Because of the highly contagious nature of the SARS-Coronavirus (CoV),a rapid and reliable diagnostic test is urgently needed for making a definite diagnosis at early phase so that infected individuals can be isolated while avoiding blanket quarantines and the unnecessary burden on the medical care system.Unfortanantly,current kits/procedures had only less than 20 % positive detecting rate with serum or other samples of real SARS patients.Due to the compositions varies with times and individuals,the septum and lung lavage are impossible to serve as a standardized sample source for the comparison or monitoring of viral load.Therefore,the currently available kits/procedures should be improved and a good sample source should be identified.[Methods] Viral RNA in two hundred microlitter plasma or one million lymphocytes from SARS patients were extracted with Trizol,and then entire RNA was used as a template in a modified procedure of RT-PCR.CoV viral load was quantified in 45 patients at different phases of SARS infection and compared between the paired samples of plasma and lymphocytes obtained from 5 patients who had recovered from SARS for 2 months and lived in a normal life.[Results] Our methods detected CoV at a level of a few copies with 60-80% positive detection rate for plasma from SARS patients within 1 to 7 days after fever,which was much more sensitive than other current available method(positive rate at 8%～20%).The mean viral copies in 17 acute phase patients(1 to 7 days after fever)was 8,951,while that in 18 sub-acute phase patients(13 to 36 days after fever)was 98 and that in 10 recovered patients(79 to 91 days after fever)was 88.Importantly,the levels of CoV in lymphocytes of 5 patients who had recovered from SARS for 2 months were 2 to 3 orders of magnitude higher than that in the plasma.[Conclusions] The early and definite diagnosis of SARS can be achieved by our modified RT-PCR.CoV load peaked during the acute phase and rapidly dropped in sub-acute and recovery phases.The lymphocytes may be the targets or reservoir for CoV and are the best sample source for early SARS diagnosis and the monitoring of CoV infections.
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