Supplemental Digital Content 1. Socio-demographic, laboratory and clinical characteristics of 613 Australian children aged under 15 years hospitalized with severe complications of laboratory-proven influenza (2008-2017)
Confirmed cases N = 613* (%)
Male 333 (54.4%)
Median age at hospitalization (range) years 3.4 (0-14) Median time between symptom onset and
admission (days) 3 (IQR 1-5)
Median duration of hospital stay (days) 5 (IQR 2-11)
Australian born 500 (81.6%)
Ethnicity
Caucasian 354 (57.7%)
Asian 54 (8.8%)
ATSI 48 (7.8%)
Middle Eastern 32 (5.2%)
Pacific Islander 25 (4.1%)
African 11 (1.8%)
Other 39 (6.4%)
Unknown 50 (8.2%)
SEIFA quintiles
Most disadvantaged 106 (18.3%)
Second quintile of disadvantage 85 (14.7%) Third quintile of disadvantage 127 (21.9%) Fourth quintile of disadvantage 151 (26.1%)
Least disadvantaged 110 (19.0%)
Remoteness Index (ARIA)
Major cities of Australia 430 (74.1%)
Inner regional 92 (15.9%)
Outer, remote or very remote 58 (10.0%)
Influenza type
Influenza A 419 (68.6%)
Influenza A sub-types
H1N1 99 (23.6%)
H3 24 (5.7%)
H1N1-09 (17) and SOIV (2) 19 (4.5%)
H3N2 5 (1.2%)
Not H1N1 5 (1.2%)
H1 2 (0.5 %)
Negative for H1N1 or H3N3 1 (0.2%)
No subtype found/not tested 264 (63.1%)
Influenza B 191 (31.3%)
Both Influenza A and B 1 (0.2%)
Contacts and travel
Contact with confirmed influenza case 29 (4.8%) Child travelled overseas in the 10 days before
onset of the symptoms 8 (1.3%)
Child had close contact with farm animals 8 (1.3%) Symptoms present at admission
Symptoms/signs of influenza like illness
Fever 522 (85.2%)
Cough 472 (77.0%)
Dyspnea 283 (45.7%)
Malaise/lethargy 262 (42.7%)
Sore throat 79 (12.9%)
Coryza 19 (3.1%)
Rhinorrhea 10 (1.6%)
Apnea 9 (1.5%)
Stridor 4 (0.7%)
Wheeze 4 (0.7%)
Bronchiolitis 4 (0.7%)
Croup 4 (0.7%)
Asthma 3 (0.5%)
Earache 3 (0.5%)
Pleuritic chest pain 2 (0.3%)
Nasal congestion 2 (0.3%)
Hemoptysis 2 (0.3%)
Rhinitis 2 (0.3%)
Respiratory distress 1 (0.2%)
Other symptoms
Vomiting 187 (30.5%)
Seizure/unconsciousness 87 (14.2%)
Diarrhea 70 (11.4%)
Headache 67 (10.9%)
Myalgia 59 (9.6%)
Confusion/Disorientation 47 (7.7%)
Rash 27 (4.4%)
Other† 81 (13.2%)
Underlying medical conditions
At least one underlying medical condition‡ 247 (40.3%)
Neurological disorders 83 (13.5%)
Asthma 60 (9.8%)
Chronic lung disease (excludes asthma, cystic
fibrosis) 41 (6.7%)
Neuromuscular disorder 28 (4.6%)
Congenital heart disease 20 (3.3%)
Immunodeficiency 15 (2.4%)
Malignancy 10 (1.6%)
Cystic fibrosis 1 (0.2%)
Other chronic illness 63 (10.3%)
Vaccination status§
Seasonal influenza vaccine last 12mth
(N=353) 30 (8.5%)
H1N1 vaccine (2010-2011) 2 (0.2%)
Pneumococcus vaccine(N=372) 301 (80.9%) Antiviral treatment (N=584) 211 (36.1%) Oseltamivir (N=210)
Oseltamivir within 2 days 33 (15.7%)††
Oseltamivir within 5 days 64 (30.5%)††
Commencement date not reported 118 (19.2%)
ARIA: Accessibility- Remoteness Index of Australia, ATSI: Aboriginal and Torres Strait Islander, IQR: Interquartile Range, SEIFA: Socio-Economic Indexes for Areas.
* One case was hospitalized twice with a different influenza infection.
† Other symptoms included:, weight loss, decreased oral intake, vertigo, ataxia, metabolic acidosis, inability to walk, syncope, severe dehydration, sepsis, decreased oral intake and poor feeding, poor perfusion, altered level of consciousness, neck pain, lactic acidosis, jaundice, abdominal pain, irritability, insomnia, hypotension, hyponatremia, hyperkalemia, hyperglycemia, hepatomegaly, hemiparesis, hematuria, hematemesis, melena, dizziness, dysarthria, conjunctivitis, cardiac arrest, aphonia and diabetic ketoacidosis.
‡ Defined as having any underlying medical condition.
§ Recommended in Australian children ≥6 months of age.