3.4 Association between co-infection and negative conversion
All patients achieved negative conversion, with the median duration of negative conversion among all COVID-19 patients was 13 days (IQR: 10-18). Moreover, it was 13 days (IQR: 10-15) in patients with bacterial co-infection, as well as 10 days (IQR: 7.5-16.5) in patients with viral co-infection. Results from multivariate Cox regression model revealed that after controlling independent factors reported in the previous study, such as age older than 45 years and chest tightness, co-infection of other respiratory pathogens also significantly associated with negative conversion of SARS-CoV-2 RNA (Hu et al., 2020). Co-infection of only bacteria, only viruses and mixed of them were all able to promote negative conversion of COVID-19, but the promotion was different in terms of different types of co-infection. As shown in Figure 2 , the strongest promotion for negative conversion was detected with co-infection of only viruses (HR: 4.039; 95%CI: 1.238-13.177), and the weakest was found for co-infection of only bacteria (HR: 2.909; 95%CI: 1.308-6.471). Interestingly, the promotion in co-infection of mixed bacteria and viruses was between co-infection of only bacteria and only viruses, and its HR was 3.242 with 95%CI ranging from 1.171 to 8.977.