Analysis of the risk of reinfection and influencing factors of SARS-CoV-2 nucleic acid test positive individuals in Fengxian District， Shanghai， 2022

Objective To investigate reinfection or the third time infection with SARS-CoV-2 among the people tested for positive from December 2022 to January 2023 and the influencing factors through a follow-up survey on previous novel coronavirus nucleic acid positive individuals between March to May, 2022.

Methods Epidemiological data of 2 583 novel coronavirus nucleic acid test positive cases were analyzed from March to May, 2022, following a follow-up survey at the 8^th and 12^th month after the first nucleic acid test positivity. Pearson chi-square method was used to analyze the differences of reinfection and the third time infection rates among first-positive patients with different characteristics. Kaplan-Meier survival analysis and Cox regression were used to analyze the influencing factors of reinfection.

Results A total of 2 264 valid questionnaires were collected in the 8^th month after nucleic acid tested positive, with a recovery rate of 87.7% and a reinfection rate of 9.7%. The third time infection was investigated among the individuals infected twice at the 12^th month after the first nucleic acid test positivity, with a third time infection rate of 4.6%. The median interval (P₂₅, P₇₅) between reinfection and the first nucleic acid test positive for the novel coronavirus was 261 (252, 268) days and the interval (P₂₅, P₇₅) between the third time infection and reinfection was 135 (111, 157) days. Gender, age, occupation, smoking, drinking and underlying diseases were not statistically associated with the risk of reinfection (P>0.05). However, the the third time infection rate for medical staffs (20.0%) was higher than that for student /teachers (14.3%) and corporate employees (9.5%), with a statistically significant difference in the third infection rate between different occupations (P<0.05). The risk of reinfection in self-employed individual was lower than that in corporate employees (HR=0.52, 95%CI: 0.33‒0.83), and which was still lower after adjustment for gender and age. The risk of reinfection among those with underlying diseases was 1.54 times (95%CI: 1.08‒2.02) higher than those without underlying diseases, but even 1.85 times (95%CI: 1.25‒2.75) higher after adjustment for gender and age.

Conclusion Due to the constant mutation and variants of the novel coronavirus, the risk of reinfection and the third time infection is unavoidable. The presence of underlying diseases and occupation are the main factors influencing reinfection or third time infection.