Daily use of public transportation and incidence of symptomatic COVID-19 among healthcare workers during the peak of a pandemic wave in Zurich, Switzerland

[Risk management system to reduce COVID-19 infection in health personnelSistema de gestão de riscos para reduzir o contágio de COVID-19 em profissionais de saúde]

Objective

To assess the occupational factors associated with the occurrence of COVID-19 in health personnel who were exposed to different magnitudes of risk and who followed the United Nations crisis management policy for COVID-19.

Methods

Cross-sectional survey conducted between April and May 2021. The low-risk group (LRG) were considered to be those who had minimal contact with patients; the medium-risk group (MRG) had contact with non-COVID-19 patients and did not perform instrumental airway intervention; and the high-risk group (HRG) were those who cared for COVID-19 patients and performed instrumental intervention with aerosol generation. Diagnosed COVID-19 disease and the presence of positive IgG antibodies for SARS-CoV-2 measured with Elecsys® anti-SARS-CoV-2 were considered as outcomes.

Results

Outcome recorded in 43.8% of the LRG, versus 46.7% in the MRG (odds ratio [OR]: 1.125; 95% confidence interval [CI 95% ]: 0.896-1.414; p = 0.311), and 48.6% in the HRG (OR: 1,214; CI 95%: 0.964-1.530; p= 0.10).

Conclusion

Belonging to the high-risk group and the medium-risk group, based on the degree of exposure to confirmed COVID-19 patients in the work area, was not associated with a higher occurrence of disease or seroconversion.

The emission and dynamics of droplets from human expiratory activities and COVID-19 transmission in public transport system: A review

The public transport system, containing a large number of passengers in enclosed and confined spaces, provides suitable conditions for the spread of respiratory diseases. Understanding how diseases are transmitted in public transport environment is of vital importance to public health. However, this is a highly multidisciplinary matter and the related physical processes including the emissions of respiratory droplets, the droplet dynamics and transport pathways, and subsequently, the infection risk in public transport, are poorly understood. To better grasp the complex processes involved, a synthesis of current knowledge is required. Therefore, we conducted a review on the behaviors of respiratory droplets in public transport system, covering a wide scope from the emission profiles of expiratory droplets, the droplet dynamics and transport, to the transmission of COVID-19 in public transport. The literature was searched using related keywords in Web of Science and PubMed and screened for suitability. The droplet size is a key parameter in determining the deposition and evaporation, which together with the exhaled air velocity largely determines the horizontal travel distance. The potential transmission route and transmission rate in public transport as well as the factors influencing the virus-laden droplet behaviors and virus viability (such as ventilation system, wearing personal protective equipment, air temperature and relative humidity) were also discussed. The review also suggests that future studies should address the uncertainties in droplet emission profiles associated with the measurement techniques, and preferably build a database based on a unified testing protocol. Further investigations based on field measurements and modeling studies into the influence of different ventilation systems on the transmission rate in public transport are also needed, which would provide scientific basis for controlling the transmission of diseases.