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Increasing Incidence of Life-threatening Pertussis: A Retrospective Cohort Study in New Zealand

Macdonald-Laurs, Emma MBChB; Ganeshalingham, Anusha MB BS; Lillie, Jonathan MB BS; McSharry, Brent MB BS; Segedin, Elizabeth R. FRACP; Best, Emma FRACP; Pillai, Avinesh MSc; Harnden, Anthony FRCPCH; Gilchrist, Catherine A. PhD; Grant, Cameron C. FRACP

The Pediatric Infectious Disease Journal: March 2017 - Volume 36 - Issue 3 - p 282–289
doi: 10.1097/INF.0000000000001441
Original Studies
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Background: 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.

Methods: 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).

Results: 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).

Conclusions: 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.

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.

Accepted for publication August 10, 2016.

E.M. reports grants from Glaxo-Smith-Kline, outside the submitted work. The Department of Paediatrics at the University of Auckland funds C.A.G.’s medical writer position. C.C.G. had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

E.B. is a member of the Antiinfectives Subcommittee of PHARMAC’s Pharmacology and Therapeutics Advisory Committee, which provides advice on funding restrictions, safety and implementation of new antiinfectives to the New Zealand government. C.C.G. reports to and is a member of the Immunisation Subcommittee of PHARMAC’s Pharmacology and Therapeutics Advisory Committee, which provides advice to the New Zealand government on vaccines to be included in the national immunization schedule. The other authors have no conflicts of interest to disclose.

Address for correspondence: Cameron C. Grant, FRACP, Department of Paediatrics, Child and Youth Health, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Wellesley Street, Auckland 1142, New Zealand. E-mail: cc.grant@auckland.ac.nz.

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