human-to-human transmission
Health officials worry as untraceable virus clusters emerge
In South Korea, Singapore and Iran, clusters of infections are leading to a jump in cases of the new viral illness outside China. But it's not the numbers that are worrying experts: It's that increasingly they can't trace where the clusters started.
WHO says no clear evidence of human-to-human transmission of novel coronavirus
Despite the first exported case of novel coronavirus from the Chinese city of Wuhan, the World Health Organization (WHO) said Tuesday that there is no clear evidence of human-to-human transmission based on available information.