Background
Coronavirus disease (COVID-19) is an acute infectious disease caused by
the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and is
characterized by high morbidity and mortality [1, 2]. COVID-19
outbreak began in China in December 2019 and spread rapidly worldwide,
with the World Health Organization declaring it a pandemic on March 11,
2020. At present, 4,000,000 confirmed cases of COVID-19 have been
detected in more than 200 countries, resulting in more than 280,000
deaths [3], and additional patients with COVID-19 are expected to be
cured and discharged over time. Prevention remains the focus for control
of COVID-19 [4], but the cured or recovered patients should not be
ignored. Currently, little is known about cured COVID-19 patients, and
there are still no guidelines regarding the management of these
patients. However, it is very important to understand the clinical
characteristics of cured patients, especially with respect to
re-infection and person-to-person transmission.
During the immune response activated by the infection, IgM levels are
usually elevated earlier, indicating recent infection and infectivity,
while elevated IgG levels indicate adaptive immunity [5]. However,
in patients with COVID-19, the relevance of IgM and IgG antibodies has
not been clarified. Researches demonstrated that IgM and IgG could be
identified during the early stage of COVID-19, and thus could have a
high diagnostic value in patients with acute infection [6-8].
Compared with real-time reverse transcriptase polymerase chain reaction
(RT-PCR), the detection of antibodies by ELISA is faster, less
expensive, and easier to perform. Therefore, antibody detection might be
widely used to assist in the diagnosis of SARS-CoV-2 infection. Till
date, no study has evaluated the clinical significance of IgM and IgG
detection in terms of re-infection and person-to-person transmission,
especially in COVID-19 patients who were cured and discharged home.