Abstract Importance Several parameters driving the transmission TRANS of severe acute respiratory syndrome MESHD coronavirus 2 (SARS-CoV-2) remain unclear, including age TRANS-specific differences in infectivity and susceptibility, and the contribution of inapparent infections MESHD to transmission TRANS. Robust estimates of key time-to-event distributions remain scarce as well. Objective Illustrate SARS-CoV-2 transmission TRANS patterns and risk factors, and estimate key time-to-event distributions. Design, Setting, and Participants Individual-based data on 1,178 SARS-CoV-2 infected individuals and their 15,648 contacts identified by contact tracing TRANS monitoring over the period from January 13-April 02, 2020 were extracted from the notifiable infectious diseases MESHD reporting system in Hunan Province, China. Demographic characteristics, severity classification, exposure and travel TRANS history, and key clinical timelines were retrieved. Exposures Confirmed SARS-CoV-2 infection MESHD by positive polymerase chain reaction test result of respiratory samples, and exposure to SARS-CoV-2 infected individuals via household, relative, social, and other types of contacts. Main Outcomes and Measures The relative contribution of pre-symptomatic and asymptomatic TRANS transmission TRANS, key time-to-event parameters, and the effect of biological, demographic, and behavioral factors on SARS-CoV-2 infectivity and susceptibility were quantified. Results Among SARS-CoV-2 infected individuals, the estimated mean serial interval TRANS was 5.5 days (95%CI -5.0, 19.9) and the mean generation time was 5.5 days (95%CI 1.7, 11.6). Infectiousness was estimated to peak 1.8 days before symptom onset TRANS, with 95% of transmission TRANS events occurring between -7.6 days and 7.3 days from the date of symptom onset TRANS. The proportion of pre-symptomatic transmission TRANS was estimated at 62.5%, while a lower bound for the proportion of asymptomatic TRANS transmission TRANS was 3.5%. Infectiousness of SARS-CoV-2 was not significantly different between working- age TRANS adults TRANS (15-59 years old) and other age groups TRANS (0-14 years old: p-value=0.16; 60 years and over: p-value=0.33), whilst susceptibility to SARS-CoV-2 infection MESHD was estimated to increase with age TRANS (p-value=0.03). In addition, transmission risk TRANS was higher for household contacts TRANS (p-value<0.001), but decreased in later generations of a cluster (second generation: OR=0.13, p-value<0.001; generations 3-4: OR=0.05, p-value<0.001, relative to generation 1) and for those exposed to infectors with a larger number of contacts (p-value=0.04). Conclusions and Relevance These findings support the contribution of children TRANS to transmission TRANS and the importance of pre-symptomatic transmission TRANS, in turn highlighting the importance of large-scale testing, contact tracing TRANS activities, and the use of personnel protective equipment during the COVID-19 pandemic.