirely comparable, since their sample was over 6000 HCWs and we did not have full data about hospitalisations (12 participants did not answer that question).

Nearly half of our participants (44.6 %) reported chronic comorbidities, but two thirds of them reported hypertension, which was not found as a risk factor for severe symptoms leading to hospitalisation. Other comorbidities were rare. Participants with chronic pulmonary condition (chronic obstructive pulmonary disease and asthma) needed hospital treatment in significantly higher proportion than participants without such comorbidity. In line with that, our hospitalised participants reported cough significantly more often than non-hospitalised ones. These findings support evidence that persons with chronic pulmonary conditions are at a higher risk of developing severe forms of COVID-19 (10) and are important for assessing work ability in people with chronic pulmonary disorders whose workplaces involve high risk of SARS-CoV-2 infection. In such cases a temporary change of workplace should be considered, particularly if pulmonary disorder compromises the use of personal protective equipment.

We found three significant clusters of COVID-19 related symptoms in our participants. The first cluster includes weakness, fatigue, and elevated body temperature, which are common general symptoms of acute infection. The second cluster seems to be more COVID-19 specific with a combination of headache, muscle and joint pain, anosmia, ageusia, and respiratory symptoms (nasal secretion and congestion, burning throat, cough, shortness of breath, dyspnoea at rest, tachypnoea). The third cluster is diarrhoea alone, which points to a separate form of disease in line with other studies. Dixon et al. (11) found two clusters: one included ageusia, anosmia, and fever, the other cough, shortness of breath, and chest pain. Wise (12) found six clusters: flu-like with no fever, flu like with fever, gastrointestinal symptoms, and three clusters separating three levels of severe disease. Clusters obviously overlap between studies, but it is evident that gastrointestinal symptoms are either not there or make a separate cluster. We believe that these differences in the number of clusters is owed not only to the type and frequency of symptom reporting, but also to the choice of statistical methods in cluster determination. Anosmia is common among SARS-CoV-2 infected HCWs and is a strong predictor of infection (13). Anosmia and ageusia were reported by 30–40 % of infected hospital workers in Milan, Italy (14), which is consistent with our findings.

In line with other studies (4), we noticed that significantly more hospital nurses and laboratory technicians reported COVID-19 than physicians. These findings probably suggest a higher risk of infection among nurses. Regression analysis of mortality rates by countries and professions in one study (15) revealed that nurses got more often infected with SARS-CoV-2 and ran a significantly higher risk of death than physicians in Italy, Spain, France, and Brazil.

We also noticed that of all our participants who requested that their COVID-19 is acknowledged as occupational 95 % work in hospitals and only 5 % in primary healthcare. This is probably because in the pandemic conditions primary care HCWs have limited their contact with patients suspect of SARS-CoV-2 infection primarily to telephone or e-mail communication.

Work-related COVID-19 among Croatian HCWs is most common in hospital nurses/laboratory technicians and takes a mild form with no need for hospital treatment. Our findings support evidence that persons with chronic pulmonary conditions are at a higher risk of developing severe forms of COVID-19. Symptom clustering points to three different clinical phenotypes: general symptoms of acute infection, COVID-19 specific neurological (anosmia, ageusia) and respiratory symptoms, and diarrhoea as a separate symptom. Further cluster analysis will involve a larger sample in order to investigate differences in symptoms between hospitalised and non-hospitalised HCWs.