Background
Health-care workers (HCW) have paid a heavy toll to the coronavirus disease-19 (COVID-19) outbreak. Routes of transmission remain to be fully understood.

Methods
This prospective study compared a 1,500-bed adult and a 600-bed pediatric setting of a tertiary-care university hospital located in central Paris. From February 24^th until April 10^th, 2020, all symptomatic HCW were screened for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) on a nasopharyngeal swab. HCW screened positive were questioned on their profession, symptoms, occupational and non-occupational exposures to SARS-CoV-2.

Results
Among 1344 HCW tested, 373 were positive (28%) and 336 (90%) corresponding questionnaires were completed. Three hospitalizations and no death were reported. Most HCW (70%) had patient-facing occupational activities (22% in COVID-19 dedicated units). The total number of HCW cases peaked on March 23^rd, then decreased slowly, concomitantly with a continuous increase of compliance to preventive measures (including universal medical masking and personal protective equipment (PPE) for direct care to COVID-19 patients). Attack rates were of 3.2% and 2.3% in the adult and pediatric setting, respectively (p=0.0022). In the adult setting, HCW more frequently reported exposure to COVID-19 patients without PPE (25% versus 15%, p=0.046). Report of contacts with children attending out-of-home care facilities dramatically decreased over the study period.

Conclusion
Universal masking, reinforcement of hand hygiene, and PPE with medical masks for patients’ care allowed protection of HCW and containment of the outbreak. Residual transmissions were related to persistent exposures with undiagnosed patients or colleagues and not to contacts with children attending out-of-home care facilities.