High SARS-CoV-2 Household Transmission Rates Detected by Dense Saliva Sampling

Background: Understanding the dynamics of SARS-CoV-2 household transmission is important for adequate infection control measures in this ongoing pandemic. Methods: Households were enrolled upon a PCR-confirmed index case between October and December 2020, prior to the COVID-19 vaccination programme. Saliva samples were obtained by self-sampling at day 1, 3, 5, 7, 10, 14, 21, 28, 35, and 42 from study inclusion. Nasopharyngeal swabs (NPS) and oropharyngeal swabs (OPS) were collected by the research team at day 7 and capillary blood samples at day 42. Household secondary attack rate (SAR) and per-person SAR were calculated based on at least one positive saliva, NPS, OPS, or serum sample. Findings: Eighty-five households were included consisting of 326 (unvaccinated) individuals. Comparable numbers of secondary cases were identified by saliva (133/241; 55·2%) and serum (127/213; 59·6%). The household SAR was 88·2%. The per-person SAR was 64·3%. The majority of the secondary cases tested positive in saliva at day 1 (103/150; 68·7%). Transmission from index case to household member was not affected by age or the nature of their relationship. Interpretation: Households have a pivotal role in SARS-CoV-2 transmission. By repeated saliva self-sampling combined with NPS, OPS, and serology, we found the highest SARS-CoV-2 household transmission rates reported to date. Salivary (self-)sampling is suitable for monitoring of SARS-CoV-2 transmission. Salivary sampling of all household members in the first week after symptom onset or positive test of a household index case may assist in infection control in this ongoing pandemic. Funding Information: This work was supported by The Netherlands Organization for Health Research and Development, ZonMw, grant number 10430012010017. ZonMw, Laan van Nieuw Oost Indië 334, 2593 CE The Hague, The Netherlands.Declaration of Interests: The authors declare no conflicts of interest involving the work under consideration for publication.Ethics Approval Statement: This study was reviewed and approved by the Medical Ethical Committee of the Vrije Universiteit university Medical Centre (VUmc), The Netherlands (reference number 2020.436). Written informed consent was obtained from all participating household members and/or their legal guardians when below the age of 16 years.