Initial Research

The epidemic of severe atypical pneumonia which was observed in the Chinese province of Guangdong and reported internationally on Feb- ruary 11, 2003 (WHO, WER 11/2003), was initially suspected to be linked to a newly emerging influenza virus: on February 19, 2003, researchers isolated an avian influenza A (H5N1) virus from a child in Hong Kong. This virus was similar to the influenza virus originating from birds that caused an outbreak in humans in Hong Kong in 1997, and new outbreaks of similar strains were expected. However, bird 'flu', possibly of poultry origin, was soon ruled out as the cause of the newly-termed Severe Acute Respiratory Syndrome, or SARS.

Investigations then focused on members of the Paramyxoviridae family, after paramyxovirus-like particles were found by electron microscopy of respiratory samples from patients in Hong Kong and Frankfurt am Main. Further investigations showed that human metapneumovirus (hMPV; van den Hoogen) was present in a substantial number of, but not in all, SARS patients reported at the time.

At about the same time, China reported the detection, by electron microscopy, of Chlamydia-like organisms in patients who had died from atypical pneumonia during the Guangdong outbreak. Again, this finding could not be confirmed by other laboratories in SARS patients from outside China.