New York: More evidence is emerging that coronavirus infections are being spread by people who have no clear symptoms, complicating efforts to gain control of the pandemic.

A study conducted by researchers in Singapore and published by the US Centres for Disease Control and Prevention on Wednesday is the latest to estimate that around 10 per cent of new coronavirus infections may be sparked by people who were infected with the virus but not experiencing symptoms.

Italy's Foreign Minister Luigi Di Maio receives a letter from a Turkish army officer as Italian soldiers unload donated personal protection equipment in Rome. Credit:AP

In response to recent studies, the CDC changed how it was defining the risk of infection for Americans.

The agency's new guidance, also released on Wednesday, targets people who have no symptoms but were exposed to persons with known or suspected infections. It essentially says that anyone may be a considered a carrier, whether they have symptoms or not.