False-positive SARS-CoV-2 serology in three children with Kawasaki disease

To, Kelvin KW; Chua, Gilbert T.; Kwok, Ka Li; Wong, Joshua SC; Au, Dennis Chi Yu; Lam, Yuen Yu; Wong, Wilfred HS; Ho, Marco HK; Chan, Godfrey CF; Chui, Celine SL; Li, Xue; Tung, Keith TS; Wong, Rosa S; Tso, Winnie WY; Wong, Ian CK; Wong, Christina SM; Fong, Carol HY; Chan, Kwok Hung; Yuen, Kwok Yung; Ip, Patrick; Kwan, Mike YW

BACKGROUND: Kawasaki disease (KD) is an acute febrile and eruptive disease with systemic vasculitis predominantly affecting young East Asian children. Recent reports showed that children with KD-like disease from KD low prevalence regions had positive SARS-CoV-2 serology despite a negative SARS-CoV-2 polymerase chain reaction (PCR) in respiratory samples. OBJECTIVES: To describe three pediatric Kawasaki Disease patients with false positive SARS-CoV-2 serology. STUDY DESIGN: We retrospectively recruited children with KD diagnosed during the COVID-19 outbreak in Hong Kong. Clinical characteristics and laboratory test results including SARS-CoV-2 PCR results were retrieved. We performed a microparticle-based immunoassay for the detection of IgG against nucleoprotein (NP) and spike protein receptor binding domain (RBD), and a microneutralization assay for the detection of neutralizing antibodies. RESULTS: Three Chinese children with typical KD were identified. They had no epidemiological links with COVID-19 patients and tested negative for SARS-CoV-2 NPA PCR. They were treated with IVIG and aspirin, and were discharged without complications. Subsequently two of them were tested positive against anti-RBD and anti-NP antibodies and one was tested positive against anti- RBD antibodies. However, microneutralization assay showed that neutralizing antibodies were absent, suggesting a false-positive IgG result. CONCLUSION: Detection of neutralizing antibodies is recommended to confirm previous SARS-CoV-2 infection in IgG-positive but PCR-negative patients.