‘The scientific community is still uncovering the full picture of SARS-CoV-2 transmission dynamics. A study published in The Lancet: Infectious Diseases analyzed SARS-CoV-2 transmission among clusters in Catalonia, Spain, to understand the relationship between viral load and transmission risk. The researchers utilized participant data from a previous clinical trial, and they identified 314 COVID-19 patients that met their inclusion criteria. Among those patients, 282 had at least 1 contact (753 total contacts). The index patients infected 125 secondary cases, corresponding to a secondary attack rate of 17%.
‘The researchers identified a statistically significant association between viral load in the index patients and the subsequent secondary attack rate. Among index patients with the lowest viral load, index patients exhibited a secondary attack rate of 12%, compared to 24% among the highest group. The researchers estimate that the odds of secondary transmission increase 30% for every log(10) increase in viral load. Additionally, the study found increased likelihood that secondary cases would develop COVID-19 symptoms associated with increased viral load in the index patients (aHR of 1.12 per log(10) increase in viral load). While further research is needed to more fully characterize the factors associated with transmission, this study provides evidence that the index patient’s viral load could be a major driver of secondary transmission risk and potentially disease severity in secondary cases.’ (Source: Updates on the COVID-19 pandemic from the Johns Hopkins Center for Health Security.)
Transmission of COVID-19 in 282 clusters in Catalonia, Spain: a cohort study
Read original here (The Lancet, Feb 2, 2021)
