Can asymptomatic people spread coronavirus disease 2019 (COVID-19)?

Updated: Jun 25, 2021
  • Author: David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS; Chief Editor: Michael Stuart Bronze, MD  more...
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Oran and Topol [43] published a narrative review of multiple studies on asymptomatic SARS-CoV-2 infection. Such studies and news articles reported rates of asymptomatic infection in several worldwide cohorts, including resident populations from Iceland and Italy, passengers and crew aboard the cruise ship Diamond Princess, homeless persons in Boston and Los Angeles, obstetric patients in New York City, and crew aboard the USS Theodore Roosevelt and Charles de Gaulle aircraft carrier, among several others. They found that approximately 40-45% of SARS-CoV-2 infections were asymptomatic. 

Utilizing a decision analytical model, Johansson et al from the US Centers for Disease Control and Prevention assess transmission from presymptomatic, never symptomatic, and symptomatic individuals across various scenarios to determine the infectious period of transmitting SARS-CoV-2. Results from their base case determined 59% of all transmission came from asymptomatic transmission, comprising 35% from presymptomatic individuals and 24% from individuals who never develop symptoms. They estimate at least 50% of new SARSCoV-2 infections originated from exposure to individuals with infection, but without symptoms. [44]  

Zou and colleagues [45] followed viral expression through infection via nasal and throat swabs in a small cohort of patients. They found increases in viral loads at the time that the patients became symptomatic. One patient never developed symptoms but was shedding virus beginning at day 7 after presumed infection. 

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