Dynamic changes of throat swabs RNA and serum antibodies for SARS-CoV-2 and their diagnostic performances in patients with COVID-19

Abstract

Dynamic changes of RNA and antibodies in SARS-CoV-2 infected patients remain largely unknown, and influence factors for antibody production have not been fully clarified. In this study, consecutive throat swabs specimens (n = 1875) from 187 patients were collected to analyse the dynamic changes of RNA. Moreover, 162 serial serum samples from 31 patients were tested for seroconversion of IgM and IgG. Meanwhile, IgM and IgG were also detected in 409 COVID-19 patients and 389 controls. Additionally, the logistic regression analysis was executed to identify the possible influence factors for antibody production. The median positive conversion time for RNA was day 7 (IQR, 3-11), and the positive rate was highest in day 1-5 (74.59 %) and then gradually decreased. The median time of seroconversion for IgM and IgG were both day 12 (IQR, 10-15). The sensitivity and specificity for IgM (or IgG) was 87.04% and 96.92%, respectively. Multivariate logistic regression indicated that reduced lymphocytes and short positive conversion time for SARS-CoV-2 RNA were independent factors for negative results of IgM and IgG. In conclusion, RNA and antibodies should be combined for COVID-19 diagnosis, and delayed seroconversion was influenced by the decreased lymphocytes and short positive conversion time for RNA.

Keywords: Antibody; COVID-19; RNA; SARS-CoV-2; throat swabs.

Figure 1.

The positive rates of RNA and antibodies among COVID-19 patients in different time durations since symptoms onset. The positive rate of RNA was analysed in 1875 throat swab specimens from 187 COVID-19 confirmed patients. The positive rate of antibodies was analysed in 409 serum samples from 409 COVID-19 confirmed patients.

Figure 2.

Positive conversion of RNA and antibodies against SARS-CoV-2 in COVID-19 patients. Cumulative positive rates of patients with COVID-19 for RNA and antibody (IgM, IgG) were displayed by courses of the disease. The scale on the right of the figure shows the positive rate level indicated with different colours, the blue corresponds to a low positive rate and the red to a high positive rate. The lower table presents the number of samples that tested positive at each time point.

Figure 3.

The longitudinal changes of antibody and RNA in 10 representative patients with COVID-19. The red solid square represents the positive result of RNA, the green solid square represents the negative result of RNA, and the black solid square represents no sample was collected.

Figure 4.

Lymphocyte counts in different subtypes of COVID-19 patients. Independent-samples t test was used to comparison the variables in different groups. * p < 0.05, ** p < 0.01, **** p < 0.0001.