Health workers in China have ruled out severe acute respiratory syndrome (SARS) as the cause of a mysterious respiratory illness that afflicted dozens of people in Wuhan City.

That's a small bit of relief for officials, because SARS killed hundreds of people in an outbreak in China a decade ago.  But the Wuhan Municipal Health Commission says investigators have also ruled out Middle East respiratory syndrome (MERS), influenza, bird flu, and adenovirus.  

Doctors diagnosed 59 patients with the unexplained, pneumonia-like illness, and placed them in isolation; seven of them are in a critical condition.  

Most of the patients have common symptoms such as fever, difficulty breathing, and lung lesions appearing in a "small number'' of cases.  Many of the patients worked at Wuhan's South China Seafood market, which officials promptly closed and ordered disinfected.  Fifteen patients in Hong Kong were being treated for symptoms after recent visits to Wuhan.

But despite these clusters, there's actually no evidence of human-to-human transmission.  

The United Nations World Health Organization (WHO) says it is monitoring the situation.