Significant risk factors defined for influenza-related complications in children

1. Significant risk factors for hospital admission due to complications from influenza or influenza-like illness in children included neurological disorders, prematurity, sickle cell disease, immunosuppression, diabetes, and age less than 2 years.

2. Reactive airway disease, including asthma, obesity, and ages greater than 2 years were not found to be significant risk factors for hospital admission.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Influenza and influenza-related complications in children are a major public health burden. Recommendations for influenza vaccination in children are currently directed at those at high risk of complications, such as those with underlying medical disorders. However, guidelines do not specifically define risk factors and many are not based on adequate evidence. This study was a systematic review of published and unpublished data used to create an evidence-based definition of certain risk factors in which children would be at an increased risk of developing influenza-related complications.

The results supported current guidelines, showing that significant risk factors for hospital admission were neurological disorders, sickle cell disease, immunosuppression, diabetes, and age less than 2 years, with the addition of prematurity as a new significant risk factor. However, reactive airway disease, including asthma, obesity, and ages greater than 2 years were not found to be significant risk factors. Additionally, the risk of hospital admission was greater in children with multiple risk factors than in children with only one risk factor, when including age less than 2 years as a risk factor. Strengths of this study included specifically focusing on the pediatric population, the use of multivariable analysis, including unpublished data from published studies, and excluding studies at the highest risk for bias. Limitations of this study include that only two studies included in the analysis defined prematurity in terms of gestational age.

Click to read the study in The Lancet

Relevant Reading: Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis

In-Depth [systematic review]: This study searched for studies in Medline, Medline in Process, Embase, Science Citation Index, and CINAHL databases from their inception to April 3, 2013, as well as used unpublished data from published studies, that reported data about risk factors for hospital admission or other complications in children presenting with influenza or influenza-like illness to primary or ambulatory care settings. The primary outcome was hospital admission for influenza or influenza-like illness complications.

28 articles with data from 27 studies (14,086 children) were included in this study, with 3,086 children having an underlying disorder. A meta-analysis of results for hospital admission showed that significant risk factors included neurological disorders (univariable odds ratio [OR] 4.62, 95% Confidence Interval [CI] 2.82-7.55), prematurity (4.33, 2.47-7.58), sickle cell disease (3.46, 1.63-7.37), immunosuppression (2.39, 1.24-4.61), diabetes (2.34, 1.20-4.58), and age less than 2 years (2.51, 1.71-3.69). Reactive airway disease, including asthma (1.36, 0.82-2.26), obesity (0.99, 0.61-1.62), and older age groups, including ages 2-5 (0.89, 0.67-1.17) and ages 5-18 (0.61, 0.44-0.85), were not determined to be significant risk factors for hospital admission. An individual patient data meta-analysis of 1,612 children from four studies showed that neurological disorders, immunological disorders, prematurity, and age less than 2 years were independent risk factors for hospital admission. Children with only one type of disorder (48% [186 of 291]) were hospitalized less than children with multiple disorders (74% [29 of 39]; difference 27%; 95% CI 12-41%, p=0.001). When using age less than 2 years as a risk factor, hospitalization increased from 52% (428 of 817) of children with one condition to 74% (92 of 124) of children with more than one condition (difference 22%; 95% CI 13-30, p<0.0001).

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