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Secondary attack rate of the COVID-19

Introduction: The first case of COVID-19 infection in Kazakhstan was registered on March 13, 2020. At the beginning the detection methods and the load of the spread of the emerging respiratory pathogen were uncertain. This study aimed to assess the incidence of the secondary attack rate among close contacts of confirmed and probable COVID-19 cases living in the same household in Nur-Sultan, Kazakhstan. Methods: The prospective study included 172 participants: 122 confirmed and 50 uncertain cases of COVID-19 with varying degrees of severity as well as their close contacts identified in Nur-Sultan, Kazakhstan from November 26th, 2020 until February 15th, 2021. All participants were tested with PCR and ELISA assays at the time of inclusion and on days 14-21 of follow-up. Results: The most common symptoms among both cohorts of patients were fever (90%) (p=<0.001), cough (78.0%) (p=0.11), difficulty breathing (63.3%) (p=<0.001), chills (60%) (p=<0.001). The effective reproductive Rt number for confirmed cases was 1.43 [95%CI=1.27-1.59], for probable cases 0.96 [95%CI=0.70-1.22]. The mean serial interval was 4.02 (SD 2.52), for confirmed was 4.43 (SD 2.45), for probable cases was 3.21 (SD 2.48). Conclusion: The infection rates following close contact with COVID-19 confirmed and probable cases were 92% and 98.1%, respectively.