Q: Why is there an ~20-30% false negative rate with the PCR test for #SARS_CoV2 ?
A: Mostly due to sampling as explained by @PSampathkumarMD @MayoClinic
Thread 1/2 https://www.news18.com/news/world/many-people-who-have-tested-negative-for-covid-19-might-actually-have-it-warn-scientists-2573267.html

1. The nasopharynx is a tricky place to get a sample from
2. The virus may have already passed from the upper to the lower respiratory system. (ie a sputum sample would be a better testing specimen
2/2