mikkasprzak
commented
4 years ago This is really tricky. This is what the US agency CDC says:
Several studies have documented SARS-CoV-2 infection in patients who never develop symptoms (asymptomatic) and in patients not yet symptomatic (pre-symptomatic). Since asymptomatic persons are not routinely tested, the prevalence of asymptomatic infection and detection of pre-symptomatic infection is not yet well understood. One study found that as many as 13% of reverse transcription-polymerase chain reaction (RT-PCR)-confirmed cases of SARS-CoV-2 infection in children were asymptomatic. Another study of skilled nursing facility residents who were infected with SARS-CoV-2 after contact with a healthcare worker with COVID-19 demonstrated that half of the residents were asymptomatic or pre-symptomatic at the time of contact tracing, evaluation, and testing.Patients may have abnormalities on chest imaging before the onset of symptoms.
This is what the European agency says: Asymptomatic infection at time of laboratory confirmation has been reported from many settings [52,142-147]. Some of these cases developed some symptoms at a later stage of infection [148,149]. In a recent review, the proportion of positive cases that remained asymptomatic was estimated at 16%, with a range from 6 to 41% [150]. In another systematic review, the pooled proportion of asymptomatic cases at time of testing was 25% [151]. A majority of these cases developed symptoms later on, with only 8.4% of the cases remaining asymptomatic throughout the follow-up period [151]. There are also reports of asymptomatic cases with laboratory-confirmed viral shedding in respiratory and gastrointestinal samples [148,152,153]. Similar viral loads in asymptomatic versus symptomatic cases have been reported, indicating the potential of virus transmission from asymptomatic patients [154].
Asymptomatic transmission (i.e. when the infector has no symptoms throughout the course of the disease), is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers for the growth of the COVID-19 pandemic. Although transmission from asymptomatic carriers has been reported, the risk of transmission from pre-symptomatic or symptomatic patients is considered to be higher. Viral RNA shedding is higher at the time of symptom onset and declines after days or weeks. Pre-symptomatic transmission (i.e. when the infector develops symptoms after transmitting the virus to another person) has been reported. Exposure of secondary cases occurred 1–3 days before the source patient developed symptoms. It has been inferred through modelling that, in the presence of control measures, pre-symptomatic transmission contributed to 48% and 62% of transmissions in Singapore and China, respectively. Pre-symptomatic transmission was deemed likely based on a shorter serial interval of COVID-19 (4.0 to 4.6 days) than the mean incubation period (five days).
Major uncertainties remain with regard to the influence of pre-symptomatic transmission on the overall transmission dynamics of the pandemic because the evidence on transmission from asymptomatic cases from case reports is suboptimal.
How to incorporate asymptotic cases into the model?