Epidemiology of Australian Influenza-Related Paediatric Intensive Care Unit Admissions, 1997-2013

Marlena C. Kaczmarek, Robert S. Ware, Mark G. Coulthard, Julie McEniery, Stephen B. Lambert

Influenza virus predictably causes an annual epidemic resulting in a considerable burden of illness in Australia. Children are disproportionately affected and can experience severe illness and complications, which occasionally result in death. We conducted a retrospective descriptive study using data collated in the Australian and New Zealand Paediatric Intensive Care (ANZPIC) Registry of influenza-related intensive care unit (ICU) admissions over a 17-year period (1997-2013, inclusive) in children <16 years old. National laboratory-confirmed influenza notifications were used for comparison. Between 1997 and 2013, a total of 704 influenza-related ICU admissions were recorded, at a rate of 6.2 per 1,000 all-cause ICU admissions. Age at admission ranged from 0 days and 15.9 years (median = 2.1 years), with 135 (19.2%) aged <6 months. Pneumonia/pneumonitis and bronchiolitis were the most common primary diagnoses among influenza-related admissions (21.9% and 13.6%, respectively). More than half of total cases (59.2%) were previously healthy (no co-morbidities recorded), and in the remainder, chronic lung disease (16.7%) and asthma (12.5%) were the most common co-morbidities recorded. Pathogen co-detection occurred in 24.7% of cases, most commonly with respiratory syncytial virus or a staphylococcal species. Median length of all ICU admissions was 3.2 days (range 2.0 hours- 107.4 days) and 361 (51.3%) admissions required invasive respiratory support for a median duration of 4.3 days (range 0.2 hours- 107.5 days). There were 27 deaths recorded, 14 (51.9%) in children without a recorded co-morbidity. Influenza causes a substantial number of ICU admissions in Australian children each year with the majority occurring in previously healthy children.