What contributes to the re-positive nucleic acid test results for the omicron variant of SARS-CoV-2 in the shelter cabin hospital in Shanghai, China?

Background Despite the increasing reports of re-positive SARS-CoV-2 cases after recovery and discharge from hospitals, our knowledge remains very limited regarding the contributing factors of re-positivity and its roles in the transmission and epidemiology of the Omicron variant. Methods In this retrospective study, re-positivity is defined as the positive nucleic acid result (Ct < 35) following two consecutive negative results during hospitalization. A total of 751 patients from Shanghai Shelter Cabin Hospital were enrolled and divided with a ratio of about 1:2 into the re-positivity group and the non-re-positivity group. Patients required three consecutive negative results daily as the de-isolation criterion. The follow-up time of discharged patients lasted five weeks. Univariate regression analysis was used to compare variables between the re-positivity and non-re-positivity groups, and the single re-positivity and multiple re-positivity groups, with P < 0.05 defined as the statistical significance of differences. Subsequently, variables with P < 0.2 were subjected to multivariate logistic regression analysis to investigate the odds ratio (OR) of re-positivity and the influencing factors of re-positivity of the Omicron variant. Results The re-positivity group had a higher proportion of males (68.1% vs 58.1%, p = 0.000), a higher education level (31.9% vs 12.7%, p = 0.007), a longer hospitalization duration (13 days vs 8 days, p = 0.000), and a higher Convidecia vaccination rate (6.0% vs 2.4%, p = 0.011). Further multivariable analysis showed male (OR = 2.168, p = 0.000), Convidecia vaccination (OR = 2.634, p = 0.014), hospitalization duration (OR = 2.146, p = 0.000) and education level (OR = 1.595, p = 0.007) were associated with re-positivity. The average rate of re-positivity was 25% during hospitalization and decreased to 0.4% among discharged patients. Re-positivity was more common in the period with a larger number of hospitalized patients and in larger wards with a larger number of patients. Conclusion A large number of hospitalized patients, large-sized wards, and gender are significant contributing factors to re-positivity. Division of the shelter cabin hospital into small independent wards and requirement of three consecutive results daily as the de-isolation criterion might be more beneficial to the control and prevention of the spread of the Omicron variant.