key: cord-253245-433mg0ke
authors: Gao, Zhiru; Xu, Yinghui; Guo, Ye; Xu, Dongsheng; Zhang, Li; Wang, Xu; Sun, Chao; Qiu, Shi; Ma, Kewei
title: A systematic review of re-detectable positive virus nucleic acid among COVID-19 patients in recovery phase
date: 2020-08-05
journal: Infect Genet Evol
DOI: 10.1016/j.meegid.2020.104494
sha: 
doc_id: 253245
cord_uid: 433mg0ke

A large number of coronavirus disease 2019 (COVID-19) patients have been cured and discharged due to timely and effective treatments. While some discharged patients have been found re-positive nucleic acid again in the recovery phase. Until now, there is still a great challenge to its infectivity and the specific potential mechanism which need further discussion. However, more intensive attention should be paid to the prognosis of the recovered patients. In this review, we mainly focus on the characteristics, potential reasons, infectivity, and outcomes of re-detectable positive patients, thereby providing some novel insights into the cognition of COVID-19.

remarkable progress, enabling a great number of patients to be cured and discharged.

The criteria for discharge in China are listed as follows: 1) Temperature returned to normal for longer than 3 consecutive days; 2) Respiratory symptoms resolved significantly; 3) Improvement of acute exudative lesions of chest computed tomography (CT); 4) Two consecutive respiratory specimens tested negative for reverse transcriptase-polymerase chain reaction (RT-PCR) tests (sampling interval of at least 24 h)

[http://www.nhc.gov.cn/yzygj/s7653p/202003/46c9294a7dfe4cef80dc7f5912eb1989.s html]. A recent study reported that four medical workers aged 30-36 years who had re-detectable positive (RP) for SARS-CoV-2 within 5-13 days after being cured and discharged, indicating that some of the recovered patients may still be virus carriers, which caused widespread concern (Lan et al., 2020). However, there is currently insufficient knowledge about the characteristics of RP patients. In the manuscript, we reviewed characteristics, potential reasons, infectivity, treatment, and outcome of RP patients in order to explain this phenomenon.

According to several reports, some patients were found to be re-positive RT-PCR results of virus nucleic acid after 5-13 days of medicine discharge to re-positive RT-PCR results . The finding indicated that the RP patients accounted for 14.5% (38/262) of discharged patients during the same follow-up period. They were characterized as young (mostly under 14 years old), asymptomatic or minor clinical symptoms, and no disease progression after re-admission (An JH, et al., 2020) . A follow-up case of 20 discharged COVID-19 be required for them (Fu et al., 2020) .

Many studies have shown that RT-PCR results of most RP patients, which may not be considered as simple viral relapse or secondary infection (Xiao et al., 2020) . The underlying mechanism of RP patients remains elusive, the specific reasons need to be further explored. Some experts speculated that the potential reasons might be related to some factors such as virology, detection of specimens or patients' condition.

For virology of SARS-CoV-2, it may be related to the biological characteristics of the virus. Viral residue, intermittent viral release, and periodic changes of virus replication are generally considered as the main factors (An JH, et al., 2020; .

A pathological examination of a patient who reached the discharge standard but died of sudden cardiac arrest found that SARS-CoV-2 virus still remained in the lung cells and caused lung pathological changes. Although the results of the three nucleic acid tests were negative for the patient, there were viral residue in the lungs, so even if the patient was discharged, we supposed that virus would transfer positive again after a period of time (Yao et al., 2020) . In addition, it may be linked to the diversity of SARS-CoV-2 genomic and the characteristics of repeated mutations (van Dorp et al., 2020) . In other words, we lack a comprehensive understanding of SARS-CoV-2, which may be continuously or repeatedly positive during the course of the disease (Chen et al., 2020).

For detection of specimens, it may be related to the collection methods, processing procedures, and detection methods (Chen et al., 2020). Differences of sample types, improper nucleic acid extraction, insufficient viral level or inappropriate sample pretreatments will lead to false-negative detection results by PCR method in a certain rate (Pan et al., 2020; Xie et al., 2020; Zou et al., 2020) . This may cause COVID-19

patients whose virus has not been completely clearance to reach the current discharge criteria. Then after discharge, the virus will continue to replicate in a lower level, making this part of patients re-detected positive again once viral loads rise to the detection level. Meanwhile, the virus mainly concentrates in the lower respiratory J o u r n a l P r e -p r o o f Journal Pre-proof tract and the lung, so false-negative tests may appear when collecting throat swabs (Zhou et al., 2020) . In addition, initial studies reported that the SARS-CoV-2 RNA could be detected in the feces of 81.8% recovered patients (54/66), even in those with negative throat swabs (Ling et al., 2020) . And later studies revealed that the viral RNA can persist in fecal samples for nearly 5 weeks after the patients' respiratory specimens detected negative (Wu et al., 2020b) . Other studies have also demonstrated the importance of rectal swab-testing, which should be taken into consideration (Wolfel et al., 2020; Xu et al., 2020) . Due to the possible presence of SARS-CoV-2 in the digestive tract, the current methods of discharge criteria for oral/nasopharyngeal swab virus detection are not accurate (Liu et al., 2020a) .

Therefore, using more sensitive detection method and collecting different samples to test will be a more effective way to overcome false-negative detection .

For patients' condition, it may be related to the underlying diseases, degree of infection, and treatment methods, among which hypertension and diabetes are the most common underlying diseases (Liu et al., 2020b) . Once infected with SARS-CoV-2, the underlying diseases will be more difficult to control, leading to more complications and dysfunction of more organs and immune system (Hussain et al., 2020). Ultimately, the hospital stay will be prolonged, and patients are more likely to relapse or infection after discharge due to their lower immune function. Also, some studies have indicated that the use of antiviral drugs may affect the host's cellular immunity. Although virus can be cleared by antiviral drugs in the initial phase, patients' immune function decreased. Once antiviral therapy discontinued, virus will tend to be activated due to lack of normal cellular immunity, which may be regarded as one of the reasons for recurrence of SARS-CoV-2, but it still needs more evidence to verify that (Balachandar et al., 2020; Wu et al., 2020) .

Theoretically, the infectivity of patients is determined by the existence of the virus in different body fluids, secretions, and excreta (Ling et al., 2020) . And the viral infectivity J o u r n a l P r e -p r o o f Journal Pre-proof mainly depends on its reproduction state (Wölfel et al., 2020) . In a study from South Korean, no active virus was discovered in samples from RP patients (Kang, 2020) .

This means that re-positive virus nucleic acid does not indicate infectivity. This also can explain that although SARS-CoV-2 RNA can be detected in RP patients, no cases of infection have been reported so far. For example, all close contacts of RP patients were tested negative for nucleic acid and showed no suspicious clinical symptoms An {JH, et al., 2020) . Another case report showed that there was no significant change in chest CT of RP patients and no family members were infected, which suggested that RP patients have no or lower infectivity (Lan et al., 2020) . However, the infectivity of RP patients is still needed to be verified by more studies and more cases.

Furthermore, it is important and necessary to continue epidemiological follow-up on RP patients in order to monitor their health status and explain their infectivity.

According to recent researches, RP patients usually completed negative-conversion again 2-3 weeks later, and they could heal themselves without any antibiotics or antiviral drugs, which might be related to the body's recovery immunity (An JH, et al., 2020) . In other words, even if sometimes the virus nucleic acid tested by RT-PCR is positive in the recovery phase of COVID-19, it will not cause a more serious condition, and antiviral therapy may not be required in most patients.

RT-PCR results will turn negative again within a few days as immunity function recovered . For these cases, observational therapy can be used instead of antiviral drug therapy for asymptomatic RP patients.

A recent study showed that the recovered patients acquired relatively stable and sustained immunity after being infected with SARS-CoV-2. All the subjects produced CD4 + T cell responses to the spike protein on the surface of the SARS-CoV-2, which also provided theoretical support for the vaccine under development (Grifoni et al., 2020) . The detectable and sustained high levels of IgM indicate that the acute phase of SARS-CoV-2 infection, but IgG suggests that the body has enough immune protection against the SARS-CoV-2 and IgG can persist a very long time (Xiao et al., J o u r n a l P r e -p r o o f Journal Pre-proof 2020). It has been reported that the results of IgM were negative but IgG were positive when three patients were discharged from the hospital. And these results were still the same when they were re-admitted to the hospital as virus nucleic acid transferred positive again (Fu et al., 2020) . Therefore, detection of virus nucleic acid combined with antibody is useful for determining disease status, treatment and outcome.

It has been nearly half a year since the COVID-19 epidemic spread around the world. Although a lot of patients from different countries have gradually recovered, it is very important to follow up with the patients who recovered from the infection. There are still some unknowns in the face of recovered patients. In this situation, it is necessary to understand the characteristics of RP patients and determine if they are potential threats to the public. Moreover, RP patients should be paid more attention and it is important for early control of this epidemic in the whole world.

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