Washington, July 13 : Around 40 per cent of the confirmed coronavirus cases in the US were asymptomatic, according to the country's Centers for Disease Control and Prevention (CDC). The revelation was made on Sunday in the CDC's latest "COVID-19 Pandemic Planning Scenarios" document, Xinhua news agency reported. The document, which the agency said can be used to estimate the possible effects of COVID-19 in US states and localities, was first posted on May 20. The latest update is based on data received by the CDC through June 29. The new percentage of infections that are asymptomatic, under the CDC's "current best estimate", is up from the 35 per cent the agency estimated on May 20. Also, under the agency's current best estimate, an asymptomatic individual is 75 per cent as infectious as a symptomatic individual. "Asymptomatic cases are challenging to identify because individuals do not know they are infected unless they are tested, which is typically only done systematically as a part of a scientific study," the CDC added. The US has witnessed a sudden surge in the number of COVID-19 cases, especially in states like California, Texas, Arizona and Florida. According to the Johns Hopkins University, the country currently accounts for the world's highest number of infections and fatalities at 3,302,665 and 135,176, respectively, /IANS