key: cord-0959609-cjs8ao1s authors: Raveendran, A.V. title: COVID-19 re-infection: Diagnostic challenges and proposed diagnostic criteria date: 2021-02-11 journal: Diabetes Metab Syndr DOI: 10.1016/j.dsx.2021.02.007 sha: 2c330b4c254d32992d519c63bbc2aba0e522a47e doc_id: 959609 cord_uid: cjs8ao1s nan In a typical case with two separate episodes of symptoms of acute SARS-CoV-2 infection with positive RT-PCR and genetic studies showing infection with two different variants after two separate episodes of exposure to positive cases of COVID-19, with clinical recovery and RT-PCR negativity in between indicate reinfection with SARS-CoV-2. But in clinical practice, there are lots of challenges in the diagnosis of first infection with SARS-CoV-2 and COVID-19 re-infection. (Table 1 ) Based on our clinical experience and after reviewing relevant literature we are proposing criteria to diagnose COVID-19 re-infection (table 2) . Demonstrating the two episodes of infection by different strains of SARS-CoV-2 confirms the diagnosis of re-infection. Single nucleotide variation more than 10 or demonstration of two different variant by lineage, clades or phylogenetic analysis confirms that two infections are caused different virus [14, 15, 16] . Considering the possibilities of intra-host mutation (mutation occurring in the virus while inside the host body) SNV more than 10 is taken significant because, virus can undergo 2 nucleotide variations per month. The two episodes of infection if proved different by genetic clades or lineage it is a stronger indicator of re-infection [15, 16] . Two separate episodes of symptoms suggestive of acute COVID-19 also favor the diagnosis of re-infection. But there are lots of infections which can present with similar symptoms. Presence of "long COVID-19" symptoms has to be differentiated from the symptoms of acute infection. In addition to that a significant proportion of individuals infected with SARS-CoV-2 are asymptomatic. If both episodes of infections are asymptomatic, we may miss the case without laboratory screening. Two episodes of infection with SARS-CoV-2, confirmed by positive RT-PCR have the advantage of including both symptomatic and asymptomatic infections. But prolonged viral shedding is reported even up to 104 days, resulting in RT-PCR positivity months after the first positive result [8] . It has to be differentiated from re-infection. Presence of viral RNA fragments, which are non-infectious, can also cause false positive RT-PCR, which can be differentiated from re-infection by viral culture. Cycle threshold (CT) value also helps to differentiate these two. CT value is the number of cycles of PCR amplification required to detect the gene target. It is high in those with low viral load and vice versa. High CT value in persistent viral shedding helps to differentiate it from re-infection, where CT value is low. A person who is found to be positive for antibodies, without any history of vaccination if subsequently develop RT-PCR positivity or evidence of acute SARS-CoV-2 infection, it also favors the diagnosis of re-infection. But all the people who had infection will not develop antibodies and it will gradually disappear even in those who had antibodies. 33% of COVID-19 recovered patients are negative for antibodies during convalescent period (39days average) 40% at 8 weeks [17, 18] . Viral culture helps to assess infectivity and cell culture, its cytopathic effects which will help to differentiate prolonged PCR positivity due to infection from persistence of viral fragments. Demonstration of definite period of recovery in between the episode also favors re-infection. Longer the time gap between 2 episodes, higher the chance of reinfection. It can be clinical recovery (where patients will be asymptomatic before the onset of second episode) or laboratory recovery or microbiological recovery (where RT-PCR is negative). Those with "long COVID" symptoms after the first episode will not be asymptomatic during the recovery period. Differentiation of "long COVID" symptoms from symptoms of acute SARS-CoV-2 infection helps to solve this confusion. When the viral load is declining and reaching near the detection threshold level, we may get negative or positive RT-PCR report depending upon that particular sample characteristic. A negative RT-PCR between two positive RT-PCR is possible in such scenario causing confusion about reinfection. Viral culture and CT value helps to differentiate. Epidemiological criteria J o u r n a l P r e -p r o o f The one who recovered from SARS-CoV-2 infection develops symptoms of acute COVID-19 again after exposure to COVID-19 cases also favors re-infection. Persistent viral shedding can lasts up to 104 days. Even after the respiratory samples become negative, gastrointestinal shedding can continue for weeks. A long gap between first and second episode favors re-infection. With the proposed criteria, clinicians will be able to categories re-infection as confirmed, probable or possible cases, which will give uniformity in reporting and managing cases of re-infection. (Table 3) The major limitation of this criterion is that in laboratory test negative individuals, if one or both episodes are asymptomatic, we will miss the diagnosis of reinfection and it cannot be categorized based on the proposed criteria. To conclude, re-infection with SARS-CoV-2 is reported from various parts of the world. Genetic studies and viral cultures are helpful to confirm re-infection, which is not commonly available. Practicing doctors worldwide face lot of challenges in diagnosing COVID-19 re-infection. We hope that the criteria proposed will be useful for the medical fraternity all over the world. Tables Table 1 Challenges in the diagnosis of SARS-CoV-2 infection and re-infection Table 2 Proposed diagnostic criteria for COVID-19 re-infection Table 3 Interpretation of proposed diagnostic criteria for COVID-19 re-infection Reference J o u r n a l P r e -p r o o f Coronavirus protective immunity is short-lasting Lack of reinfection in rhesus macaques infected with SARS-CoV-2 Symptomatic SARS-CoV-2 reinfection by a phylogenetically distinct strain Seasonal coronavirus protective immunity is short-lasting COVID-19 re-infection by a phylogenetically distinct SARS-coronavirus-2 strain confirmed by whole genome sequencing Asymptomatic reinfection in two healthcare workers from India with genetically distinct SARS-CoV-2 Is novel coronavirus 2019 reinfection possible? Interpreting dynamic SARS-CoV-2 test results through a case report Prolonged detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in an obstetric patient with antibody seroconversion Discontinuation of antiviral drugs may be the reason for recovered COVID-19 patients testing positive again Prolonged presence of SARS-CoV-2 viral RNA in faecal samples Correlation of chest CT. And RT-PCR testing in coronavirus disease 2019 (COVID-19) in China: a report of 1014 cases Chest CT for typical 2019-nCoV pneumonia: relationship to negative RT-PCR testing Evidence summary of the immune response following infection with SARSCoV-2 or other human coronaviruses Kinetics of viral load and antibody response in relation to COVID-19 severity Genomic epidemiology of novel coronavirus -Global subsampling A dynamic nomenclature proposal for SARSCoV-2 lineages to assist genomic epidemiology Convergent antibody responses to SARS-CoV-2 in convalescent individuals Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections