Influenza-attributable mortality was significantly greater in children with influenza B, compared with influenza A, investigators found.
Among those with influenza B, patients aged 10-16 years were most likely to require ICU admission, suggesting this subpopulation may be a target for immunization programs.
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The percentage of clinical cases attributed to influenza B range from less than 1% to 44%, according to data published by the Centers for Disease Control and Prevention. However, influenza B is considered less virulent and less capable of causing pandemics and has therefore been less studied and outcomes of its disease less characterized, Dat Tran, MD, MSc, of the Hospital for Sick Children in Canada and his associates reported (Pediatrics. 2016 August. doi: 10.1542/peds.2015-4643).
The purpose of this study was to further understand the prevalence and severity of influenza B cases in comparison with influenza A and to identify pediatric subpopulations most at risk for contracting influenza B.
Children aged 16 years or younger hospitalized from laboratory-confirmed influenza A or B from September 2004 to June 2013 (excluding the pandemic year 2009-2010) were identified through active surveillance of admissions at the 12 pediatric referral centers of the Canadian Immunization Monitoring Program Active (IMPACT), a national surveillance initiative. Information regarding demographics, health status, vaccination status, presenting signs and symptoms, illness severity and mortality, treatment regimens, and ICU admission were collected and analyzed.
Of 4,155 influenza-related admissions during this time period, influenza B accounted for 1,510 (36.3%) cases and influenza A accounted for 2,645 (63.7%) cases.
Children admitted with influenza B tended to be older with a median age 3.9 years (interquartile range, 1.4-7.2), compared with a median of 2 years (IQR, 0.6-4.8 years) for children admitted with influenza A.
Children admitted with influenza B, compared with influenza A, had higher odds of having a vaccine-indicated condition (odds ratio, 1.30; 95% confidence interval, 1.14-1.47) and lower odds of having no underlying medical condition (OR, 0.80; 95% CI, 0.71-0.91), Dr. Tran and his associates reported.
“Compared with influenza A cases, children admitted with influenza B had greater adjusted odds of presenting with headache, abdominal pain, and myalgia, ranging from 1.38 for abdominal pain to 3.19 for myalgia,” they added. “There were no significant differences in antiviral or antibiotic prescription or use between influenza A and B cases.”
There was no significant difference in the proportion of influenza A or B patients admitted to the ICU (12.7% vs. 12.6%). Rather, multivariate modeling identified age and presence of an underlying condition as independent predictors of ICU admission.
Finally, influenza-attributable mortality was significantly greater in children with influenza B (adjusted OR, 2.65; 95% CI, 1.18-5.94). Influenza-attributable mortality occurred in 16 (1.1%) children with influenza B and only 10 (0.4%) children with influenza A. All-cause mortality followed a similar trend.
“Among hospitalized children, influenza A and B infections resulted in similar morbidity while mortality was greater for influenza B disease. Among healthy children hospitalized with influenza B, those aged 10-16 years were most likely to require ICU admission,” the investigators summarized.
“These children should be considered at high risk for complicated influenza B infection and be specifically targeted by immunization programs to receive influenza vaccination, and in particular, a [quadrivalent influenza vaccine],” they recommended.
This study was funded by GlaxoSmithKline Biologicals SA. The Canadian Immunization Monitoring Program Active is funded by the Public Health Agency of Canada. The investigators reported having no relevant disclosures.