Recovered SARS Patient Continues to Shed Virus in Stool --------------------------------------------------- An issue that has not been discussed anywhere in ProMED-mail in detail (perhaps because little is known about it) is that of continual viral shedding by clinically recovered SARS patients. A colleague of mine in Singapore, who has had the SARS illness and was diagnosed with the SARS coronavirus by RT-PCR culture and electron microscopy, has informed me that SARS coronavirus RNA has continued to be detected in stool samples by RT-PCR, although it has not yet been successfully grown in culture. This continued for sometime after the quarantine period of 10-14 [days?] after recovery from illness (up to 3 weeks post-recovery). If such is the case for most -- or even some -- of the recovered SARS patients, perhaps this may account for the ongoing transmission we are seeing in places like Singapore in household and workplace contacts of clinically recovered SARS patients. Perhaps the laboratories of the WHO collaborating network should ask for convalescent stool samples as well as sera to monitor and characterise this phenomenon.
[The current RT-PCR tests utilize primers that amplify short sequences of the polymerase gene of the putative SARS coronavirus. These tests may do no more than detect the presence of defective virus in gut contents. The replication of many RNA viruses is accompanied by the progressive accumulation of defective interfering particles (the equivalent of deletion mutants), which are thought to be a determining factor in the self-limiting characteristics of some acute virus infections. The failure to isolate infectious virus from the patient after recovery suggests that transmission of SARS via gut contents post-recovery does not represent substantial risk. Nonetheless, it is not possible to discount this route of transmission of SARS virus without knowledge of the relative sensitivity of the cell culture employed, and Dr. Julian Tang has drawn attention to an important question. - Mod.CP]
http://www.promedmail.org/pls/askus/f?p=2400:1001:102727813954567900::NO::F2400_P1001_BACK_PAGE,F2400_P1001_PUB_MAIL_ID:1000,21428
Maybe it's the number of viruses a person comes into contact with that makes the difference, and infection from recovered patients' stools is relatively low.
The interesting thing is that recovery isn't dependent on elimination of the virus. It has to be based upon sufficient antibodies being developed, or some other protective measure.
Or maybe the fact that these shed viruses haven't been successfully grown in culture yet is an indication that they've been somehow neutralized genetically. Just guessing here.