A hospital worker wears a mask as a precaution against the MERS virus at Seoul National University Hospital in Seoul, South Korea, Friday, June 12, 2015.

SEOUL--The World Health Organization said on Saturday South Korea's outbreak of Middle East Respiratory Syndrome (MERS) was "large and complex" and more cases should be anticipated, but it saw no sign the disease is spreading in the community.

There was also no indication that the MERS virus in South Korea had changed to make it more transmissible, the WHO's assistant director general, Keiji Fukuda, told a news conference at the Health Ministry in Sejong, south of the capital, Seoul.