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\begin{document}

\title{Risk factors associated with PCR repositivity in patients with COVID-19
after recovery in Guangzhou, China: a retrospective cohort study}



\author[1]{Lei Luo}%
\author[2]{Dan Liu}%
\author[1]{Zhoubin Zhang}%
\author[2]{Zhihao Li}%
\author[1]{Chaohui Xie}%
\author[2]{Zhenghe Wang}%
\author[1]{Zongqiu Chen}%
\author[2]{Peidong Zhang}%
\author[2]{Xiru Zhang}%
\author[2]{Yujie Zhang}%
\author[2]{Wenfang Zhong}%
\author[2]{Wenting Zhang}%
\author[2]{Pei Yang}%
\author[2]{Qingmei Huang}%
\author[2]{Weiqi Song}%
\author[2]{Hui Wang}%
\author[2]{Chen Mao}%
\affil[1]{Guangzhou Center for Disease Control and Prevention}%
\affil[2]{Southern Medical University}%


\vspace{-1em}



  
  \date{May 26, 2024}


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\selectlanguage{english}
\begin{abstract}
Some patients retested positive for SARS-CoV-2 following negative
testing results and discharge. However, the potential risk factors
associated with redetectable positive test results in a large sample of
patients who recovered from COVID-19 have not been well estimated. A
total of 745 discharged COVID-19 patients were enrolled between January
30, 2020, and September 9, 2020, in Guangzhou, China. Data on the
clinical characteristics, comorbidities, drug therapy, RT-PCR testing,
and contact modes to close contacts were collected. Patients who tested
positive for SARS-CoV-2 after discharge (positive retest patients) were
confirmed by guidelines issued by China. The repositive rate in
different settings was calculated. Among 745 discharged patients, 157
(21.1\%; 95\% CI, 18.2\% to 24.0\%) retested positive, of which 55
(35.0\%) were asymptomatic, 15 (9.6\%) had mild symptoms, 83 (52.9\%)
had moderate symptoms and 4 (2.6\%) had severe symptoms at the first
admission. The median time from discharge to repositivity was 8.0 days
(IQR, 8.0 to 14.0 days). Most positive retest patients were without
clinical symptoms, and lymphocyte cell counts were higher than before
being discharged. The likelihood of repositive testing for SARS-CoV-2
RNA was significantly higher among patients who were younger age (OR,
3.88; 95\% CI, 1.74 to 8.66, 0 to 17 years old), had asymptomatic
severity (OR, 4.36; 95\% CI, 1.47 to 12.95) and did not have clinical
symptoms (OR, 1.89; 95\% CI, 1.32 to 2.70, without fever). We found that
the positive retest rate of COVID-19 was relatively high, and these
patients tested positive again with a median of 8.0 to 14.0 days after
discharge. Positive retest results were mainly observed in young
patients without severe clinical symptoms. These findings suggest that a
significant proportion of patients could carry viral fragments for a
long time, and effective management, such as a prolonged quarantine
phase for discharged patients, is necessary.%
\end{abstract}%



\sloppy


\textbf{Introduction}

Since the outbreak in December 2019, coronavirus disease 2019
(COVID-19), caused by severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2), has given rise to a worldwide pandemic(Li et al., 2020).
As of December 13, 2020, 70 million COVID-19 cases and 1.6 million
deaths have been reported globally(WHO, 2020). At the same time, tens of
millions of patients with COVID-19 have recovered and been discharged
from the hospital. However, some patients affected by COVID-19 who fully
met the criteria for discontinuation of quarantine had another positive
real-time reverse transcriptase-polymerase chain reaction (RT-PCR)
result at a follow-up visit(An et al., 2020; F. Hu et al., 2020; Lan et
al., 2020; Mei et al., 2020; Su et al., 2020; Zheng et al., 2020), which
increases the complexity of disease control and has attracted widespread
concern.

Several studies, mainly case reports, have been performed to investigate
the clinical characteristics and virologic course of discharged
patients(An et al., 2020; F. Hu et al., 2020; Lan et al., 2020; Mei et
al., 2020; Su et al., 2020; Zheng et al., 2020). However, to date, many
questions about patients who tested positive for SARS-CoV-2 again
(hereafter, positive retest patients) have not been answered; these
questions include the overall prognosis of patients with COVID-19 after
meeting the criteria for hospital discharge, the potential risk factors
associated with redetectable positive test results, and whether the
persistent presence of virus fragments means that the discharged patient
is still contagious. As the number of discharged patients increases,
effective management becomes critical to successfully reducing the
spread of SARS-CoV-2. To promote the comprehensive rehabilitation of
COVID-19 patients, China has implemented a series of measures for
discharged COVID-19 patients, including management of quarantine,
regular follow-up, health monitoring, and rehabilitation therapy, which
provide empirical information and evidence support for the management of
patients with COVID-19(National\_Health\_Commission\_of\_China, 2020).

In this retrospective cohort study, we examined the potential risk
factors associated with redetectable positive test results among 745
patients affected by COVID-19 after meeting the criteria for hospital
discharge in Guangzhou, China.

\textbf{Material and methods}

\textbf{Patients and study design}

Only COVID-19 patients who met all the following
criteria(National\_Health\_Commission\_of\_China, 2020 ) could be
discharged from the hospital and admitted to the follow-up study
project: (1) body temperature returned to normal for more than 3
consecutive days, (2) had significant improvement in any symptom, such
as fever, dry cough and expectoration, (3) had substantial improvement
in acute exudative lesions on chest computed tomography (CT) images, and
(4) had negative RT-PCR test results for SARS-CoV-2 RNA from a
nasopharyngeal swab, an anal swab or other respiratory specimens two
consecutive times (at least 24 hours apart).

Between January 30, 2020, and September 9, 2020, a total of 745 patients
who officially recovered from COVID-19 were discharged from the hospital
and enrolled in this study in Guangzhou, China. All discharged patients
were required to undergo 14 days of quarantine in designated health care
facilities and 28 days of community follow-up to observe their clinical
symptoms and RT-PCR results. The positive retest patients were
re-admitted to the hospital for therapy, and close contacts were traced
and followed-up. The remaining discharged patients who continued to have
negative RT-PCR test results were closely followed-up in their
communities. \textbf{Fig. 1} shows the flowchart of the management of
discharged patients.

This study was reviewed and approved by the Ethics Committee of the
Guangzhou CDC (GZCDC). As required by the National Health Commission of
China, CDCs were responsible for the work for an ongoing public health
response to COVID-19, and our cohort study was based on the data from
the GZCDC. Patients were informed about the surveillance before
providing written consent, and data were collected and anonymized for
analysis. All analyses of personally identifiable data took place onsite
at the GZCDC.

\textbf{Definition and Confirmation of Positive Retest Patients}

This study refers to discharged patients who tested positive for
SARS-CoV-2 again using RT-PCR as positive retest patients. Based on open
reading frame 1ab (ORF 1ab) and nucleocapsid (N) protein genes in the
SARS-CoV-2 genome, RT-PCR was performed to assess the results(Corman et
al., 2020; Luo, Liu, Zhang, et al., 2020). If the cycle threshold (Ct)
value of RT-PCR is less than 37, the sample is positive; if the Ct value
ranges between 37 and 40, and if the amplification curve has an obvious
peak, then the sample is considered positive. Otherwise, the sample is
considered as negative.

The following three conditions are considered positive. First, the two
targets, ORF 1ab and N protein, are both positive. Second, in case of
the result showing positivity for one target, samples shall be
recollected for another test. If it is still positive for a single
target, the result should be considered positive. Third, if two types of
specimens show one single target as positive at the same time or if one
target is positive in two samples of the same type, then the result
should be considered positive.

\textbf{Measures}

Quarantine for discharged patients

After discharge from the hospital, patients were put under centralized
quarantine and health monitoring for 14 days at designated health care
facilities. During the quarantine period, the discharged patients lived
in a well-ventilated single room, dined separately, practiced hand
hygiene, and minimized close contacts. Nasopharyngeal and anal specimens
collected on the 1\textsuperscript{st}, 7\textsuperscript{th}, and
14\textsuperscript{th}days or more frequently were sent to the
laboratory for RT-PCR testing. The discharged patients were monitored
for body temperature, and medical staff recorded whether they had
respiratory symptoms (such as fever and dry cough) or digestive tract
symptoms (such as diarrhea) every day. If the RT-PCR test result was
consecutively negative and no symptoms or CT images progressed, these
patients could return to normal life and be regularly followed up by the
community after the discontinuation of quarantine. If they were
symptomatic (had clinical manifestations and had a positive RT-PCR test
result) or asymptomatic (had no clinical manifestations but had a
positive RT-PCR test result) patients, diagnosis and treatment should be
conducted strictly in accordance with Chinese clinical guidance for
COVID-19(National\_Health\_Commission\_of\_China, 2020 ). When the
positive retest patients met the hospital discharge criteria, they were
quarantined for another 14 days.

Follow-up for discharged patients

After discharged patients completed 14 days of quarantine, it is
recommended for these patients to be followed up in their communities
for at least 28 days. GZCDC follows the health management plan for
discharged COVID-19 patients released by the National Health Commission
of China(National\_Health\_Commission\_of\_China, 2020), and RT-PCR
testing was performed on the 14\textsuperscript{th} and
28\textsuperscript{th} days after quarantine or more frequently. During
the follow-up period, if a person tested positive by RT-PCR, he or she
should go to the hospital for a comprehensive evaluation as soon as
possible, and treatment should be conducted according to the latest
national clinical guidance. If a person tested negative by RT-PCR but CT
images showed abnormalities or symptoms occurred, symptomatic treatment
could be given according to the related disease(s).

Close contact tracing and management

If the discharged patient was diagnosed as a positive retest patient,
close contacts should be traced and followed up. Close contacts are to
be put under centralized quarantine and medical observation. If this is
not feasible, home quarantine and health monitoring can be used instead.
At home, they were recommended to wear a mask, live in a well-ventilated
single room, reduce close contact with family members, wash hands
frequently and avoid going out(Chinese\_CDC, 2020). The quarantine
period should last until 14 days after the last contact without
effective protection with a positive retest patient. Samples including
nasopharyngeal and anal swabs were all collected for RT-PCR diagnosis in
an attempt to reduce the chance of false negatives caused by differences
in primer specificity and sensitivity. Monitoring and evaluating close
contacts were documented in a previous study(Luo, Liu, Liao, et al.,
2020).

\textbf{Data collection}

The information collected for COVID-19 patients included demographic
characteristics (age, sex and continent), comorbidities (hypertension,
diabetes, etc.), drug therapy, severity, clinical symptoms (fever, dry
cough, expectoration, myalgia, diarrhea, shortness of breath, fatigue,
etc.), radiological examinations (CT), and blood examinations (white
blood cell count, lymphocyte cell count and lymphocyte cell percentage)
at the first admission. The second admission information of positive
retest patients was also collected. The information collected for close
contacts included demographic characteristics, quarantine site (health
care facilities and home), frequency of contact (often, moderate, and
occasional), and contact modes (household, public transportation, health
care settings, workplaces, and entertainment places).

\textbf{Statistical analysis}

The repositive rate of SARS-CoV-2 was estimated by dividing the number
of positive retest patients by the number of COVID-19 patients.
Categorical variables are described as absolute numbers and percentages
(\%). Skewed and normally distributed continuous variables are described
as the median (interquartile range {[}IQR{]} or range) and mean
(standard deviation {[}SD{]}), respectively. Chi-square tests and
t-tests were used to compare characteristics between positive retest
patients and negative retest patients.

Univariate and multivariable logistic regression models(Tripepi, Jager,
Dekker, \& Zoccali, 2008) were performed to estimate odds ratios (ORs)
and 95\% confidence intervals (95\% CIs) for associations of potential
risk factors with retested positivity. Age (0-17, 18-44, 45-59, or [?]60
years), sex (male or female), continent (Asia, Africa or others),
severity (asymptomatic, mild, moderate, or severe) and clinical symptoms
(fever, dry cough, expectoration, myalgia, diarrhea or shortness of
breath) at the first admission were included in the multivariable model.

Analyses were all performed with SAS software (version 9.4 for Windows,
SAS Institute, Inc., Cary, NC, USA). Statistical tests were two-sided,
and \emph{P} values of less than 0.05 were considered to indicate
statistical significance.

\textbf{Results}

\textbf{Clinical characteristics of 745 patients with COVID-19}

A total of 745 patients who officially recovered from COVID-19 were
enrolled in this study, and they were all tested for SARS-CoV-2 by
RT-PCR after discharge. Up to September 21, 2020, 157 patients (21.1\%;
95\% CI, 18.2 to 24.0) retested positive by RT-PCR and were transferred
to the designated hospital. \textbf{Fig. S1} shows the distribution of
COVID-19 patients by date of the first admission, and the
characteristics at the first admission of the 157 positive retest
patients are shown in \textbf{Table 1} . Positive retest results were
observed in patients in all age groups (age ranging from 3 months to
82.0 years, with a median age of 33.0 years), which was significantly
younger than that of negative retest patients (median age of 38.0
years). The days from the first admission to discharge of positive
retest patients were significantly shorter than those of negative retest
patients (11.2 {[}5.5, 16.4{]} vs. 13.0 {[}8.0, 20.0{]} days). During
their first admission, all patients were updated by the progression of
their illness, and the most severe condition was their final severity
designation. One in three positive retest patients was asymptomatic
compared with one in six negative retest patients (\emph{P}
\textless{}0.001). The positive retest patients had fewer comorbidities
(such as cardiovascular disease, 1 {[}0.6\%{]} vs. 29 {[}4.9\%{]}), were
less likely to be treated with anti-infective drugs (58 {[}36.9\%{]} vs.
308 {[}52.4\%{]}) and were likely to be in the ICU (4 {[}2.6\%{]} vs. 37
{[}6.3\%{]}). After discharge from the hospital, RT-PCR testing was
performed regularly, and the median number of tests was 4.0 times (IQR,
3.0 to 6.0 times) for positive retest patients, which was significantly
greater than that of negative retest patients (\emph{P}
\textless{}0.001). The median time for discharged patients retested as
being viral RNA-positive was 8.0 days (IQR, 8.0 to 14.0 days) after
discharge (\textbf{Table 1 and Fig. 2} ). After discharge, 4 (2.6\%)
patients had symptoms of dry cough, 10 (6.4\%) patients had
expectoration, 2 (1.3\%) patients had sore throat and 2 (1.3\%) had
fatigue, which was lower than that of the first admission. Among the 127
patients who underwent CT examination, 104 (81.3\%) patients had
abnormal but obvious absorption. Lymphocyte cell counts and lymphocyte
cell percentages were increased compared with those before
(\textbf{Table 2} ).

\textbf{Risk factors associated with repositivity among COVID-19
patients}

\textbf{Table 3} presents the association between various potential risk
factors and repositivity among COVID-19 patients before and after
adjustment. A higher repositivity rate of males than females (23.4\%
{[}95\% CI, 19.3 to 27.4{]} vs 18.1\% {[}13.9 to 22.3{]}) was observed,
but this difference was not statistically significant. The repositivity
rate decreased with age, with 42.9\% (27.9 to 57.8) for 0-17 years,
22.0\% (18.1 to 25.9) for 18-44 years, 16.3\% (10.7 to 21.9) for 45-59
years and 16.2\% (9.1 to 23.2) for 60 or over years (\emph{P} for trend
= 0.0023), and decreased with severity, with 34.6\% (27.2 to 42.0) for
asymptomatic, 18.5\% (10.1 to 27.0) for mild symptoms, 17.7\% (14.3 to
21.2) for moderate symptoms and 10.8\% (0.8 to 20.8) for severe symptoms
(\emph{P} for trend \textless{} 0.001). Manifestation of some symptoms
at the first admission, such as fever (26.7\% {[}22.1 to 31.4{]} vs
16.2\% {[}12.6 to 19.8{]}), was associated with an increased risk of
repositivity. In addition, comorbidities, CT lung abnormalities, and
some clinical symptoms (such as fatigue, chills, and sore throat) were
not separately assessed due to multicollinearity with age, severity and
other clinical symptoms, and the repositivity rate of COVID-19 by these
variables is shown in \textbf{Table S1} .

\textbf{Management and infection of close contacts}

Because all the discharged patients were put under centralized
quarantine for 14 days at health care facilities, only 26 positive
retest patients had close contacts, and 148 close contacts were
traced.\textbf{Table 4} presents the characteristics of positive retest
patients and close contacts. The demographic characteristics of the 148
close contacts were as follows: sex distribution was more male (89,
60.1\%) than female (59, 39.9\%); all age groups were included, and 18
to 44 years old accounted for most of the close contact (92, 62.2\%). A
total of 137 (92.6\%) close contacts were quarantined at health care
facilities, and 11 (7.4\%) close contacts quarantined at home. Among all
close contacts, 41.2\% (61/148) were public transportation contacts,
28.4\% (42/148) were household contacts, 21.0\% (31/148) were
entertainment place contacts, 8.1\% (12/148) were workplace contacts and
1.4\% (2/148) were healthcare setting contacts. Positive retest patients
with moderate severity had the closest contacts (96, 64.9\%), followed
by asymptomatic patients (40, 27.0\%). After quarantine for 12.0 days
(IQR, 6.0 to 14.0 days) at a health care facility or at home and 4.5
times (IQR, 3.0 to 10.0 times) of RT-PCR testing, 148 close contacts
tested negative for SARS-CoV-2 RNA, and no suspicious clinical symptoms
were reported.

\textbf{Discussion}

We found that the repositive rate of SARS-CoV-2 was over 20\% (157/745,
21.1\%) among discharged patients affected by COVID-19 at a follow-up
visit after at least 6 weeks. They reported positive RT-PCR testing
results with median days 8.0 to 14.0 after discharge. Over 4 in 10
children and adolescents were found to be positive again; in contrast,
the repositivity rate of SARS-CoV-2 in middle-aged and elderly
individuals was 16\%. Moreover, patients with more clinically severe
disease were less likely to have redetectable positive test results than
those with mild severity; asymptomatic patients were most likely to have
redetectable positive test results. Manifestation of certain symptoms at
first admission, such as fever, was also associated with a lower risk
for repositivity. Based on the Chinese guidelines for discharged
patients (National\_Health\_Commission\_of\_China, 2020), positive
retest patients were required to quarantine for a second time. No other
positive patients emerged within their families and close contacts.

Several studies, mainly case reports, have been performed to investigate
the percentage of retested positivity and the clinical characteristics
of discharged patients(Habibzadeh et al., 2020; Lan et al., 2020; Tao et
al., 2020). Previous studies reported that the repositivity rate ranged
from 6.9\% to 69.0\% for discharged patients(Habibzadeh et al., 2020;
Landi et al., 2020; Tao et al., 2020). However, the studies were limited
to a small number of patients with mild or moderate infection. In our
study, we evaluated the overall prognosis of patients with COVID-19
after meeting the criteria for discharge in Guangzhou, China. After
screening 745 discharged patients, up to September 21, 2020, the
repositivity rate was over 20\% (157/745), which was higher than that in
other cities of China (20/182, 11.0\%)(Yuan et al., 2020) and Italy
(16.7\%)(Landi et al., 2020), and this may be due to the longer
follow-up time, more stringent monitoring and higher frequency of RT-PCR
testing in Guangzhou. Our study has lasted more than 7 months since the
start of the outbreak, which was far longer than other study (most
lasted for one or two months)(Lu et al., 2020; Tao et al., 2020; Yuan et
al., 2020; Zheng et al., 2020) and to some extent represented the
overall prognosis of the disease.

According to the Chinese clinical guidance for
COVID-19(National\_Health\_Commission\_of\_China, 2020 ), all positive
retest patients should test negative for nasopharyngeal and anal swabs
for two successive tests before discharge. Then, all discharged patients
were continuously quarantined in designated health care facilities with
strict interventions on disease transmission. Thus, the identification
of another positive SARS-CoV-2 test during the quarantine period likely
excludes the possibility that positive retest patients are caused by
secondary viral infection. A recent study also experimentally confirmed
that the virus was involved in the initial infection instead of a
secondary infection(F. Hu et al., 2020). Abnormal CT and lymphopenia are
common and correlate with poor clinical outcomes in patients with
COVID-19(Cheng et al., 2020). Most positive retest patients at the
second admission showed increased lymphocyte cell counts, and CT
examination showed abnormal but obvious improvements (\textbf{Table 2}
), suggesting that positive retest patients have no obvious disease
progression but are still asymptomatic carriers of the virus.

Our results showed that the observation of positive retest patients was
not random and was mainly observed in young patients without severe
clinical symptoms, which was consistent with previous studies(F. Hu et
al., 2020; Lu et al., 2020). At present, it has been reported that
negative conversion of viral RNA generally takes 2 to 3 weeks or
longer(X. Hu et al., 2020; Hung et al., 2020; To et al., 2020; L. Zou et
al., 2020), and one study showed that SARS-CoV-2 nucleic acid existed in
fecal samples for 47 days after the first symptom onset(Wu et al.,
2020). In our study, the days of first hospitalization were shorter in
positive retest patients than in negative retest patients (\textbf{Table
1} ), suggesting that the SARS-CoV-2 virus may not be completely
eliminated due to the lighter symptoms and the faster attainment of the
discharge standard. In addition, one study reported that recurrently
positive RT-PCR testing results in patients with three consecutive
negative results were significantly decreased compared with those in
patients with two consecutive negative results(Y. Zou et al., 2020),
suggesting that a prolonged quarantine phase is necessary.

Among positive retest patients in our study, no families or close
contacts of positive retest patients tested positive, which was
consistent with current studies(Chandrashekar et al., 2020; Lu et al.,
2020). All positive retest patients had observed social distancing
measures and worn face masks. Regarding these observations, it is very
difficult to affirm whether these patients were truly contagious. RT-PCR
testing does not discriminate between an infectious virus and
noninfectious RNA(Atkinson \& Petersen, 2020; Quick et al., 2017).
Therefore, positive testing may not necessarily imply an active
infection or ability to transmit infection. However, whether discharged
patients have infectivity is an issue of concern around the world at
present. One recent study reported that no infectious strain could be
obtained by culture, and no full-length viral genomes could be sequenced
using samples of positive retest patients(Lu et al., 2020). However,
other studies found that active SARS-CoV-2 viral replication was
observed(Gousseff et al., 2020) and managed to obtain a nearly
full-length viral genome sequence in positive retest patients by
detecting intracellular SARS-CoV-2 subgenomic messenger RNA (sgmRNA)(F.
Hu et al., 2020), and the presence of SARS-CoV-2 sgmRNA was widely
accepted as direct evidence of active viral replication and
production(Kim et al., 2020; W\selectlanguage{ngerman}ölfel et al., 2020). Furthermore, a recent
study found that SARS-CoV-2 viral particles remained in the lungs of
patients in the hospital whose nasopharyngeal swab sample testing
results were negative at three consecutive times(Yao et al., 2020).
Therefore, careful consideration should be given to the potential for
patients who are positive retest patients to become chronic virus
carriers.

Our study has some limitations. First, as our data were based on the
public health response to COVID-19, sample collection did not follow a
stringent study design. Therefore, some of the patients, especially in
the early stage, had missing fecal samples. Second, nasopharyngeal swab
samples cannot differentiate whether the virus comes from the
nasopharynx or from secretions from the lower respiratory tract; thus,
virus elimination in the lower respiratory tract cannot be confirmed. In
contrast, the positive rate of RT\selectlanguage{english}-PCR testing through alveolar lavage
fluid may be higher. However, this method is invasive and cannot be
widely performed in clinical practice. In our opinion, both qualities of
respiratory samples and the variability of technique sensitivity can be
attributed to the influencing factors of repositivity. Third, as the
discharge patients were usually placed under centralized quarantine and
medical observation, the infectivity of the positive retest patients
might be underestimated.

In summary, we found that the repositivity rate of discharged patients
was relatively high (21.1\%), and they tested positive with a median of
8.0 to 14.0 days after discharge. The observation of positive retest
patients was not random and was mainly observed in young patients
without severe clinical symptoms. We suspected that SARS-CoV-2 may not
be completely eliminated in positive retest patients due to the lighter
symptoms and the faster attainment of the discharge standard. Meanwhile,
as the discharge patients were usually put under centralized quarantine,
it is difficult to affirm whether these patients were truly contagious.
These findings suggest that a significant proportion of patients could
carry viral fragments for a long time, and effective management, such as
a prolonged quarantine phase for discharged patients, is necessary.

\textbf{Acknowledgements.} We acknowledge all staffs involved in the
prevention and control of COVID-19 at the Guangzhou Centers for Disease
Control and Prevention. We thank all patients involved in the study.

\textbf{Conflicts of interest.}All authors report no potential
conflicts.

\textbf{Author Contribution.} D.L. contributed to the statistical
analyses and drafted the manuscript. C.M., L.L., D.L., Z.H.L., Z.H.W.,
P.D.Z, X.R.Z., Y.J.Z., W.F.Z. and W.Q.S. revised the final manuscript.
Z.B.Z., C.J.X., Z.Q.C., W.T.Z., P.Y. and Q.M.H. collected the
epidemiological and clinical data. H.W. and D.L. are responsible for
summarizing all epidemiological and clinical data, and contributed to
the data cleaning. All authors critically reviewed the manuscript for
important intellectual content.

\textbf{Data Availability Statement.} The data that support the findings
of this study are available from the corresponding author upon
reasonable request.

\textbf{Financial support.} This work was supported by the Guangdong
Province Higher Vocational Colleges and Schools Pearl River Scholar
Funded Scheme (2019), the Construction of High-level University of
Guangdong (G820332010, G618339167 and G618339164), Young Elite
Scientists Sponsorship Program by CAST (2019QNRC001), the National
Natural Science Foundation of China (82041030), the Zhejiang University
special scientific research fund for COVID-19 prevention and control
(K920330111).

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\par\null

\textbf{Figures legend:}

\textbf{Fig. 1.} Study flow diagram.

\textbf{Fig. 2.} Distribution of days from discharge to re-positivity
among re-positive cases according to the severity at first
hospitalization.

\textbf{Tables:}

\textbf{Table 1.} Characteristic of 157 re-positive and 588
non-re-positive cases with COVID-19.

\textbf{Table 2.} Characteristic of 157 re-positive cases at first and
second admission.

\textbf{Table 3.} Risk factors associated with re-positivity among
COVID-19 cases (n=745).

\textbf{Table 4.} Characteristic of re-positive cases and the close
contacts.

\textbf{Table S1.} Prevalence rate of Re-positivity among 745 COVID-19
cases.

\textbf{Fig. S1.} Distribution of date of first admission in cases with
and without re-positivity.

\textbf{Hosted file}

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