1706 JID 2004 190 1 November CORRESPONDENCE 1 NOVEMBER Correspondence Figure 1 Severe acute respiratory syndrome associated coronavirus immunoglobulin SARS CoV Ig titers measured over the course of 1 year in 62 survivors of SARS shown are mean titers with 95 confidence intervals A and in 1 asymptom atic infected health care worker B Natural Course of Severe Acute Respiratory Syndrome Associated Coronavirus Immunoglobulin after Infection To the Editor In Chen et al s recent study severe acute respiratory syndrome SARS associated coronavirus SARS CoV IgG was shown to be persistent for up to 60 days 1 Their results suggested that production of this antibody is dependent on CD4 cells and might play a role in protective immunity against SARS CoV On the other hand IgM has been found to decrease and become undetectable 11 weeks into the recovery phase 2 Whether survivors of SARS can have persistent an tibody and lifelong immunity against SARS CoV is unknown We conducted a 1 year prospective study to investigate the natural course of SARS CoV immunoglobulin titer in 62 survivors of SARS and in 1 asymptomatic infected health care worker as described in our previous reports 3 4 All of the serologic tests were performed at the Gov ernment Virus Unit Hong Kong Chi na following a standard protocol Serum samples were diluted 1 25 and 15 mLof the diluted samples were incubated by use of microscopic slides coated with SARS CoV infected fetal rhesus kidney cells in a moist chamber for 30 min at 37H11034C The slides were then washed with 2 changes of Tween 20 Sigma Fifteen microliters of polyvalent anti human immunoglobulin labeled with fluorochrome was added and the slides were incubated again for 30 min at 37H11034C This was followed by another wash with 2 changes of Tween 20 The slides were then examined by use of a fluo rescence microscope under a low power field 20H11003 Any positive signals showing cytoplasmic fluorescence were confirmed by examination under a high power field 40H11003 and all tests with indeterminate re sults were repeated with uninfected cells to exclude nonspecific reactions Results were quantified by use of serial titrations of serum samples from patients and were reported as titers 25 25 50 100 200 400 800 1600 and 3200 For all of the survivors of SARS in our study serum samples were collected on the day of admission to the hospital and 15 days 1 month 3 months 6 months 9 months and 12 months after the onset of SARS symptoms The mean age of the sur vivors of SARS was 37 07 years SD 12 96 years and the male female ratio was 0 82 On admission to the hospital all of them had a baseline SARS CoV immunoglob ulin titer 25 Fifteen days after the onset of symptoms the mean SARS CoV im munoglobulin titer was 252 8 figure 1A at 1 and 3 months after the onset of symp toms the mean SARS CoV immunoglob ulin titer had increased to 613 3 and 880 3 respectively Afterward a gradual decrease in the mean SARS CoV immunoglobulin titer was observed to 167 7 at 12 months after the onset of symptoms i e a 5 3 fold decrease in mean titer at 12 months after the onset of symptoms compared with the mean titer at 3 months after the onset of symptoms For the asymptom atic infected health care worker serum samples were collected 1 3 6 9 and 12 months after the first day she was de ployed to the SARS ward Her first SARS CoV immunoglobulin titer was 400 fig ure 1B which decreased to 50 at 3 and 6 months after deployment i e an 8 fold decrease in titer At 9 and 12 months af ter deployment her SARS CoV immuno globulin titer was only 25 A previous study has reported that over time neutralizing antibody against other CoVs can decay to an undetectable level 5 In SARS the human antibody against the S1 spike protein of SARS CoV has been shown to have a neutralizing effect 6 Our findings have shown that survivors of SARS experience a minimum 5 fold de crease in SARS CoV immunoglobulin titer over 9 months and the asymptomatic in fected health care worker in our study ex perienced an even more rapid decrease in SARS CoV immunoglobulin titer It re mains to be seen whether SARS CoV im munoglobulin will finally disappear in in fected persons The progressive decrease in SARS CoV immunoglobulin titer im plies that over time infected persons may experience a decrease in protective im munity against SARS CoV Convalescent serum has been used to treat patients with at Washburn University on March 17 2015 http jid oxfordjournals org Downloaded from CORRESPONDENCE JID 2004 190 1 November 1707 SARS in Hong Kong and other parts of China because it is expected that survivors of SARS have high levels of SARS CoV immunoglobulin 7 On the basis of the findings of our study convalescent serum ideally should be collected from donors 3 months after the onset of symptoms the time at which the yield of SARS CoV immunoglobulin would be the highest Eugene Y K Tso 1 Owen T Y Tsang 1 Bosco Lam 2 T K Ng 2 Wilina Lim 3 and Thomas S T Lai 1 1 Department of Medicine and Geriatrics and 2 Department of Pathology Princess Margaret Hospital and 3 Government Virus Unit Department of Health Hong Kong China References 1 Chen X Zhou B Li M et al Serology of severe acute respiratory syndrome implications for surveillance and outcome J Infect Dis 2004 189 1158 63 2 Chen W Xu Z Mu J et al Antibody response and viraemia during the course of severe acute respiratory syndrome SARS associated co ronavirus infection J Med Microbiol 2004 53 435 8 3 Tso EYK Tsang OTY Choi KW et al Persis tence of physical symptoms in and abnormal laboratory findings for survivors of severe acute respiratory syndrome letter Clin Infect Dis 2004 38 1338 4 Lee HK Tso EY Chau TN Tsang OT Choi KW Lai TS Asymptomatic severe acute re spiratory syndrome associated coronavirus infection Emerg Infect Dis 2003 9 1491 2 5 Wesley R Neutralizing antibody decay and lack of contact transmission after inocula tion of 3 and 4 day old piglets with porcine respiratory coronavirus J Vet Diagn Invest 2002 14 525 7 6 Sui J Li W Murakami A et al Potent neu tralization of severe acute respiratory syn drome SARS coronavirus by a human mAb to S1 protein that blocks receptor associa tion Proc Natl Acad Sci USA 2004 101 2536 41 7 Wong VW Dai D Wu AK Sung JJ Treatment of severe acute respiratory syndrome with con valescent plasma Hong Kong Med J 2003 9 199 201 Reprints or correspondence Dr Eugene Y K Tso Infectious Diseases Team Dept of Medicine and Geriatrics Princess Mar garet Hospital Lai Chi Kok Hong Kong China eugene88 The Journal of Infectious Diseases 2004 190 1706 7 H17050 2004 by the Infectious Diseases Society of America All rights reserved 0022 1899 2004 19009 0025 15 00 Reply to Tso et al To the Editor We appreciate the letters from Tso et al 1 2 that expand on our study 3 of the serologic profile of severe acute respiratory syndrome SARS On the basis of the findings of our study we are certain that IgG antibody persists for at least 60 days after the onset of symp toms This is consistent with Tso et al s results which despite the different assays used indicate that SARS associated co ronavirus SARS CoV immunoglobulin titers continue to increase from 15 days to 3 months after the onset of symptoms Interestingly the rate of seroconversion differs in the 2 studies with an 83 rate of seroconversion reported in our study and a 100 rate of seroconversion re ported in Tso et al s study 2 This may have been a consequence of the different populations of patients and of the differ ent assays used in the studies Tso et al selected 62 survivors from a group of 267 patients with SARS among whom 78 had a 4 fold increase in SARS CoV im munoglobulin or a single titer of H11091100 during their first 3 months of follow up 2 4 This 78 rate of seroconversion in the 267 patients 4 was close to our ob servations of 75 on day 21 and 83 on day 60 According to several reports the immunofluorescent assay used by Tso et al is more sensitive than the ELISA used in our study 5 7 Nevertheless ELISA provides similar results and remains the most convenient and reliable test in both clinical practice and epidemiologic studies Xinchun Chen a Boping Zhou Meizhong Li Xiaorong Liang Huosheng Wang Guilin Yang Hui Wang and Xiaohua Le Shenzhen Municipal Hospital of Infectious Disease Shenzhen Guangdong China References 1 Tso EYK Tsang OTY Lam B Ng TK Lim W Lai TST Natural course of severe acute respi ratory syndrome associated coronavirus im munoglobulin after infection letter J Infect Dis 2004 190 1706 7 in this issue 2 Tso EYK Tsang OTY Choi KW et al Persis tence of physical symptoms in and abnormal laboratory findings for survivors of severe acute respiratory syndrome letter Clin Infect Dis 2004 38 1338 3 Chen X Zhou B Li M et al Serology of severe acute respiratory syndrome implications for surveillance and outcome J Infect Dis 2004 189 1158 63 4 Choi KW Chau TN Tsang O et al Outcomes and prognostic factors in 267 patients with se vere acute respiratory syndrome in Hong Kong Ann Intern Med 2003 139 715 23 5 Wu HS Chiu SC Tseng TC et al Serologic and molecular biologic methods for SARS as sociated coronavirus infection Taiwan Emerg Infect Dis 2004 10 304 10 6 National Research Project for SARS Beijing Group Serum antibodies detection for sero logical diagnosis of severe acute respiratory syn drome in Chinese Zhonghua Jie He He Hu Xi Za Zhi 2003 26 339 42 7 Chan PK Ng KC Chan RC et al Immuno fluorescence assay for serologic diagnosis of SARS Emerg Infect Dis 2004 10 530 2 a Present affiliation Department of Pediatrics University of Ar izona Tucson Reprints or correspondence Dr Xinchun Chen Dept of Pedi atrics University of Arizona Rm 5356 1501 N Campbell Tuc son AZ 85724 chenxinchun The Journal of Infectious Diseases 2004 190 1707 H17050 2004 by the Infectious Diseases Society of America All rights reserved 0022 1899 2004 19009 0026 15 00 at Washburn University on March 17 2015 http jid oxfordjournals org Downloaded from