ABSTRACT
The main objective of this study was to estimate the performance, under local epidemiological conditions, of two in-house ELISA assays for the combined detection of anti-SARS-CoV-2 IgA, IgM, and IgG immunoglobulins. A total of 94 serum samples were used for the assessment, where 44 corresponded to sera collected before the pandemic (free SARS-CoV-2 antibodies), and 50 sera were collected from confirmed COVID-19 patients admitted to the main public hospital in the city of Valdivia, southern Chile. The Np and RBD proteins were separately used as antigens (Np and RBD ELISA, respectively) to assess their diagnostic performance. A receiver operating characteristic (ROC) analysis was performed to estimate the optical density (OD) cut-off that maximized the sensitivity (Se) and specificity (Sp) of the ELISA assays. Np ELISA had a mean Se of 94% (95% CI = 83.5 - 98.8%) and a mean Sp of 100% (95% CI = 92.0 - 100%), with an OD 450 nm positive cut-off value of 0.88. On the other hand, RBD ELISA presented a mean Se of 96% (95% CI = 86.3 - 99.5%) and a mean Sp of 90% (95% CI = 78.3 - 97.5%), with an OD 450 nm positive cut off value of 0.996. Non-significant differences were observed between the Se distributions of Np and RBD ELISAs, but the latter presented a significant lower Sp than Np ELISA. In parallel, collected sera were also analyzed using a commercial lateral flow chromatographic immunoassay (LFCI), to compare the performance of the in-house ELISA assays against a commercial test. The LFCI had a mean sensitivity of 94% (95% CI = 87.4 - 100%) and a mean specificity of 100% (95% CI = 100 - 100%). When compared to Np ELISA, non-significant differences were observed on the performance distributions. Conversely, RBD ELISA had a significant lower Sp than the LFCI. Although, Np ELISA presented a similar performance than the commercial test, this was 2.5 times cheaper than the LFCI assay. Thus, the in-house Np ELISA could be a suitable alternative tool, in resource limited environments, for the surveillance of SARS-CoV-2 infection, supporting further epidemiological studies.
Subject(s)
COVID-19ABSTRACT
During the first pandemic wave Covid-19 reached Latin America cities. Aim: To report clinical features and outcomes associated to Covid-19 in a group of patients admitted during the first wave in a regional reference Center in southern Chile designated to severe and critical cases. Methods: Cases were identified by a compatible clinical picture associated to positive RT-PCR or serological testing. A standard protocol was applied. Results: 21 adult patients (20 diagnosed by PCR, one by serology) were admitted between epidemiological weeks 13 to 20, involving 8.8% of total regional cases. Hospitalization occurred at a median of 11 days after symptoms onset. Patients [≥]60 years old predominated (57.1%). Hypertension (61.9%), obesity (57.1%) and diabetes mellitus 2 (38.1%) were prevalent but 19% had no comorbid conditions nor were elderly. Two cases involved second-trimester pregnant women. Positive IgM or IgM/IgG results obtained by rapid serological testing were limited (19% at 1st week; 42.9% at 2nd week). Nine patients (42.9%, critical group) were transferred to ICU and connected to mechanical ventilation due to respiratory failure. By univariate analysis admission to ICU was significantly associated to tachypnea and higher plasmatic LDH values. One pregnant woman required urgent cesarean section given birth to a premature neonate without vertical transmission. Two patients died (in-hospital mortality 9.5%) and length of stay was equal or higher than 14 days in 57.9% of patients. Conclusion: In our regional Center, Covid 19 was associated to known risk factors, had a prolonged stay and in-hospital mortality. Tachypnea [≥]30/min is predictive of transfer to ICU.