The process of viral shedding and its relevance to effective screening for infectious disease.
Viral Shedding before and after symptom onset

The research paper, “Temporal dynamics in viral shedding and transmissibility of COVID-19”, presents the process of viral shedding across the presymptomatic and symptomatic phases. The researchers provide significant insight into the presymptomatic stage and the priority of identifying individuals who are infected prior to symptom expression. The ability to identify individuals prior to symptom onset is a key differentiator for Viral Sign.

Key findings from the paper:

  • Presymptomatic, pre-elevated body temperature transmission represents at least 44% of viral transmissions, consistent with prior research with suggest the presymptomatic state may lead to as many as 58% of all transmissions of ILI.
  • Viral transmission can begin as early as 12 days before elevated body temperature expression, but is highly unlikely this early in these disease process.
  • The greatest potential for virus transmission occurs in the presymptomatic state (three days prior to fever expression) and continues to the day of fever expression.
Viral Shedding before and after symptom onset

Highlights from the authors:

“Assuming an incubation period distribution of mean 5.2 days from a separate study of early COVID-19 cases1, we inferred that infectiousness started from 12.3 days (95% CI, 5.9–17.0 days) before symptom onset and peaked at symptom onset (95% CI, –0.9–0.9 days) (Fig. 1c). We further observed that only <0.1% of transmission would occur before 7 days, 1% of transmission would occur before 5 days and 9% of transmission would occur before 3 days prior to symptom onset. The estimated proportion of presymptomatic transmission (area under the curve) was 44% (95% CI, 30–57%). Infectiousness was estimated to decline quickly within 7 days.”

“In conclusion, we have estimated that viral shedding of patients with laboratory-confirmed COVID-19 peaked on or before symptom onset, and a substantial proportion of transmission probably occurred before first symptoms in the index case. More inclusive criteria for contact tracing to capture potential transmission events 2 to 3 days before symptom onset should be urgently considered for effective control of the outbreak.”

The full article can be referenced via the web at https://www.nature.com/articles/s41591-020-0869-5.