Results
A total of 296 patients were diagnosed with COVID-19 from January 20, 2020 to March 10, 2020. Among these patients, one died, two were still hospitalized, seven were under 18 years old, 48 refused to perform antibody test, and 51 were transferred or discharged to other hospitals for treatment (Figure 1). Altogether, 187 patients were screened and followed up at least once in our hospital and subsequently followed up till April 10, and they were included in the final analysis. The mean follow-up time was 45.7 days.
We found that the patients in the IgG positive group were older (49.1 vs. 43.2, P = 0.031), hospitalized longer (21.0 vs. 14.0,P < 0.001), had more severe disease (18.2 vs. 3.0,P = 0.049), and with higher proportion of antibiotics treatment (88.3 vs. 63.6, P = 0.001) than in the negative group (Table 1). There was no difference between the two groups in terms of transmission source, incubation period, and comorbidities (all P> 0.05). The complications of COVID-19 included acute respiratory distress syndrome (ARDS), septic shock, acute liver failure, acute renal failure, and acute heart injury. There was no difference between the IgG positive group and negative group with regard to complications (all P > 0.05). No differences were found in the treatment comprised mechanical ventilation, glucocorticoids, intensive care between the two groups (all P> 0.05).
Potential variables, including age (OR, 1.03; 95% CI, 1.00-1.06;P = 0.033), hospitalization days (OR, 1.08; 95% CI, 1.03-1.13;P = 0.003), severe disease (OR, 7.11; 95% CI, 0.93-54.26;P = 0.058), abnormal chest CT (OR, 3.75; 95% CI, 0.80-17.62;P = 0.094), and antibiotics treatment (OR, 3.09; 95% CI, 1.28-7.48; P = 0.012) , that might be associated with antibody production were screened by using univariate logistic regression analyses (Table 2). In the multivariate logistic regression model, determinants associated with antibody production comprised hospitalization days (OR: 1.07, 95%CI: 1.02-1.13, P = 0.004) and antibiotics treatment (OR: 2.78, 95%CI: 1.10-7.01, P= 0.031) .
Out of these 187 patients, 35 (18.7%) patients showed positive results and 152 (81.3%) showed negative results for IgM (Table 3). There were 154 (82.4%) patients with positive results and 33 (17.6%) patients with negative results for IgG. The antibody tests were performed after 53 days on an average from the date of disease onset. Of the 35 IgM positive cases, 12 cases turned negative during the follow up. PCR assays were undertaken in all patients using both pharyngeal and anal swabs. They yielded two positive pharyngeal swabs, seven positive anal swabs, and one positive result for both pharyngeal and anal swabs. On further retesting, all the positive results of PCR assays were found to be negative.
In the IgG positive group, eight patients demonstrated positive results on PCR from two pharyngeal swabs and six anal swabs. In the IgG negative group, one patient had positive pharyngeal swabs and one both pharyngeal and anal swabs. We found no relationship between IgG test and PCR assay. Of the 35 IgM positive patients, two had positive anal swabs and no pharyngeal swabs. There was no relationship between IgM test and PCR assay. No re-infection occurred in any patient after discharge and no medical staffs were infected during the treatment. Among people who were in close contact with the cured patients, no one was diagnosed with COVID-19, as reported by both the cured patients and the Guangzhou CDC.