The World Health Organization believes it is likely that both of the suspect SARS cases in Guangdong Province, China, are suffering from SARS, but that additional laboratory tests are needed before full laboratory confirmation can be made.
Blood samples from the waitress in Guangzhou have been analysed in the two WHO-affiliated SARS reference laboratories in Hong Kong, SAR. Results from these tests show that the woman has high levels of antibodies capable of neutralizing the SARS coronavirus and that, as her illness progressed, there was a four-fold increase in these antibody levels - indicating she has suffered from SARS and hence should be considered to be a confirmed case. Similar findings were found when the same samples were tested in laboratories in Beijing, China.
However, a note of caution was raised by one of the laboratories in Hong Kong, SAR, after a similar rise in antibodies in this patient were found to another, more common coronavirus - OC43, which causes common cold in humans. Further work should be done to fully understand the significance of this. Attempts should be made to isolate the SARS coronavirus, and to test all appropriate samples with PCR. For this reason, WHO has requested that more samples be sent to the laboratories in Hong Kong, SAR, to conduct those tests.
In the case of the 35-year-old businessman in Guangzhou, blood samples have also been tested in the laboratories in Hong Kong, SAR. Results from these tests indicate that he too has antibodies that neutralize the SARS coronavirus, as well as antibodies to the non-SARS coronavirus OC43 (mentioned above in the other case). However, the blood samples that were sent to the two laboratories in Hong Kong were taken in the early part of his illness, and were separated by only three days. It has therefore been impossible, at this stage, to show the four-fold rise in antibody levels -- the internationally accepted indicator of acute infection. WHO has therefore requested that further samples be sent to the laboratories in Hong Kong, SAR, to be tested in an attempt to display the necessary rise in antibodies and to exclude cross-reaction with OC43 through the use of PCR and virus isolation.
Whilst there are clinical and laboratory indications to suggest the 35-year-old man may have SARS, at this stage the laboratory results from the patient do not meet the WHO criteria for laboratory confirmation. Therefore, this patient should remain a suspect case.
WHO will continue to monitor developments in these cases and provide updates in the days ahead.