title: Predictors of disease severity in children hospitalized for pertussis during an epidemic.
abstract: BACKGROUND
  Australia recently experienced its worst pertussis epidemic since introduction of pertussis vaccine into the National Immunisation Program. This study aimed to determine factors associated with severe pertussis in hospitalized children during an epidemic using a novel pertussis severity scoring (PSS) system.
  
  
  METHODS
  This prospective, observational, multicenter study enrolled children hospitalized with laboratory confirmed pertussis from 8 tertiary pediatric hospitals during a 12 month period (May 2009-April 2010). Variables assessed included demographics, clinical symptoms and relevant medical and immunization history. Cases were scored using objective clinical findings with cases classified as either severe (PSS > 5) or not severe (PSS ≤ 5). Logistic regression models were used to predict variables associated with severe disease.
  
  
  RESULTS
  One hundred twenty hospitalized children 0-17 years of age were enrolled with a median PSS of 5 (interquartile range 3-7). Most (61.7%) were classified as not severe with 38.3% (46/120) severe. Most severe cases (54.3%) were <2 months of age. Presence of coinfection [odds ratio (OR): 4.82, CI: 1.66-14.00], <2 months old (OR: 4.76, CI: 1.48-15.32), fever >37.5°C (OR: 5.97, CI: 1.19-29.96) and history of prematurity (OR: 5.00, CI: 1.27-19.71) were independently associated with severe disease. A total of 70 cases in children ≥2 months of age, almost a third (n = 23) had not received pertussis vaccine.
  
  
  CONCLUSIONS
  Most severe pertussis occurred in young, unimmunized infants, although severe disease was also observed in children >12 months of age and previously vaccinated children. Children admitted with pertussis with evidence of coinfection, history of prematurity or fever on presentation need close monitoring.
authors.affiliation: From the *Robinson Research Institute, Discipline of Paediatrics, School of Paediatrics and Reproductive Health, University of Adelaide; †Vaccinology and Immunology Research Trials Unit, Department of Paediatrics, Women's and Children's Hospital, South Australia, Australia; ‡School of Paediatrics & Child Health, University of Western Australia; §Princess Margaret Hospital for Children; ¶Wesfarmer's Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, Perth, Western Australia, Australia; **SAEFVIC, Murdoch Children's Research Institute, Paediatric Infectious Diseases, Department of Paediatrics, Monash Children's Hospital, Monash University, Victoria, Australia; ††Department of Paediatrics and Child Health, Medical School, Australian National University, Canberra, Australia; ‡‡Menzies School of Health Research, Charles Darwin University, Darwin, Northern Territory, Australia; §§Qpid Laboratory, Queensland Children's Medical Research Institute, Royal Children's Hospital, Brisbane, Australia; and ¶¶National Centre for Immunisation Research and Surveillance, Kids Research Institute, Children's Hospital at Westmead, Sydney, New South Wales, Australia.
authors.forename: Helen
authors.initials: H
authors.lastname: Marshall
authors.forename: Michelle
authors.initials: M
authors.lastname: Clarke
authors.forename: Kavita
authors.initials: K
authors.lastname: Rasiah
authors.forename: Peter
authors.initials: P
authors.lastname: Richmond
authors.forename: Jim
authors.initials: J
authors.lastname: Buttery
authors.forename: Graham
authors.initials: G
authors.lastname: Reynolds
authors.forename: Ross
authors.initials: R
authors.lastname: Andrews
authors.forename: Michael
authors.initials: M
authors.lastname: Nissen
authors.forename: Nick
authors.initials: N
authors.lastname: Wood
authors.forename: Peter
authors.initials: P
authors.lastname: McIntyre
mesh_terms: D000293:Adolescent; D001315:Australia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D058872:Epidemics; D005260:Female; D006760:Hospitalization; D006776:Hospitals, Pediatric; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D062606:Tertiary Care Centers; D014917:Whooping Cough / Q000175:diagnosis* / Q000453:epidemiology / Q000473:pathology*