title: Increasing Incidence of Life-threatening Pertussis: A Retrospective Cohort Study in New Zealand.
abstract: Pertussis immunization programs aim to prevent severe infant disease. We investigated temporal trends in infant pertussis deaths and pediatric intensive care unit (PICU) admissions and associations of changes in disease detection and vaccines used with death and PICU admission rates.
  
  
  
  Using national data from New Zealand (NZ), we described infant pertussis deaths and PICU admissions from 1991 to 2013, over which time national immunization coverage at 2 years of age increased from <80% to 92%. In NZ, pertussis became a notifiable disease with polymerase chain reaction (PCR) diagnosis available in 1997 and acellular replaced whole-cell vaccine in 2000. We used Poisson regression to model temporal trends and compared rates in time intervals using rate ratios (RRs) with 95% confidence intervals (CIs).
  
  
  
  There were 10 pertussis deaths and 159 infant PICU admissions with pertussis from 1991 to 2013. The annual number of infant pertussis PICU admissions increased from 1991 to 2013 (P = 0.02) but the number of pertussis deaths did not (P = 0.09). The risk of PICU admission during infancy with pertussis was increased in the notification/PCR versus the non-notification/PCR era (RR: 1.12; 95% CI: 1.02-1.19) and when acellular replaced whole-cell vaccine (RR: 1.19; 95% CI: 1.06-1.31). Median Pediatric Index of Mortality scores during 2001-2013 were lower than during 1991-1999 (P < 0.001).
  
  
  
  Infant PICU pertussis admission rates have increased in NZ despite improvements in immunization coverage. Higher rates have occurred since pertussis notification/PCR became available and since acellular replaced whole-cell vaccine. The severity of disease in infants admitted to PICU with pertussis has decreased in recent years.
authors.affiliation: From the *General Paediatrics, †Paediatric Intensive Care Unit, and ‡Infectious Diseases Departments, Starship Children's Hospital, Auckland District Health Board, Auckland, New Zealand; §Department of Paediatrics, Child & Youth Health, and ¶Department of Statistics, University of Auckland, Auckland, New Zealand; and ‖Nuffield Department of Primary Care Health Sciences, University of Oxford, England, United Kingdom.
authors.forename: Emma
authors.initials: E
authors.lastname: Macdonald-Laurs
authors.forename: Anusha
authors.initials: A
authors.lastname: Ganeshalingham
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lillie
authors.forename: Brent
authors.initials: B
authors.lastname: McSharry
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Segedin
authors.forename: Emma
authors.initials: E
authors.lastname: Best
authors.forename: Avinesh
authors.initials: A
authors.lastname: Pillai
authors.forename: Anthony
authors.initials: A
authors.lastname: Harnden
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Gilchrist
authors.forename: Cameron C
authors.initials: CC
authors.lastname: Grant
mesh_terms: D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009520:New Zealand / Q000453:epidemiology; D012189:Retrospective Studies; D014917:Whooping Cough / Q000453:epidemiology* / Q000401:mortality / Q000517:prevention & control
chemical_list: D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines