The impact of influenza B (FLUB) was relatively less researched than influenza A (FLUA), because of its lower pandemic potential. We aimed to compare the clinical presentations and disease severity between FLUA and B. This study involved children hospitalized with virologically-confirmed influenza between 2010-2020. The disease severity was assessed according to admission to the intensive care unit (ICU), mechanical ventilation requirement, length of hospital, and ICU stay and death. FLUA and B were compared within predefined age groups (0-2, 3-9, and 10-18 years) and in all age groups. Of 343 patients, FLUA and B were detected in 260 (75.8%) and 83 (24.2%) children, respectively. Headache and abdominal pain were more common in FLUB (P<0.05). Children with FLUA were prescribed antibiotics and antivirals 1.6 and 2.3-fold more than those with FLUB. From subgroup analysis by age, patients between 3-9 with FLUB had a higher rate of headache and abdominal pain; additionally, headache occurred in 5 (100%) children aged 10-18 years with FLUB and 10 (38.5%) with FLUA (P<0.05). Children between 0-2 with FLUA were more often admitted to ICU than those with FLUB (22.9% vs. 6.0%; P<0.05). Eight patients with FLUA died, and one with FLUB (P>0.05). The clinical presentation was similar between FLUA and B, except for headache and abdominal pain, which were notably more common in older patients with FLUB. Children aged 0-2 years with FLUA had a significant risk for ICU admission. Higher levels of awareness and attention should be paid to children under two years with FLUA.

Objective: To determine whether viral coinfection is a risk for severe lower respiratory tract infection (LRTI). Working Hypothesis: Children with viral coinfection had a higher risk for admission to the intensive care unit (ICU) than those with a single virus infection. Study Design: Retrospective, observational study for ten years. Patient-Subject Selection: Children between 1-60 months of age hospitalized with LRTI. Methodology: We defined severe LRTI as admission to the ICU for high-flow nasal cannula oxygen/bilevel positive airway pressure/invasive ventilation and assessed demographic and laboratory data with potential risk factors from the patients’ medical records. Results: Of 2115 children hospitalized with LRTI, 562 had severe, and 1553 had mild disease. Viral coinfection was present in 28.3% of all patients, and those with viral coinfection were at a higher risk of severe LRTI than those with a single virus infection (43.8% vs. 22.7%; aOR, 3.44; 95% CI, 2.74-4.53). Respiratory syncytial virus (RSV) and rhinovirus (except for between 25-60 months) coinfections were associated with severe LRTI in all ages, whereas parainfluenza virus-3 (PIV3; 7-24 months) and bocavirus (7-12 months) coinfections led to severe LRTI in early childhood. Moreover, influenza-A coinfection caused severe LRTI in children between 7-12 and 25-60 months. Other risk factors included young age, prematurity, history of atopy, exposure to tobacco smoke, underlying condition, neutrophilia, lymphopenia, and high CRP value. Conclusion: Children with viral coinfection, particularly with rhinovirus, RSV, influenza-A, PIV3, and bocavirus, may be followed closely regarding the clinical changes.