Levels and influencing factors of serum pertussis toxin-IgG antibody in children with pertussis / 中华传染病杂志

ABSTRACT

Objective:To investigate the levels and influencing factors of serum pertussis toxin (PT)-IgG antibody in children with pertussis.Methods:The clinical data including age, course of disease and vaccination status of children with laboratory-confirmed pertussis and tested for PT-IgG antibody in Shenzhen Children′s Hospital from July 2015 to December 2018 were collected. Venous blood samples were obtained to detect PT-IgG antibody levels. Nasopharyngeal swabs were taken for polymerase chain reaction (PCR) test to detect Bordetella pertussis nucleic acid and culture of Bordetella pertussis. Mann-Whitney U test was used for comparison between two groups.Kruskal-Wallis test was used for comparison among multiple groups. Multiple linear regression was used to analyze the influencing factors of PT-IgG antibody levels. Results:A total of 871 children aged 4(2, 7) months were included, among whom, 592(68.0%) cases were under six months and 754 (86.6%) cases were under one year old. The course of disease was 15 (11, 20) days. Among 871 cases, 864 (99.2%) cases were PCR test and (or) culture positive, including 696 cases positive only for PCR test, 35 cases positive only for culture and 133 cases positive for both PCR test and culture. There were 452 (51.9%) children who were not vaccinated and 346 (39.7%) children vaccinated with at least one dose. In terms of age, the PT-IgG amtibody levels of children aged 0 to two months, three to five months, six months to two years and ≥three years were 0.7 (0, 8.2) IU/mL, 2.3 (0, 23.0) IU/mL, 24.6 (0, 112.3) IU/mL and 24.9 (0, 114.7) IU/mL, respectively. The PT-IgG antibody levels of children after onset of symptoms at 0 to two weeks, more than two to four weeks, more than four to eight weeks and more than eight weeks were 0(0, 7.9) IU/mL, 8.7(0, 56.0) IU/mL, 26.6(5.1, 82.9) IU/mL and 68.0(15.3, 118.8) IU/mL, respectively. The differences were both statistically significant ( H=88.346 and 94.076, respectively, both P<0.01). The PT-IgG antibody levels in children who were unvaccinated and vaccinated with at least one dose were 0.9 (0, 12.7) IU/mL and 14.6(0, 86.3) IU/mL, respectively. The difference was statistically significant ( Z=-8.520, P<0.01) PT-IgG≥80 IU/mL accounted for 16%(139/871) in the whole range of age, 34.3%(12/35) in children ≥three years old. There were 13 patients aged ≥three years old with a disease course >two weeks, among whom, six patients had PT-IgG≥80 IU/mL. Age, course of disease and vaccination status were independent influencing factors of PT-IgG levels ( β=0.108, 0.189 and 0.250, respectively, all P<0.01). Conclusions:The levels of PT-IgG antibody in children with pertussis are influenced by age, course of disease and vaccination status. The single serum PT-IgG of 80 IU/mL as cut-off value in the diagnosis of pertussis may lead to a increase of missed diagnosis. Therefore, it is necessary to further explore the standards suitable for children in China.