Cross-reaction of sera from COVID-19 patients with SARS-CoV assays.

Wei Yee Wan; Siew Hoon Lim; Eng Hong Seng

is the (which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.03.17.20034454 doi: medRxiv preprint showed that overall the IIFA test was 28.9% more sensitive than the ELISA test, which explains 100 the results of day 24 for P3. Although the overall results for the IIFA test may be more sensitive, 101 the IIFA IgM test in the COVID-19 patients was found to be less useful in the detection of acute 102 phase of the illness which is consistent with the findings of a study in SARS-CoV patients where 103 they found a less frequent (43%) and robust (less discriminatory) IgM response. 13 However, this 104 cannot be generalized as different assays will have different performances depending on the type 105 of antigen utilized. In most countries, real-time RT-PCR remains the diagnostic tool of choice in 106 the acute phase of infection given that antibody will take time to develop after the onset of 107 illness. These serological tests would be more useful in those who did not present early to a 108 healthcare facility to look for evidence of previous exposure to this virus. This is relevant for 109 contact tracing and to determine the true extent of the circulation of the virus to establish an 110 accurate case-fatality rate.