Objective: We aimed to describe the risks of health care workers (HCWs) getting COVID-19,and analyze the transmission routes and dynamics of the infection.Methods: This is a prospective observational study. We screened 624 HCWs from April 1 toMay 15, 2020, in a hospital with 300 hospital beds, in Istanbul, Turkey. All the HCWs workingat high-risk areas (COVID wards, emergency departments, and intensive care units) wereroutinely screened every four weeks. The HCWs were grouped as high, moderate, low andnone according to their risk of infection.Results: Out of 1300 total HCWs, 42 (3.2%) were diagnosed as COVID-19, 39 (3%) wereconfirmed by polymerase chain reaction (PCR) test. Among 42 symptomatic cases,26 (62%) HCWs were hospitalized, mainly because of isolation needs, 62% receivedhydroxychloroquine (HCQ) alone, 11.5% HCQ + azithromycin, and 11.5% favipiravir only. Allsurvived. We detected nine asymptomatic cases out of 550 HCWs (1.6%) in our screeningfor antibody levels. In none of the nine asymptomatic HCWs, SARS-CoV-2 RNA was notdetected by PCR. In multivariate analysis for detecting the risk factors of the SARS-CoV-2infection, working in high-risk areas (OR:5.2, CI:1.99-13.6, p=0.001), and not to use properpersonal protective equipment (PPE) (OR:5.9, CI:1.66-21.2, p=0.006) increased the risk ofinfection.Conclusion: Routine screening of asymptomatic HCWs with antibody tests might be useful,but its effectiveness was limited. The HCWs working in high-risk areas had significantlyhigher risk. The strict use of appropriate PPE was effective in prevention.