Risk factors in pediatric hospitalization for influenza A and B during the seven seasons immediately before the COVID-19 era in Japan.

INTRODUCTION: The risk factors in pediatric influenza immediately before the COVID-19 era are not well understood. This study aims to evaluate the risk factors for hospitalization in pediatric influenza A and B for the recent seasons. METHODS: Children with a fever of ≥38 °C and laboratory-confirmed influenza at 20 hospitals in outpatient settings in Japan in the 2013/14 to 2019/20 seasons were retrospectively reviewed. Possible risk factors, including gender, age, comorbidities, nursery school or kindergarten attendance, earlier diagnosis, no immunization, lower regional temperature, earlier season, and period of onset, were evaluated using binary logistic regression methods. RESULTS: A total of 13,040 (type A, 8861; B, 4179) children were evaluated. Significant risk factors (p < 0.05) in multivariate analyses were young age, lower regional temperature, earlier season, respiratory illness (adjusted odds ratio [aOR]:2.76, 95% confidence interval [CI]:1.84-4.13), abnormal behavior and/or unusual speech (aOR:2.78, 95% CI:1.61-4.80), and seizures at onset (aOR:16.8, 95% CI:12.1-23.3) for influenza A; and young age, lower regional temperature, respiratory illness (aOR:1.99, 95% CI:1.00-3.95), history of febrile seizures (aOR:1.73, 95% CI:1.01-2.99), and seizures at onset (aOR:9.74, 95% CI:5.44-17.4) for influenza B. CONCLUSIONS: In addition to previously known factors, including young age, seizures, and respiratory illness, abnormal behavior and/or unusual speech and lower regional temperature are new factors. Negative immunization status was not a risk factor for hospitalization. A better understanding of risk factors may help improve the determination of indications for hospitalization during the future co-circulation of influenza and COVID-19.

Exogenous remodeling of lung resident macrophages protects against infectious consequences of bone marrow-suppressive chemotherapy.

Infection is the single greatest threat to survival during cancer chemotherapy because of depletion of bone marrow-derived immune cells. Phagocytes, especially neutrophils, are key effectors in immunity to extracellular pathogens, which has limited the development of new approaches to protect patients with cancer and chemotherapy-induced neutropenia. Using a model of vaccine-induced protection against lethal Pseudomonas aeruginosa pneumonia in the setting of chemotherapy-induced neutropenia, we found a population of resident lung macrophages in the immunized lung that mediated protection in the absence of neutrophils, bone marrow-derived monocytes, or antibodies. These vaccine-induced macrophages (ViMs) expanded after immunization, locally proliferated, and were closely related to alveolar macrophages (AMs) by surface phenotype and gene expression profiles. By contrast to AMs, numbers of ViMs were stable through chemotherapy, showed enhanced phagocytic activity, and prolonged survival of neutropenic mice from lethal P. aeruginosa pneumonia upon intratracheal adoptive transfer. Thus, induction of ViMs by tissue macrophage remodeling may become a framework for new strategies to activate immune-mediated reserves against infection in immunocompromised hosts.

Pore-Forming Toxins Induce Macrophage Necroptosis during Acute Bacterial Pneumonia.

Necroptosis is a highly pro-inflammatory mode of cell death regulated by RIP (or RIPK)1 and RIP3 kinases and mediated by the effector MLKL. We report that diverse bacterial pathogens that produce a pore-forming toxin (PFT) induce necroptosis of macrophages and this can be blocked for protection against Serratia marcescens hemorrhagic pneumonia. Following challenge with S. marcescens, Staphylococcus aureus, Streptococcus pneumoniae, Listeria monocytogenes, uropathogenic Escherichia coli (UPEC), and purified recombinant pneumolysin, macrophages pretreated with inhibitors of RIP1, RIP3, and MLKL were protected against death. Alveolar macrophages in MLKL KO mice were also protected during S. marcescens pneumonia. Inhibition of caspases had no impact on macrophage death and caspase-1 and -3/7 were determined to be inactive following challenge despite the detection of IL-1ß in supernatants. Bone marrow-derived macrophages from RIP3 KO, but not caspase-1/11 KO or caspase-3 KO mice, were resistant to PFT-induced death. We explored the mechanisms for PFT-induced necroptosis and determined that loss of ion homeostasis at the plasma membrane, mitochondrial damage, ATP depletion, and the generation of reactive oxygen species were together responsible. Treatment of mice with necrostatin-5, an inhibitor of RIP1; GW806742X, an inhibitor of MLKL; and necrostatin-5 along with co-enzyme Q10 (N5/C10), which enhances ATP production; reduced the severity of S. marcescens pneumonia in a mouse intratracheal challenge model. N5/C10 protected alveolar macrophages, reduced bacterial burden, and lessened hemorrhage in the lungs. We conclude that necroptosis is the major cell death pathway evoked by PFTs in macrophages and the necroptosis pathway can be targeted for disease intervention.

Collaboration between macrophages and vaccine-induced CD4+ T cells confers protection against lethal Pseudomonas aeruginosa pneumonia during neutropenia.

The usefulness of vaccine-based strategies to prevent lethal bacterial infection in a host with neutropenia is not well-defined. Here, we show in a neutropenic mouse model that immunity induced by mucosal vaccination with a live-attenuated Pseudomonas aeruginosa vaccine is protective against lethal P. aeruginosa pneumonia caused by both vaccine-homologous and vaccine-heterologous strains, whereas passive immunization confers only vaccine-homologous protection. Cells in the macrophage lineage served as crucial innate cellular effectors in the neutropenic host after active immunization. Vaccine efficacy was CD4(+) T-cell dependent and associated with accumulation of macrophage-lineage cells in the alveolar space after infection, as well as with enhanced P. aeruginosa clearance from the lung. Adaptive CD4(+) T cells produced granulocyte-macrophage colony-stimulating factor (GM-CSF) on restimulation in vitro, and local GM-CSF was critical for vaccine efficacy. Thus, collaboration between the innate and adaptive effectors induced by mucosal vaccination can overcome neutropenia and confer protection against lethal bacterial infection in the profoundly neutropenic host.

Effectiveness of inactivated influenza vaccine in children during the 2023/24 season: The first season after relaxation of intensive COVID-19 measures.

BACKGROUND: The annual administration of the influenza vaccine is the most effective method for preventing influenza. We have evaluated the effectiveness of the inactivated influenza vaccine in children aged 6 months to 15 years across the seasons from 2013/2014 to 2022/2023. This study aims to investigate the effectiveness of the inactivated influenza vaccine in the 2023/2024 season, the first year following the easing of strict COVID-19 measures, and possibly the last season when only the inactivated vaccine is available on the market. METHODS: Adjusted vaccine effectiveness for the 2023/2024 season was assessed using a test-negative case-control design, with results based on polymerase chain reaction and rapid influenza diagnostic tests. Vaccine effectiveness was calculated by influenza type and patient hospitalization/outpatient status. RESULTS: A total of 1832 children were recruited. The inactivated influenza vaccine was effective in preventing both symptomatic influenza A and B in both inpatient and outpatient settings. Overall vaccine effectiveness for influenza A was 51% (95% confidence interval [CI], 23%-69%, n = 930) in inpatient settings and 54% (95%CI, 27%-71%, n = 559) in outpatient settings. For influenza B, effectiveness was 60% (95%CI, 22%-79%, n = 859) in inpatient settings and 56% (95%CI, 26%-74%, n = 558) in outpatient settings. Analysis suggested that administering two doses enhanced effectiveness specifically against influenza B. CONCLUSIONS: This is the first study to demonstrate influenza vaccine effectiveness in children after the relaxation of strict COVID-19 measures in Japan (2023/2024). We recommend the current inactivated vaccine for preventing both influenza A and B in children, with consideration for the potential use of two doses to enhance effectiveness against influenza B.

Mucosal vaccination with a multivalent, live-attenuated vaccine induces multifactorial immunity against Pseudomonas aeruginosa acute lung infection.

Many animal studies investigating adaptive immune effectors important for protection against Pseudomonas aeruginosa have implicated opsonic antibody to the antigenically variable lipopolysaccharide (LPS) O antigens as a primary effector. However, active and passive vaccination of humans against these antigens has not shown clinical efficacy. We hypothesized that optimal immunity would require inducing multiple immune effectors targeting multiple bacterial antigens. Therefore, we evaluated a multivalent live-attenuated mucosal vaccination strategy in a murine model of acute P. aeruginosa pneumonia to assess the contributions to protective efficacy of various bacterial antigens and host immune effectors. Vaccines combining 3 or 4 attenuated strains having different LPS serogroups were associated with the highest protective efficacy compared to vaccines with fewer components. Levels of opsonophagocytic antibodies, which were directed not only to the LPS O antigens but also to the LPS core and surface proteins, correlated with protective immunity. The multivalent live-attenuated vaccines overcame prior problems involving immunologic interference in the development of O-antigen-specific antibody responses when closely related O antigens were combined in multivalent vaccines. Antibodies to the LPS core were associated with in vitro killing and in vivo protection against strains with O antigens not expressed by the vaccine strains, whereas antibodies to the LPS core and surface proteins augmented the contribution of O-antigen-specific antibodies elicited by vaccine strains containing a homologous O antigen. Local CD4 T cells in the lung also contributed to vaccine-based protection when opsonophagocytic antibodies to the challenge strain were absent. Thus, multivalent live-attenuated vaccines elicit multifactorial protective immunity to P. aeruginosa lung infections.

Analysis of acquisition of Pseudomonas aeruginosa gastrointestinal mucosal colonization and horizontal transmission in a murine model.

BACKGROUND: Laboratory systems to study bacterial transmission and mucosal colonization leading to infection have not been utilized. METHODS: We determined whether transmission of various strains of Pseudomonas aeruginosa among individual mice could occur and investigated the properties of such strains in establishing gastrointestinal (GI) mucosal colonization as well as in disseminating systemically after induction of neutropenia. RESULTS: P. aeruginosa isolates associated with epidemic spread among patients with cystic fibrosis (CF) readily established GI colonization at higher levels than did strains associated with acute infections in patients without CF, and they outcompeted these strains. Colonization was associated with resistance to bile salts. However, epidemic CF isolates did not disseminate after induction of neutropenia and did not induce as much mucosal pathology as did strains that were capable of disseminating. CONCLUSION: Murine models can be used to study P. aeruginosa transmission and early colonization, and the properties of these strains associated with their known clinical behaviors are mimicked in this setting.

Influenza vaccine effectiveness against influenza A in children based on the results of various rapid influenza tests in the 2018/19 season.

During influenza epidemics, Japanese clinicians routinely conduct rapid influenza diagnostic tests (RIDTs) in patients with influenza-like illness, and patients with positive test results are treated with anti-influenza drugs within 48 h after the onset of illness. We assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children (6 months-15 years old, N = 4243), using a test-negative case-control design based on the results of RIDTs in the 2018/19 season. The VE against influenza A(H1N1)pdm and A(H3N2) was analyzed separately using an RIDT kit specifically for detecting A(H1N1)pdm09. The adjusted VE against combined influenza A (H1N1pdm and H3N2) and against A(H1N1)pdm09 was 39% (95% confidence interval [CI], 30%-46%) and 74% (95% CI, 39%-89%), respectively. By contrast, the VE against non-A(H1N1)pdm09 influenza A (presumed to be H3N2) was very low at 7%. The adjusted VE for preventing hospitalization was 56% (95% CI, 16%-77%) against influenza A. The VE against A(H1N1)pdm09 was consistently high in our studies. By contrast, the VE against A(H3N2) was low not only in adults but also in children in the 2018/19 season.

IL-17 is a critical component of vaccine-induced protection against lung infection by lipopolysaccharide-heterologous strains of Pseudomonas aeruginosa.

In a murine model of acute fatal pneumonia, we previously showed that nasal immunization with a live-attenuated aroA deletant of Pseudomonas aeruginosa strain PAO1 elicited LPS serogroup-specific protection, indicating that opsonic Ab to the LPS O Ag was the most important immune effector. Because P. aeruginosa strain PA14 possesses additional virulence factors, we hypothesized that a live-attenuated vaccine based on PA14 might elicit a broader array of immune effectors. Thus, an aroA deletant of PA14, denoted PA14DeltaaroA, was constructed. PA14DeltaaroA-immunized mice were protected against lethal pneumonia caused not only by the parental strain but also by cytotoxic variants of the O Ag-heterologous P. aeruginosa strains PAO1 and PAO6a,d. Remarkably, serum from PA14DeltaaroA-immunized mice had very low levels of opsonic activity against strain PAO1 and could not passively transfer protection, suggesting that an antibody-independent mechanism was needed for the observed cross-serogroup protection. Compared with control mice, PA14DeltaaroA-immunized mice had more rapid recruitment of neutrophils to the airways early after challenge. T cells isolated from P. aeruginosa DeltaaroA-immunized mice proliferated and produced IL-17 in high quantities after coculture with gentamicin-killed P. aeruginosa. Six hours following challenge, PA14DeltaaroA-immunized mice had significantly higher levels of IL-17 in bronchoalveolar lavage fluid compared with unimmunized, Escherichia coli-immunized, or PAO1DeltaaroA-immunized mice. Antibody-mediated depletion of IL-17 before challenge or absence of the IL-17 receptor abrogated the PA14DeltaaroA vaccine's protection against lethal pneumonia. These data show that IL-17 plays a critical role in antibody-independent vaccine-induced protection against LPS-heterologous strains of P. aeruginosa in the lung.

Utility of in vivo transcription profiling for identifying Pseudomonas aeruginosa genes needed for gastrointestinal colonization and dissemination.

Microarray analysis of Pseudomonas aeruginosa mRNA transcripts expressed in vivo during animal infection has not been previously used to investigate potential virulence factors needed in this setting. We compared mRNA expression in bacterial cells recovered from the gastrointestinal (GI) tracts of P. aeruginosa-colonized mice to that of P. aeruginosa in the drinking water used to colonize the mice. Genes associated with biofilm formation and type III secretion (T3SS) had markedly increased expression in the GI tract. A non-redundant transposon library in P. aeruginosa strain PA14 was used to test mutants in genes identified as having increased transcription during in vivo colonization. All of the Tn-library mutants in biofilm-associated genes had an attenuated ability to form biofilms in vitro, but there were no significant differences in GI colonization and dissemination between these mutants and WT P. aeruginosa PA14. To evaluate T3SS factors, we tested GI colonization and neutropenia-induced dissemination of both deletional (PAO1 and PAK) and insertional (PA14) mutants in four genes in the P. aeruginosa T3SS, exoS or exoU, exoT, and popB. There were no significant differences in GI colonization among these mutant strains and their WT counterparts, whereas rates of survival following dissemination were significantly decreased in mice infected by the T3SS mutant strains. However, there was a variable, strain-dependent effect on overall survival between parental and T3SS mutants. Thus, increased transcription of genes during in vivo murine GI colonization is not predictive of an essential role for the gene product in either colonization or overall survival following induction of neutropenia.

C1q nephropathy in a 2-year-old boy presenting with steroid resistant nephrotic syndrome.

We experienced a case of a 2-year-old boy, who presented with steroid resistant nephrotic syndrome, which developed insidiously. Renal biopsy revealed that he had focal and segmental glomerulosclerosis on light microscopy, dominant mesangial deposition of C1q by immunofluorescent staining, and electron dense deposits on electron microscopy, which are all compatible with C1q nephropathy. He had no clinical sign of any collagen diseases, including systemic lupus erythematodes. So, the diagnosis of C1q nephropathy was made. An intensive treatment by a combination of cyclosporine, prednisolone and methylprednisolone pulse therapy was successful in achieving remission and disappearance of proteinuria in this patient. Although he developed hypertension requiring calcium blocker and angiotensin converting enzyme inhibitor, his renal function stayed within normal limit for 3 years after the initiation of the treatment. The growth was well preserved during the 3 years of treatment with almost unchanged SD scores for height. He has delay in speech, which may not be associated with the etiology of his nephropathy, based on the absence of such association in the previous reports. C1q nephropathy is still a controversial clinical entity, so accumulation of the cases may help further understand the pathogenesis and clinical manifestation of C1q nephropathy.