Analysis Of High Factors Of Severe And Desth In Infants With Pertussis And Research On The Virulence Related Genes Of Clinical Isolates

Part 1.Analysis of high risk factors associated with severe pertussis in infantsBackground:Pertussis is a highly infectious human acute respiratory disease,which is caused by the Gram-negative bacteria,Bordetella pertussis.It is characterized by paroxysmal cough,which ends with vomiting,apnea or cyanosis.Severe cases may cause respiratory failure,pulmonary hypertension,pertussis encephalopathy and even death,and treatment measures are limited.It is an important cause of child death in the world.Method:In order to understand the epidemiological characteristics of pertussis patients and the high risk factors for the development of severe pertussis,and to provide the basis for early clinical identification of severe cases,we collected all clinical data of children with pertussis diagnosed in children’s Hospital Affiliated to Chongqing Medical University from January 2013 to July 2019,and divided them into severe group and non severe group for retrospective case-control study.Patients with pertussis were confirmed by clinical and laboratory examination.Severe pertussis is defined as death or admission to a pediatric intensive care unit(PICU)due to pertussis infection.Result:In order to eliminate the age-related heterogeneity,63 infants< 120 days of age with severe pertussis were selected and compared with 64 non severe pertussis cases <120 days of age,randomly selected from the system according to the ratio of 1:1.Univariate regression analysis showed that the risk factors associated with severe disease included age of 1-2 months(P =0.001),premature delivery(P = 0.02),hospital weight(P = 0.011),fever(P<0.01),wheezing(P<0.01),length of hospital stay(P<0.01),maximum lymphocyte count(P = 0.005),and leukocytosis(leukocyte count)≥30×109/ L(P = 0.001)or ≥50×109/L(P<0.01),the highest platelet count(P<0.01),the highest heart rate(P<0.01),pulmonary consolidation(P<0.01),combined with definite pathogenic infection(P < 0.01),convulsion(P =0.015),pertussis encephalopathy(P<0.01),IVIG(P = 0.003)and hormone therapy(P = 0.018). The multivariate analysis revealed that fever(or 3.848,95% CI1.083-13.668,P = 0.037),leukocytosis(or 4.101,95% CI 1.25-13.454,P =0.02),pulmonary consolidation(or 6.051,95% CI 1.67-21.927,P = 0.006)and infection with definite pathogen(or 6.663,95% CI 2.101-21.128,P =0.001)were significantly associated with severe pertussis.Conclusion:Fever,leukocytosis,pulmonary consolidation and infection with definite pathogen were independent risk factors for severe pertussis.Therefore,early clinical identification of potential severe pertussis,active treatment of infection,is expected to reduce the incidence of severe pertussis.Part 2.Risk factors associated with death in infants with severe pertussisBackground:Pertussis is a serious infectious disease in young infants,and severe cases frequently cause death.Our study explored risk factors for death from severe pertussis.Method:A case-control study of infants with severe pertussis admitted to the paediatric intensive care unit(PICU)in the Children’s Hospital of Chongqing Medical University,China,from January 1,2013,to June 30,2019,was conducted.Pertussis was confirmed by clinical features and laboratory examinations.Severe pertussis was defined as patients with pertussis resulting in PICU admission or death.To understand the risk factors for death,we compared fatal and nonfatal cases of severe pertussis in infants aged < 120 days by collecting clinical and laboratory data.Results:The participants included 63 infants < 120 days of age with severe pertussis.Fifteen fatal cases were confirmed and compared with 44 nonfatal severe pertussis cases,Four patients with termination of treatment were excluded.In the univariate analysis,the risk factors associated with death included apnoea(P= 0.001),leukocytosis(white blood cell(WBC)count≥30×109/L(P=0.001)or≥50×109/L(P < 0.01),highest lymphocyte count(P<0.01),pulmonary hypertension(P= 0.001),and length of PICU stay(P= 0.003).The multivariate analysis revealed that apnoea(OR 23.722,95%CI 2.796–201.26,P= 0.004),leukocytosis(OR 63.708,95%CI3.574–1135.674,P= 0.005)and pulmonary hypertension(OR 26.109,95%CI 1.800–378.809,P= 0.017)were significantly associated with death.Conclusion:Leukocytosis and pulmonary hypertension exhibited the greatest associations with death in infants with severe pertussis admitted to the PICU.Vaccination is still the most effective protection method against pertussis.Part 3.Research On The Virulence Related Genes of Bacillus pertussis in patients with severe pertussisBackground:In addition to the recognized as risk factors of severe pertussis,such as host factors and leukocytosis,recent studies have emphasized the potential role of Virulence Related Genes in the pathogenesis of severe pertussis.Method:A total of 720 samples were collected from patients with pertussis admitted to children’s Hospital of Chongqing Medical University,from September 2016 to June 2019.Nasopharynx swab secretions were collected for pertussis culture,A total of 126 strains of Bordetella pertussis were isolated and cultured.In order to further understand the virulence related genotypes of strains isolated from patients with leukocytosis,21 patients with leukocytosis(the highest leukocyte count ≥30×109/L)were studied retrospectively.At the same time,the whole genome sequencing of 3 severe pertussis strains and 3 non severe pertussis strains were sequenced,compared and analyzed.Result:Among the 126 strains of Bordetella pertussis,21(16.7%)were leukocytosis and 105(83.3%)were non leukocytosis;Among the strains with leukocytosis in the course of disease,3 strains were diagnosed as severe pertussis,and 18 strains(85.7%)were non severe.The average maximum white blood cell count of 21 patients was 48.05 ± 18.24×109/L,The highest WBC count was 95.75×109/L in No.92 strains.the child was diagnosed as severe and died.Other patients improved after treatment.The Virulence Related Genes of most strains(18 / 21,85.7%)were ptx P1/ptx A1/ ptxC1/ prn1/ fim2-1/ fim3-1/ tcf A2,and 3 strains(14.2%)were ptx P3/ ptx A1/ ptxC2/ prn1/ fim2-1/ fim3-1/ tcf A2.Among the severe strains,The Virulence Related Genes of 2 strains were ptx P3/ ptxC2 and 1strain was ptx P1/ ptxC1.Conclusion From 2016 to 2019,the Virulence Related genotype of pertussis was still ptx P1/ptx A1/ptxC1/prn1/fim2-1/fim3-1/ tcf A2.Among the 3 strains diagnosed as severe pertussis,The Virulence Related Genes of 2 strains were ptx P3 / ptxC2.