The infection was first reported last week in Wuhan, a central Chinese city with a population of over 11 million - leading to online speculation about a resurgence of the highly contagious SARS virus.
"We have excluded several hypotheses, in particular the fact that it is a flu, an avian flu, an adenovirus, respiratory syndrome severe acute (SARS) or Middle East Respiratory Syndrome (MERS)," the Wuhan health commission said.
Wuhan police on Wednesday said they had punished eight people for "publishing or forwarding false information on the internet without verification".
The health commission said that seven of the 59 patients are seriously ill but that none have died. All are being treated in quarantine.
The infection broke out between 12 and 29 December, with some of the patients employed at a seafood market in the city that has since been closed for disinfection.
No obvious evidence of human-to-human transmission has been found so far, it added.
The symptoms reported in patients were mainly fever, with a few patients having difficulty in breathing and chest radiographs showing invasive lesions on both lungs.
"The symptoms reported among the patients are common to several respiratory diseases, and pneumonia is common in the winter season," said the WHO, adding that the concentration of cases should be handled "prudently".
It said it was against imposing any travel or trade restrictions on China.
SARS killed 349 people in mainland China and another 299 in Hong Kong in 2003.
The virus, which infected more than 8,000 people around the world, is believed to have originated in the southern Chinese province of Guangdong, according to WHO.
WHO criticised China for under-reporting the number of cases following the outbreak.
China sacked its then health minister Zhang Wenkang for the poor handling of the crisis, several months after the first case was reported.
WHO announced that China was free of SARS in May 2004.