Background Antibody responses to virus reflect exposure and potential protection. Methods We developed a highly specific and sensitive approach to measuring antibodies against SARS-CoV-2 for population-scale immune surveillance. Antibody positivity was defined as a dual-positive response against both the receptor binding domain and nucleocapsid proteins of SARS-CoV-2. Antibodies were measured by immuno-precipitation assays in capillary blood from 15,771 children aged 1 to 18 years living in Bavaria, Germany, and participating in a public health type 1 diabetes screening program (Clinicaltrials.gov NCT04039945) , in 1,916 dried blood spots from neonates in a Bavarian screening study ( Clinicaltrials.gov NCT03316261) , and in 75 SARS-CoV-2 positive individuals. Virus positive incidence was obtained from Bavarian health authority data. Findings. Dual-antibody positivity was detected in none of 3887 children in 2019 (100% specificity) and 73 of 75 SARS-CoV-2 positive individuals (97.3% sensitivity). Antibody surveillance in children during 2020 resulted in frequencies of 0.08% in January to March, 0.61% in April, 0.74% in May, 1.13% in June and 0.91% in July. Antibody prevalence from April 2020 was six-fold higher than the incidence of authority-reported cases (156 per 100,000 children), showed marked variation between the seven Bavarian regions ( P <0.0001), and was not associated with age or sex. Transmission in children with virus-positive family members was 35%; 47% of positive children were asymptomatic. No association with type 1 diabetes autoimmunity was observed. Antibody frequency in newborns was 0.47%. Conclusion We demonstrate the value of population-based screening programs for pandemic monitoring. Funding. The work was supported by funding from the BMBF (FKZ01KX1818).

Increased activities of certain biochemical enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], lactate dehydrogenase [LDH], alkaline phosphatase [ALP]) have been associated with blunt liver injury in many species. To evaluate changes in plasma hepatic biochemical parameters in acute avian liver disease caused by trauma and to compare biochemical changes with histologic lesions in hepatic parenchyma, 30 healthy fasted Indian ring-necked parakeets (Psittacula krameri manillensis) were divided into 2 groups, and traumatic liver injury was caused by endoscopic liver biopsy (group 1) or by liver biopsy and crushing injury to the hepatic parenchyma with endoscopic forceps (group 2) in anesthetized birds. Blood samples were collected at baseline and at 12, 24, 36, 48, 60, 72, 84, 96, 108, and 120 hours in alternate groups to compare analyte values after injury with those at baseline. Results showed consistently decreased plasma ALP activity (excluding 1 time point) throughout the study, which was thought to be associated with isoflurane administration. Plasma glutamate dehydrogenase activity initially increased but rapidly declined thereafter and was attributed to acute focal hepatocellular injury. In both groups, increases in plasma AST, ALT, and LDH activities was most likely caused by muscle injury because creatine kinase activity was concurrently increased. Compared with baseline values, bile acid concentration and y-glutamyl transferase activity were not affected by liver biopsy or crush injury. Plasma sorbitol dehydrogenase activity was the most specific indicator of liver injury in both groups. Histologic changes correlated poorly with biochemical results, possibly because the small area of hepatic parenchyma that was damaged did not affect enzyme values substantially.