Study description
The COVID-19 outbreak was first reported in Wuhan [6] and lasted for more than 3 months; after May 18, 2020, there were no further locally acquired infections. During the outbreak in Wuhan, there were 50,340 confirmed COVID-19 cases, with 3869 deaths, and 46,471 patients were clinically cured and discharged in accordance with the WHO guidelines [7]. After being discharged from the hospital, patients in Wuhan continued to isolate in a rehabilitation center for 14 days and at home for another 14 days to prevent reinfection. These patients were regularly followed up through hospital visits. Here, the information from 118 hospitals in Wuhan on COVID-19 patients who had a positive SARS-CoV-2 PCR test between December 31, 2019, and August 4, 2020, was collected from the surveillance network of Wuhan Center for Disease Control and Prevention (Supplementary Table 1 for the names of hospitals) and performed a retrospective analysis to ascertain the epidemiological and clinical features of those with a re-positive test. Due to privacy concerns, data cannot be made openly available. For further information about the data, please contact Wuhan Center for Disease Control and Prevention.
Data collection
COVID-19 diagnosis and illness severity was defined in accordance with the Chinese management guidelines for COVID-19 published by the National Health Commission of the People’s Republic of China. All first diagnoses of COVID-19 and all re-positive cases were confirmed by a reverse transcriptase-polymerase chain reaction (RT-PCR) test of nasopharyngeal swab or pharynx swab samples. The samples were collected and tested for SARS-CoV-2 in accordance with the WHO guidelines. The kits used are listed in Supplementary Table 2.
The discharge criteria of the recovered patients included the following: a normal body temperature for more than 3 days, obviously improved respiratory symptoms, pulmonary imaging showing obvious absorption of inflammation, and two consecutive negative SARS-CoV-2 PCR tests taken at least 24 h apart. Those who met the above criteria could be discharged. After hospital discharge, the patients continued to be in isolation for 14 days at a rehabilitation center, with health monitoring. They wore a mask and lived in a private room with good ventilation. Although the patients had contacts with the staff at the rehabilitation center, the contact was limited, and the staff wore personal protective equipment (including medical protective clothing, medical protective masks, protective goggles, medical latex gloves, shoes protectors, and work caps). The patients were followed up via regular hospital visits every 2 weeks. The patients were tested again 1 month after hospital discharge, with retests every month thereafter. Testing was organized by the local community. If the patient was positive again, he/she was transferred to the hospital or the isolation center. The patient was tested again on the 3rd–5th day after transfer and on the 11th–13th day. Individuals who had close contact with the patient were quarantined in the isolation center and were tested on the 1st–2nd day after entering quarantine and again on the 10th–14th day. Close contacts were defined as individuals living in the same houses as the patients.
RT-PCR test
Nasopharyngeal swab
The sampler gently holds the person’s head with one hand, with the swab in the other, and slowly inserts the swab via the nostril so that it is deep, along the bottom of the lower nasal canal. Because the nasal canal is curved, the swab should not be forced so as to avoid traumatic bleeding. When the tip of the swab reaches the posterior wall of the nasopharyngeal cavity, it is gently rotated once (pause for a moment in case of reflex cough). It is then slowly removed, and the swab tip is dipped into a tube containing 2–3 ml of virus preservation solution (isotonic saline solution, tissue culture solution, or phosphate buffer). The swab stem is then discarded and the tube cap is tightened.
Pharynx swab
The sampled person first gargles with normal saline. The sampler then immerses the swabs in sterile saline (virus preservation solution is not allowed so as to avoid antibiotic allergies) and holds the person’s head up slightly. With one’s mouth wide open, making a sound “ah” to expose the lateral pharyngeal tonsils, the sampler inserts the swabs, wipes it across the tongue roots, and wipes both sides of the pharyngeal tonsils with pressure at least three times. The sampler then wipes on the upper and lower walls of the pharynxes for at least three times and dips the swab in a tube containing 2–3 ml of storage solution (isotonic saline solution, tissue culture solution, or phosphate buffer solution). The swab is then discarded the tube cap is tightened. The pharyngeal swabs can also be placed in the same tube together with the nasopharyngeal swab.
SARS-CoV-2 nucleic acid assay (real-time fluorescence-based RT-PCR assay)
The primers and probes used targeted the ORF1ab and N gene regions of SARS-CoV-2. Kit instructions of the manufacturers were followed for nucleic acid extraction, the real-time fluorescence-based RT-PCR reaction system, and the reaction conditions.
Result assessment
Negative: no Ct value or Ct value≥ 40. Positive: Ct value < 37. Gray zone: Ct value between 37 and 40; in these cases, a repeat test was recommended. If the Ct value was < 40 and the amplification curve had obvious peaks, the sample was considered to be positive; otherwise, it was considered to be negative. When a commercial kit was used, the instructions provided by the manufacturer prevailed.
Statistical analysis
In this study, categorical variables are presented as numbers and percentages, and continuous variables are presented as the median (interquartile range, IQR). Student’s t-test was used to compare the continuous variables of two groups. The multivariable and univariable logistic regression model was used to determine the associated factors. All statistical analyses were performed using R version 3.4.11 (www.r-project.org). A P value less than 0.05 was considered to indicate statistical significance.