Clinical Characteristics Associated with Mortality in Children with Critically Ill Influenza B in the Pediatric Intensive Care Unit

Abstract

Purpose

Analysis of the clinical characteristics of critically ill children with influenza B.

Methods

This study is a retrospective study. It included 105 critically ill children with influenza B who were admitted to the Pediatric Intensive Care Unit (PICU) at the Children’s Hospital Affiliated with Zhengzhou University from January 2018 to December 2024. On the basis of their discharge outcomes, the patients were divided into a mortality group (n=11) and a survival group (n=94). We collected demographic and clinical data from the pediatric patients and compared the differences between the two groups.

Results

The mortality rate among 105 critically ill children with influenza B was 10.48%. The incidence of cough was lower in the group of children who died than in the group of children who survived, whereas the incidence of abdominal pain, altered consciousness, seizures, mechanical ventilation, and respiratory failure was higher in the group of children who died than in the group of children who survived. Children in the mortality group had significantly higher levels of D-dimer, aspartate aminotransferase, r-glutamyl transpeptidase, lactate dehydrogenase, procalcitonin, and interleukin-6 than those in the survival group did.

Conclusion

Children in the mortality group were older and had a lower incidence of cough than those in the survival group did. In the pediatric intensive care unit (PICU), characteristics associated with mortality in patients with influenza B include abdominal pain, altered consciousness, liver dysfunction, elevated inflammatory markers, or the need for mechanical ventilation. Children with influenza B admitted to the PICU often experience rapid disease progression and are prone to developing respiratory failure. Mechanical ventilation and respiratory failure are important clinical indicators of a severe deterioration in the condition of critically ill pediatric patients with influenza B in the PICU. Respiratory failure and circulatory failure are the direct causes of adverse outcomes in children in the mortality group.

Introduction

Influenza is an acute respiratory infectious disease caused by the influenza virus.¹ Influenza viruses are highly pathogenic and contagious RNA viruses classified into four types: A, B, C, and D. The subtypes circulating in the human population include influenza A (H1N1 and H3N2) and influenza B (Victoria lineage).¹ Influenza A and influenza B occur seasonally every year, and influenza A can cause global pandemics.² Previous epidemiological studies have shown that during the flu season, children under the age of 5 have the highest rate of influenza infection.^3,4 Although influenza is typically a mild, self-limiting illness, a small proportion of children with influenza may develop severe or critical cases because of complications such as pneumonia, acute respiratory distress syndrome (ARDS), encephalitis, acute necrotizing encephalopathy, and myocarditis or because of the exacerbation of underlying medical conditions.^3,5 These children typically require hospitalization and may even need to be transferred to a pediatric intensive care unit (PICU) for monitoring and advanced life support. Although flu-related deaths are rare, they do occur. Furthermore, according to a study by Jennifer Tam et al, more than half of all pediatric deaths from influenza occurred among children under the age of 5.⁶ Previous studies have also shown that children in this age group are prone to developing severe influenza.⁷ According to relevant research, influenza viruses cause 3 to 5 million cases of severe influenza and 650,000 deaths annually, with approximately 100,000 of these deaths occurring among children under the ages of 5 and 120,000 to 240,000 among adults over the age of 75.⁸

Currently, most related research focuses on influenza A, and reports on influenza B in children are rare. Furthermore, while previous studies generally reported that influenza A was more likely to lead to severe disease progression, recent research on influenza has shown that there is no significant difference between children with influenza B and those with influenza A in terms of length of stay in the PICU or clinical outcomes.⁹ Moreover, some studies suggest that influenza B is among the leading causes of flu-related deaths among children, and its infection rate is increasing annually.¹⁰ A study by Vishnu Arvindran Chandra Mohan et al found that influenza A is more frequently associated with neurological symptoms, while influenza B is associated with a higher prevalence of lower respiratory tract and gastrointestinal symptoms.¹¹ The treatment of critically ill children with influenza not only consumes a significant amount of PICU resources but also places tremendous physical, emotional, and financial burdens on their families. Currently, there are few studies analyzing risk factors associated with mortality in children with severe influenza B, leaving a significant knowledge gap. In this study, a retrospective analysis of 105 critically ill children with influenza B treated in the PICU was conducted. Clinical data were summarized and compared with the aim of providing guidance for predicting mortality risk in critically ill children with influenza and improving their prognosis.

Materials and Methods

Ethics Approval and Consent to Participate

This study was approved by the Ethics Committee of Henan Provincial Children’s Hospital (2024–131-001). Given that the study was retrospective, informed consent was not needed. The study adhered to the ethical standards of the Declaration of Helsinki.

Study Population

In this study, we included 105 critically ill children with influenza B who were hospitalized in the PICU at the Children’s Hospital Affiliated with Zhengzhou University from January 2018 to December 2024. The patients were divided into a survival group and a mortality group on the basis of their final clinical outcomes.

Inclusion and Exclusion Criteria

The diagnostic criteria for influenza B are defined as follows:¹² In accordance with the “Expert Consensus on the Diagnosis and Treatment of Influenza in Children (2020 Edition)”,¹³ a child is diagnosed with influenza B if they exhibit clinical symptoms of influenza—such as fever (body temperature ≥38°C) accompanied by cough or sore throat—and test positive for influenza B in one or more of the following pathogen tests: (1) a positive influenza B virus nucleic acid test and (2) a positive influenza B virus antigen test.

The diagnostic criteria for critically ill patients with influenza B are defined as follows:^12,13 patients who meet the diagnostic criteria for influenza B and who satisfy one of the following conditions: (1) respiratory failure; (2) acute necrotizing encephalopathy; (3) septic shock; (4) multiple organ dysfunction; and (5) other severe clinical conditions requiring intensive care.

The inclusion criteria were as follows: age greater than 1 month and less than 18 years; met the diagnostic criteria for critically ill patients with influenza B; and needed admission to the PICU during hospitalization because of clinical necessity.

The exclusion criteria were patients whose clinical data were incomplete or those who were transferred to another hospital for treatment during their hospitalization.

Grouping Criteria

Criteria for the survival group: Children who were discharged after their condition improved following active treatment.

The inclusion criteria for the mortality group were as follows: (1) death despite all resuscitation efforts due to an irreversible condition; and (2) extremely critical condition, a very poor prognosis on the basis of medical assessment, and inability to be weaned from respiratory or circulatory support (including ventilator-assisted ventilation and vasopressor support) at the time of discharge.

Data Collection

We retrospectively collected clinical data from 105 critically ill pediatric patients with influenza B who were admitted to the PICU; (1) baseline characteristics, such as gender, age in months, length of hospital stay, and presence of underlying conditions; (2) clinical manifestations, such as duration of fever and the presence of fever, cough, dyspnea, vomiting, abdominal pain, diarrhea, altered consciousness, and seizures; (3) chest CT findings, including the presence of pneumonia, pulmonary consolidation, pulmonary necrosis, atelectasis, and pleural effusion; (4) laboratory tests (within 24 hours before and after admission to the PICU, such as mixed infections, complete blood count, coagulation function, biochemical markers, immune function, and inflammatory markers); and (5) treatment measures, including whether mechanical ventilation was administered.

Statistical Analyses

We used SPSS software (version 26.0) for statistical analysis. Quantitative data that followed a normal distribution are presented as the mean ± standard deviation, and differences between groups were compared using an independent samples t test. Quantitative data that did not follow a normal distribution are expressed as the median P50 (P25, P75), and comparisons were performed using the Mann‒Whitney U-test. Qualitative data are expressed as percentages (%), and comparisons between groups were performed using the chi-square test or Fisher’s exact test. A two-sided P value < 0.05 indicated a statistically significant difference.

Results

Baseline Characteristics of Children with Critically Ill Influenza B

From January 2018 to December 2024, a total of 107 critically ill children with influenza B were admitted to our hospital’s PICU. Among them, 105 pediatric patients with critically ill influenza B patients met the inclusion and exclusion criteria; 94 (89.52%) were in the survival group, and 11 (10.48%) were in the mortality group. The median age of the children in the survival group was 16.50 (8.90, 40.50) months, the male-to-female ratio was 1.69:1, and the median length of stay in the PICU was 6.00 (3.00, 10.00) days. The median age of the children in the mortality group was 47.00 (18.00, 84.00) months, the male-to-female ratio was 1.75:1, and the median length of stay in the PICU was 7.00 (2.00, 12.00) days.

Comparison of Clinical Data Between the Two Groups of Pediatric Patients

There were no statistically significant differences between the two groups of pediatric patients in terms of gender, length of stay in the PICU, presence of underlying medical conditions, or presence of concurrent infections. The children in the survival group were significantly younger than those in the mortality group were. There were no statistically significant differences between the two groups of pediatric patients in terms of the number of days with fever or the prevalence of fever, vomiting, or diarrhea. The incidence of abdominal pain, altered consciousness, dyspnea, and seizures was significantly greater in the mortality group than in the survival group.

There were no statistically significant differences between the two groups of pediatric patients in terms of white blood cell count, red blood cell count, hemoglobin level, platelet count, percentage of neutrophils, percentage of lymphocytes, C-reactive protein (CRP) levels, or the presence of concurrent infections. The percentage of monocytes was significantly greater in the survival group than in the mortality group, and D-dimer levels were significantly lower in the survival group than in the mortality group. There were no statistically significant differences between the two groups of pediatric patients in terms of glutamic-pyruvic transaminase (ALT), total protein, globulin, immunoglobulin E (IgE), or erythrocyte sedimentation rate (ESR). Children in the survival group had significantly lower levels of glutamic oxaloacetic transaminase (AST), R-glutamyl transpeptidase, lactate dehydrogenase (LDH), procalcitonin (PCT), and interleukin-6 (IL-6) than those in the mortality group did, and higher albumin levels, with these differences being statistically significant. There was no statistically significant difference between the two groups of children regarding the use of antiviral medications within 48 hours of symptom onset. The proportion of children in the mortality group who required mechanical ventilation and experienced respiratory failure was significantly greater than that in the survival group, and this difference was statistically significant. There were no statistically significant differences between the two groups of pediatric patients in terms of pneumonia, pleural effusion, atelectasis, or pulmonary necrosis (Tables 1 and 2).

Table 1.

Comparison of Baseline Characteristics and Clinical Manifestations Between the Two Groups

	The Survival Group (n=94)	The Mortality Group (n=11)	P	95% CI
Gender Male	59,62.80%	7,63.60%	1.000	0.284–3.800
Age in months	16.5 (8.90,40.50)	47.00 (18.00,84.00)	0.023
Underlying conditions	27,28.70%	3,27.30%	1.000	0.229,3.774
Length of stay in the PICU	6.00 (3.00,10.00)	7.00 (2.00,12.00)	0.741
Number of days with fever	5.00 (2.00,10.00)	9.00 (5.00,12.00)	0.074
Fever	88,93.60%	11,100.00%	0.860	0.888,0.987
Cough	75,79.80%	5,45.50%	0.031	0.058,0.766
Dyspnea	27,28.70%	11,100.00%	<0.001	0.000,∞
Vomit	21,22.30%	5,45.50%	0.190	0.804,10.442
Diarrhea	6,6.40%	3,27.30%	0.076	11.152,26.266
Abdominal pain	7,7.40%	4,36.40%	0.015	1.666,30.272
Altered consciousness	24,25.50%	7,63.6%	0.023	1.373,18.975
Seizures	8,8.50%	5,45.50%	0.002	2.230,35.983

Table 2.

Comparison of Laboratory Test results and Imaging Findings Between the Two Groups

	The Survival Group (n=94)	The Mortality Group (n=11)	P	95% CI
WBC 10^9/L	7.94 (5.06,12.35)	9.18 (6.18,12.31)	0.320
RBC 10^12/L	4.00 (3.69,4.53)	4.05 (3.26,4.32)	0.352
HB g/L	108.00 (97.75,121.00)	105.00 (88.00,113.00)	0.405
PLT 10^9/L	311.00 (212.00,411.00)	256.00 (213.00,380.00)	0.383
Percentage of neutrophils	64.20 (46.30,77.85)	70.30 (50.30,86.40)	0.361
Percentage of lymphocytes	27.35 (17.43,45.95)	25.60 (12.50,43.90)	0.710
Percentage of monocytes	5.63±3.46	3.50±1.95	0.048	−4.244,-0.021
CRP mg/L	8.51 (2.93,30.84)	21.64 (3.77,99.96)	0.367
D-dimer ug/mL	0.44 (0.29,0.66)	2.60 (0.64,7.80)	0.001
ALT U/L	29.50 (21.40,47.45)	45.30 (24.20,162.50)	0.079
AST U/L	45.30 (33.00,57.35)	105.60 (49.00,138.00)	0.015
r-glutamyl transpeptidase U/L	19.80 (12.68,37.75)	32.40 (20.90,63.00)	0.042
Total protein g/L	62.31±8.89	62.26±11.95	0.989	−5.877,5.793
Albumin g/L	37.75 (30.90,42.63)	32.10 (29.70,35.40)	0.028
Globulin g/L	23.70 (21.08,28.05)	27.10 (21.50,35.00)	0.265
LDH U/L	329.20 (268.20,547.70)	583.20 (380.70,1162.60)	0.011
PCT ng/mL	0.23 (0.11,0.81)	1.05 (0.23,9.75)	0.012
IL-6 pg/mL	20.44 (7.46,42.21)	164.20 (23.18,733.95)	0.013
IgE IU/mL	43.09 (17.20,252.38)	54.51 (32.92,205.85)	0.713
ESR mm/h	12.00 (3.00,24.25)	31.00 (7.25,106.50)	0.058
Mechanical ventilation	51,54.30%	11,100.00%	0.009	0.000,∞
Use antiviral medications within 48 hours of the onset of symptoms	16,17.00%	1,9.10%	0.808	0.058,4.081
Concurrent infections	70,74.50%	7,63.60%	0.683	0.161,2.230
Respiratory failure	27,28.70%	11,100.00%	<0.001	0.000,∞
Pneumonia	82,87.20%	11, 100.00%	0.448	0.000,∞
Pulmonary consolidation	27,28.70%	2,18.20%	0.701	0.112,2.720
Pleural effusion	11,11.70%	2,18.20%	0.894	0.320,8.785
Atelectasis	2,2.10%	1,9.10%	0.722	0.382,55.348
Pulmonary necrosis	1,1.10%	0,0.00%	1.000	0.000,∞

Abbreviations: WBC, White blood cell count, RBC, red blood cell count, HB, hemoglobin, PLT, platelet count, CRP, C-reactive protein, ALT, glutamic-pyruvic transaminase, IgE, immunoglobulin E, ESR, erythrocyte sedimentation rate, AST, glutamic oxalacetic transaminase, LDH, lactate dehydrogenase, PCT, IL-6, procalcitonin, interleukin-6.

Discharge and Follow-Up Status in the Mortality Group

None of the children in the mortality group died in the hospital; all 11 were discharged in critical condition. Furthermore, it was not possible to follow up with these 11 children.

Underlying Conditions and Complications in the Mortality Group

Among the children in the mortality group, three had underlying medical conditions: one had congenital heart defects and a genetic metabolic disorder, one had a genetic metabolic disorder, and one had acute lymphoblastic leukemia. Among the children in the mortality group, 3 had ARDS, 5 had sepsis, and 3 had acute necrotizing encephalopathy.

Analysis of the Causes of Adverse Outcomes in Children in the Mortality Group

The mortality group in this study consisted of 11 pediatric patients, 9 of whom experienced adverse outcomes due to respiratory failure, which can be classified into two categories: peripheral respiratory failure and central respiratory failure. In four cases of peripheral respiratory failure, one child developed this condition because of the progression of severe pneumonia, resulting in an inability to maintain oxygen saturation; two children developed pneumothorax because of severe pulmonary lesions, leading to compression of lung tissue; and one child with acute lymphoblastic leukemia experienced pulmonary hemorrhage in addition to infection and bone marrow suppression, resulting in severe impairment of gas exchange. Five cases of central respiratory failure were reported: one child had acute necrotizing encephalopathy complicated by a brain herniation, leading to dysfunction of the respiratory center; two children had viral encephalitis and toxic encephalopathy, respectively, with involvement of the respiratory center, subsequently resulting in respiratory failure; one child had argininosuccinic aciduria, which experienced an acute exacerbation following an infection; and a sharp increase in blood ammonia levels stimulated the respiratory center, leading to respiratory failure. Two other pediatric patients experienced adverse outcomes due to respiratory and circulatory failure. One of these patients had severe pneumonia and septic shock, while the other had acute necrotizing encephalopathy with damage to the thalamus and brainstem, which led to neurogenic shock.

Discussion

Influenza viruses circulate worldwide and have a high mutation rate. Although influenza is a self-limiting disease, because children’s immune systems are not yet fully developed, some patients may develop severe or critically severe influenza, thereby increasing the risk of poor outcomes and death. Some studies suggest that influenza B is among the leading causes of hospitalization and death among children.¹⁴ The mortality rate among the pediatric patients with influenza B included in this study was 10.48%. Previous studies have estimated that the ratio of influenza A to influenza B cases during the same period was 9:1, but the case fatality rates were 19% and 10%, respectively.¹⁵ This is consistent with the findings of this study. Moreover, there was no statistically significant difference in gender distribution between the two groups of pediatric patients. In both groups of pediatric patients, males accounted for the majority. Studies have shown that prepubescent boys are more susceptible to severe seasonal influenza, which is consistent with the findings of this study.¹⁶ A study by Jacob Roved et al indicated that sex hormones are important regulators of the immune response; testosterone secreted by men typically has an immunosuppressive effect, whereas estrogen secreted by women has an immunostimulatory effect.¹⁷ However, there was no significant difference in sex hormone levels among children with influenza; therefore, this is likely not the reason why more boys than girls are affected. On the basis of previous studies, we speculate that this may be related to vaccination and social behavior.¹⁶

In this study, the median age of children with influenza B was 18.00 (9.85, 48.00) months. A serological study of children aged 0–7 years with influenza revealed that these children developed natural immunity to influenza B at a slower rate than to influenza A.¹⁵ In this study, the majority of children with influenza B were under 5 years of age, which is consistent with the findings of previous studies.^3,4 Moreover, our study revealed that the children in the mortality group were older than those in the survival group were. A previous study comparing the clinical characteristics and prevalence of influenza revealed that among children aged 14 and under, older children had a higher incidence of influenza B.¹⁸ Furthermore, compared with children under 6 months of age with influenza B, children aged 10 years and older have a greater risk of admission to the PICU.¹⁹ We speculate that this may be related to the immune system of older infants becoming more mature; an excessive immune response leads to a cytokine storm, which in turn causes damage to the body’s own tissues, such as ARDS and multiorgan dysfunction. In addition, older children sometimes exhibit less typical flu symptoms than infants and toddlers. This atypical presentation may lead parents to mistake the illness for a common cold, thereby delaying medical care.

Upon comparing the clinical manifestations of children in the mortality group with those in the survival group, we found that the proportion of children with cough was lower in the mortality group than in the survival group. This may be related to the fact that the children in the mortality group were in critical condition and had significantly weakened or absent cough reflexes. From a pathophysiological perspective, coughing is an important defense mechanism of the respiratory tract; an effective cough helps clear pathogens and secretions, thereby reducing the risk of worsening lung infections.²⁰ Moreover, the impact of clinical interventions cannot be ruled out; children with prominent coughs may have received airway care and antimicrobial therapy earlier, thereby improving the course of the disease. In addition, a weakened cough reflex may also be associated with central nervous system suppression, severe muscle fatigue, or sedation. These findings suggest that in the PICU, early intervention should be implemented for critically ill pediatric influenza patients who cough infrequently to reduce the risk of their condition worsening. In this study, a greater proportion of children in the mortality group experienced abdominal pain during the course of their illness than did those in the survival group did. These findings suggest that gastrointestinal dysfunction in critically ill children with influenza B may be associated with poor prognosis, but further research is needed to verify these findings. The incidence of altered consciousness and seizures was higher in the mortality group than in the survival group. These findings suggest that when the nervous system is affected in critically ill children with influenza B, this condition is often associated with poor prognosis. A study by Raffaele Vitale et al indicated that neurological involvement in children with influenza is caused primarily by systemic immune dysregulation—including cytokine storms and endothelial damage—rather than direct viral invasion of the nervous system.²¹

In this study, D-dimer levels were higher in the mortality group than in the survival group. D-dimer is produced by the breakdown of fibrin under the action of fibrinolysin, indicating the dual activation of the coagulation and fibrinolytic systems. Previous animal studies have shown that influenza virus infection enhances coagulation by increasing thrombin production and fibrin deposition.²² Wang Siqi et al reported that D-dimer levels are an independent risk factor for critically ill patients with influenza.²³ Previous studies have also shown that patients with severe influenza exhibit coagulation abnormalities, such as elevated D-dimer levels.²³ This is consistent with the findings of this study. Moreover, relevant studies have shown that the immune response in patients with severe influenza is exacerbated by abnormal coagulation, including pulmonary endothelial activation, vascular leakage, disseminated intravascular coagulation, and pulmonary microvascular thrombosis.²² An excessive immune inflammatory response may lead to acute lung injury, ARDS, and other conditions, thereby affecting a child’s prognosis.

In this study, AST levels were higher in the mortality group than in the survival group. Both groups of pediatric patients exhibited impaired liver function. Moreover, the same time, albumin levels in the mortality group were lower than those in the survival group. Previous studies have shown that influenza viruses may cause direct damage to the liver or indirectly damage liver tissue through immune-mediated mechanisms.²⁴ These findings suggest that liver damage in pediatric patients with influenza B in the PICU may be associated with severe disease progression. Since impaired liver function leads to impaired synthesis of albumin and coagulation factors, decreased albumin levels and coagulation disorders may also be associated with poor prognosis.

In our study, the levels of inflammatory markers such as LDH, PCT, and IL-6 were higher in the mortality group than in the survival group. A study by Gabriel Laghlali et al suggested that severe influenza infection may be associated with excessive inflammatory responses and damage to the lung epithelium.²⁵ In severe cases of influenza infection, the virus may invade the lower respiratory tract, infect lung epithelial cells, and thereby promote an inflammatory response and the activation of apoptosis pathways.²⁵ Moreover, studies have indicated that severe influenza infection may trigger a cytokine storm, which can damage lung epithelial cells; in severe cases, this can even lead to multiple organ failure, thereby increasing the mortality rate.²⁵

Previous studies have shown that approximately 60% of patients admitted to intensive care units due to respiratory complications resulting from influenza infection require mechanical ventilation.²⁶ In our study, the proportion of children on mechanical ventilation was greater in the mortality group than in the survival group. Children requiring mechanical ventilation often indicate a more severe clinical deterioration. We speculate that this discrepancy may stem from two factors: First, pediatric influenza patients requiring mechanical ventilation typically have more severe conditions, resulting in poorer outcomes; second, studies have indicated that mechanical ventilation itself may exacerbate existing lung injury or even induce new lung injury, thereby leading to poor prognosis.²⁶

In this study, all 11 children in the mortality group had respiratory failure, and 3 of them also had ARDS. Previous studies have shown that children with influenza complicated by ARDS have a higher mortality rate.^27,28 A retrospective study revealed that patients who died from ARDS due to influenza virus infection exhibited delayed clearance of the virus from the nasopharynx, higher levels of pro-inflammatory cytokines and chemokines, and a greater likelihood of developing viremia.²⁹ These findings suggest that influenza-induced ARDS may be related to either direct viral damage or the host’s immune response to the virus.²⁹ Acute necrotizing encephalopathy is another cause of death among children with influenza.²⁹ It is characterized primarily by rapid deterioration of the nervous system, which may leads to a poor prognosis.³⁰ In this study, 27.27% of the children in the mortality group had acute necrotizing encephalopathy. According to the latest report from the U.S. Centers for Disease Control and Prevention, acute necrotizing encephalopathy accounts for 9% of influenza-related deaths among children in the United States.³¹ This condition is difficult to diagnose in its early stages, and no targeted, effective treatments are available. Once impaired consciousness occurs, the rapid progression of the disease may result in a missed window of opportunity for emergency intervention. In this study, 45.45% of the children in the mortality group also had sepsis. On the one hand, influenza viruses damage the mucosal barrier of the respiratory tract, creating conditions conducive to secondary bacterial infections. On the other hand, the cytokine storm induced by the virus can lead to uncontrolled systemic inflammation, causing damage to the vascular endothelium, microcirculatory dysfunction, and multi-organ dysfunction, which in turn leads to the development of sepsis. Sepsis itself can lead to hemodynamic instability, inadequate tissue perfusion, and the development of ARDS, which in turn can result in a poor prognosis.

In this study, all 11 children in the mortality group experienced adverse clinical outcomes due to respiratory failure. Two of the pediatric patients were unable to maintain both respiratory and circulatory functions. Overall, severe dysfunction of the respiratory and circulatory systems, which are intertwined and exacerbate one another, is a key factor contributing to poor treatment outcomes.

This study is a single-center retrospective study and has certain limitations. Due to the small number of cases in the mortality group and the lack of multivariate adjustment, confounding bias may be present; therefore, differences between groups should not be interpreted as independent predictive factors but should only be considered as indicative of potential associations. The conclusions require further validation through large-scale, multicenter cohort studies. Additionally, we did not analyze differences in clinical characteristics among different lineages of influenza B; further research is needed to explore these issues.

In summary, our study revealed that the mortality rate among children with critically ill influenza B was 10.48%, and both groups consisted predominantly of male children. Children in the mortality group were older and had a lower incidence of cough than those in the survival group did. Among critically ill children with influenza B in the PICU, abdominal pain, altered mental status, liver dysfunction, elevated inflammatory markers, and mechanical ventilation were clinical features associated with mortality in this cohort. Furthermore, pediatric patients with influenza admitted to the PICU often experience rapid disease progression and are prone to developing respiratory failure; some may develop ARDS or acute necrotizing encephalopathy, thereby increasing the risk of death. Children who require mechanical ventilation and develop respiratory failure often indicate a more severe clinical deterioration.

Funding Statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data Sharing Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Ethics Approval and Consent to Participate

This study was approved by the Ethics Committee of Henan Provincial Children’s Hospital (2024-131-001). Given that the study was retrospective, informed consent was not needed. The Ethics Committee has approved the waiver of informed consent. The study adhered to the ethical standards of the Declaration of Helsinki.

Consent for Publication

All data from this study were released with the consent of the children’s parents.

Disclosure

The authors declare that they have no competing interests.