Background Household studies are crucial for understanding the transmission of SARS-CoV-2 infection, which may be underestimated from PCR testing of respiratory samples alone. We aim to combine assessment of household mitigation measures; nasopharyngeal, saliva and stool PCR testing; along with mucosal and systemic SARS-CoV-2 specific antibodies, to comprehensively characterise SARS-CoV-2 infection and transmission in households. Methods Between March and September 2020, we obtained samples from 92 participants in 26 households in Melbourne, Australia, in a 4-week period following onset of infection with ancestral SARS-CoV-2 variants. Results The secondary attack rate was 36% (24/66) when using nasopharyngeal swab (NPS) PCR positivity alone. However, when respiratory and non-respiratory samples were combined with antibody responses in blood and saliva, the secondary attack rate was 76% (50/66). SARS-CoV-2 viral load of the index case and household isolation measures were key factors that determine secondary transmission. In 27% (7/26) of households, all family members tested positive by NPS for SARS-CoV-2 and were characterised by lower respiratory Ct-values than low transmission families (Median 22.62 vs 32.91; IQR 17.06 to 28.67 vs 30.37 to 34.24). High transmission families were associated with enhanced plasma antibody responses to multiple SARS-CoV-2 antigens and the presence of neutralising antibodies. Three distinguishing saliva SARS-CoV-2 antibody features were identified according to age (IgA1 to Spike 1, IgA1 to nucleocapsid protein (NP), suggesting that adults and children generate distinct mucosal antibody responses during the acute phase of infection. Conclusion Utilising respiratory and non-respiratory PCR testing, along with measurement of SARS-CoV-2 specific local and systemic antibodies, provides a more accurate assessment of infection within households and highlights some of the immunological differences in response between children and adults.

Background There are limited data in paediatric populations evaluating whether chronic cardiorespiratory conditions are associated with increased risk of COVID-19. We aimed to compare the rates of chronic cardiac and respiratory disease in children testing positive (SARS-CoV-2[+]) compared to those testing negative (SARS-CoV-2[-]) at our institution. Method Prospective cohort with nested case-control study of all children tested by PCR for SARS-CoV-2 by nasopharyngeal/oropharyngeal sampling between March and October 2020. Children were identified prospectively via laboratory notification with age and sex-matching of SARS-CoV-2[+] to SARS-CoV-2[-] (1:2). Clinical data were extracted from the electronic medical record. Results In total, 179 SARS-CoV-2[+] children (44% female, median age 3.5 yrs, range 0.1 to 19.0 yrs) were matched to 391 SARS-CoV-2[-] children (42% female, median age 3.7 yrs, range 0.1 to 18.3 yrs). The commonest co-morbidities showed similar frequencies in the SARS-CoV-2[+] and [-] groups: asthma (n = 9, 5% vs n = 17, 4.4%, p = 0.71), congenital heart disease (n = 6, 3.4% vs n = 7, 1.8%, p = 0.25) and obstructive sleep apnoea (n = 4, 2.2% vs n = 10, 2.3%, p = 0.82). In the SARS-CoV-2 group, the prevalence of symptomatic disease was similar amongst children with and without cardiorespiratory comorbidities (n = 12, 75% vs n = 103, 57%, p = 0.35) who tested positive. A high proportion of children hospitalised with SARS-CoV-2 infection had cardiac comorbidities (23.8%). Conclusions In this single site dataset, rates of pre-existing cardiorespiratory disease were similar in SARS-CoV-2[+] and SARS-CoV-2[-] children. High rates of comorbid cardiac disease were observed amongst hospitalised children with COVID-19, warranting further research to inform public health measures and vaccine prioritisation.