title: [A three-year follow-up study on sera specific antibody in severe acute respiratory syndrome cases after the onset of illness].
abstract: OBJECTIVE
  To study the variation of specific antibody among convalescent of severe acute respiratory syndrome (SARS) patients through a three-year program.
  
  
  METHODS
  Sera samples were collected from SARS cases in the 5th, 20th and 35th month after onset of the illness. The SARS-CoV specific antibody was detected for all of them by ELISA and neutralized test simultaneously. The titer of neutralizing antibodies was calculated using Reed-Muench method, and the comparison between different time groups was analyzed regarding the variance of data on repeated measures after logarithm conversion.
  
  
  RESULTS
  13, 17 and 13 sera samples were collected in the 5th, 20th and 35th month after onset. Results showed that despite the fact that the positive rates of ELISA antibody were 100%, 82.4% and 84.6% respectively,the neutralizing antibody was still positive for all the samples. The average neutralizing antibody titers were 1:43 (1:16-1:203), 1:36 (1:17-1:59) and 1:21 (1:10-1:39) on the 5th, 20th and 35th month after onset, and the differences were statistically significant (F = 60.419, P < 0.001). On the 35th month after the onset, 30.8% (4/13) of the patients were still having the neutralizing antibody level of above 1:36, but the neutralizing antibody level in another 30.8% (4/13) of the patients had decreased to as low as 1:10, when the cut-off level was set as 1:8.
  
  
  CONCLUSIONS
  Results of the study indicated that the neutralizing antibody of SARS cases could last for at least three years, but the sera specific antibody in SARS cases decreased gradually when time went by. However, neutralizing antibody in some of the cases decreased to a lower level on the 35th month. Further follow-up study was worthwhile to observe the long-lasting profile of antibody existence on SARS cases.
authors.affiliation: Department of Epidemic Control and Prevention, Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou 310009, China.
authors.forename: Shu-yun
authors.initials: SY
authors.lastname: Xie
authors.forename: Guang
authors.initials: G
authors.lastname: Zeng
authors.forename: Shi-chang
authors.initials: SC
authors.lastname: Xia
authors.forename: Pan-he
authors.initials: PH
authors.lastname: Zhang
authors.forename: Wei-dong
authors.initials: WD
authors.lastname: Yin
authors.forename: Bi-yao
authors.initials: BY
authors.lastname: Liu
authors.forename: Shi-gui
authors.initials: SG
authors.lastname: Yang
authors.forename: Wu-chun
authors.initials: WC
authors.lastname: Cao
mesh_terms: D057134:Antibodies, Neutralizing / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay; D005500:Follow-Up Studies; D006801:Humans; D045169:Severe Acute Respiratory Syndrome / Q000276:immunology*
chemical_list: D057134:Antibodies, Neutralizing