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Mycoplasma pneumoniae infections declined sharply during COVID-19 non-pharmaceutical interventions but have resurged in multiple regions after restrictions were lifted. This narrative Perspective synthesizes recent epidemiologic and molecular observations and emphasizes children as a key reservoir sustaining community transmission. We highlight how asymptomatic carriage and prolonged upper-airway detection complicate interpretation of PCR results, and we discuss the clinical implications of macrolide-resistant M. pneumoniae (MRMP), including pragmatic, age-stratified management considerations. Finally, we outline priorities for surveillance and for translating genomic signals into simplified clinical pathways, particularly in high-MRMP settings.

Mycoplasma pneumoniae (Mp) is one of the leading causes of community‐acquired pneumonia and can cause a number of extrapulmonary manifestations in the absence of pneumonia. In this regard, primary care physicians should know how to suspect, diagnose, and manage patients with Mp infection. This review gives a general overview of the basic clinical aspects of Mp infection with special reference to pneumonia, which will help further understanding of the disease.

Background: Idiopathic pulmonary fibrosis (IPF) is the most common and severe form of idiopathic interstitial pneumonia, and its prevalence increases with age. In the era of pre-antifibrotic agents, the median survival time of Japanese patients with IPF is 35 months, with a 5-year survival rate in western countries ranging from 20% to 40%. The prevalence of IPF is highest in elderly patients aged ≥75 years; however, the efficacy and safety of long-term use of pirfenidone and/or nintedanib are not fully understood. Objective: This study aimed to determine the efficacy and safety of the sole use of antifibrotic agents (pirfenidone or nintendanib) for IPF in the elderly. Method: We retrospectively reviewed patients with IPF who were diagnosed and treated with either pirfenidone or nintedanib in our hospital between 2008 and 2019. We excluded patients with the subsequent use of both antifibrotic agents. We examined the survival probability and frequency of acute exacerbation, with focus on long-term use (≥1 year), elderly patients (≥75 years of age), and disease severity. Results: We identified 91 patients with IPF (male to female ratio: 63 to 28, age 42 to 90 years). The numbers of patients with disease severity classified by JRS (I/II/III/IV) and GAP stage (I/II/III) were (38/6/17/20) and (39/36/6), respectively. The survival probabilities were comparable between the elderly (n = 46) and non-elderly groups (n = 45, p = 0.877). After the initiation of antifibrotic agents, the cumulative incidence ratio of acute exacerbation of IPF was significantly lower in the early stage (GAP stage I, n = 20) than in the progressive stage of disease (GAP stages II and III, n = 20, p = 0.028). A similar trend was noted in the JRS disease severity classification (I, II vs. III, IV) (n = 27 vs. n = 13, p = 0.072). In the long-term treatment (≥1 year) group (n = 40), the survival probabilities at 2 and 5 years after treatment initiation were 89.0% and 52.4%, respectively, which did not reach the median survival rate. Conclusions: Even in elderly patients (≥75 years of age), antifibrotic agents demonstrated positive effects on survival probability and the frequency of acute exacerbation. These positive effects would be improved for earlier JRS/GAP stages or long-term use.

Background Increased pleural fluid adenosine deaminase (ADA) is useful for diagnosing tuberculous pleurisy (TB), but high ADA levels are associated with other diseases. In this study, we compare various disease characteristics in patients with high-ADA pleural effusion. Methods We retrospectively collected data for 456 patients with pleural fluid ADA levels of ≥ 40 U/L from January 2012 to October 2021. Cases were classified as TB (n = 203), pleural infection (n = 112), malignant pleural effusion (n = 63), nontuberculous mycobacteria (n = 22), malignant lymphoma (ML) (n = 18), autoimmune diseases (n = 11), and other diseases (n = 27), and data were compared among those diseases. Predictive factors were identified by comparing data for a target disease to those for all other diseases. A diagnostic flowchart for TB was developed based on those factors. Results The most frequent disease was TB, though 60.0% of patients were diagnosed with other diseases. Median ADA levels in patients with TB were 83.1 U/L (interquartile range [IQR] 67.2–104.1), higher than those of patients with pleural infection (median 60.9 [IQR 45.3–108.0], p  = 0.004), malignant pleural effusion (median 54.1 [IQR 44.8–66.7], p  < 0.001), or autoimmune diseases (median 48.5 [IQR 45.9–58.2], p  = 0.008), with no significant difference from NTM ( p  = 1.000) or ML ( p  = 1.000). Pleural fluid lactate dehydrogenase (LDH) levels of < 825 IU/L were beneficial for the diagnosis of TB. Neutrophil predominance or cell degeneration, white blood cell count of ≥ 9200/µL or C-reactive protein levels of ≥ 12 mg/dL helped in diagnosing pleural infection. Pleural fluid amylase levels of ≥ 75 U/L and a pleural fluid ADA/total protein (TP) ratio of < 14 helped in diagnosing malignant pleural effusion. High serum LDH and high serum/pleural fluid eosinophils helped in diagnosing ML and autoimmune diseases, respectively. The flowchart was comprised of the following three factors: pleural fluid LDH < 825 IU/L, pleural fluid ADA/TP of < 14, and neutrophil predominance or cell degeneration, which were decided by a decision tree. The diagnostic accuracy rate, sensitivity, and specificity for the diagnosis of TB were 80.9%, 78.8%, and 82.6%, respectively. Conclusion Cases involving high pleural fluid ADA levels should be investigated using several factors to distinguish TB from other diseases.

In pulmonary sarcoidosis, alveolar macrophages (AMs) undergo epithelioid transformation, but their quantitative morphologic characteristics and association with systemic disease markers remain incompletely defined. Do enlargement and activation features of AMs in bronchoalveolar lavage (BAL) samples correlate with systemic markers of sarcoidosis activity (ACE and sIL-2R)? BAL cells from 16 biopsy-confirmed sarcoidosis cases and 4 healthy controls were cytocentrifuged, Diff-Quik®-stained, and analyzed using a digital planimetric microscope. Cell area (CA) of 50 randomly selected AMs per subject (total = 1,000) was quantified and categorized as small, medium, large, or extra-large based on control mean ± SD cutoffs. Nonparametric tests and principal component analysis (PCA) were applied to examine associations among CA, morphological features, serum ACE, and sIL-2R. The mean CA was 31% greater in sarcoidosis than in controls (368.2 ± 169.3 μm vs. 281.4 ± 90.9 μm ;  < 0.001), with higher proportions of large/extra-large AMs (41% vs. 14%;  < 0.001). Vacuolation, rosette formation, and membrane ruffling were hallmarks of AM activation, correlating strongly with serum ACE and sIL-2R but not with the BALF CD4/CD8 ratio. AM enlargement and activation features are quantitative, reproducible surrogates of disease activity in pulmonary sarcoidosis. Clinical implications: Quantitative assessment of alveolar macrophage morphology may aid in assessment and monitoring of sarcoidosis activity and treatment response.

Human metapneumovirus genotype B (HMPV-B) is an important respiratory pathogen, requiring detailed elucidation of the evolutionary and antigenic features of its fusion (F) gene. Using 500 sequences collected between 1982 and 2024, we investigated the molecular evolution, phylodynamics, and structural epitope landscape of the HMPV-B F gene. Time-scaled phylogeny dated the divergence of sublineages B1 and B2 to around 1937, and Bayesian Skyline Plot analysis showed that these sublineages exhibited distinct demographic trajectories over time. The F gene evolved at a rate of 1.01 × 10−3 substitutions/site/year; however, amino acid variation remained limited, consistent with pervasive purifying selection, with 39% of codons under strong negative selection and little consensus evidence for positive selection. Conformational B-cell epitope prediction demonstrated a high degree of conservation across neutralizing antibody binding regions (sites Ø and I–V), and amino acid substitutions occurring within these sites were not predicted to substantially alter epitope architecture. Together, these findings indicate that the HMPV-B F gene evolves under strong evolutionary constraint while maintaining stable antigenic features, supporting the potential for antibody-based strategies that target neutralizing antibody binding regions of the F protein.

Background Neutrophilic inflammation is associated with poorly controlled asthma. Serum levels of sST2, a soluble IL-33 receptor, increase in neutrophilic lung diseases. We hypothesized that high serum sST2 levels in stable asthmatics are a predictor for exacerbation within a short duration. Methods This prospective observational study evaluated the serum sST2 levels of 104 asthmatic patients who were treated by a lung disease specialist with follow-ups for 3 months. Results High serum sST2 levels (> 18 ng/ml) predicted severe asthma exacerbation within 3 months. Serum sST2 levels correlated positively with asthma severity (treatment step), airway H 2 O 2 levels, and serum IL-8 levels. High serum sST2 levels and blood neutrophilia (> 6000 /μl) were independent predictors of exacerbation. We defined a post-hoc exacerbation-risk score combining high serum sST2 level and blood neutrophilia, which stratified patients into four groups. The score predicted exacerbation-risk with an area under curve of 0.91 in the receiver operating characteristic curve analysis. Patients with the highest scores had the most severe phenotype, with 85.7% showing exacerbation, airflow limitation, and corticosteroid-insensitivity. Conclusions High serum sST2 levels predicted exacerbation within the general asthmatic population and, when combined with blood neutrophil levels, provided an exacerbation-risk score that was an accurate predictor of exacerbation occurring within 3 months.

BackgroundSome patients with idiopathic interstitial pneumonia (IIP) show autoimmune features. Interstitial pneumonia with autoimmune features (IPAF) was recently proposed as a research concept in these patients. However, retrospective studies reported conflicting results of its prognosis. Therefore, this study was conducted to prospectively evaluate the clinical significance of autoimmune features in patients with IIP.MethodsThis nationwide multicentre study prospectively enrolled consecutive patients with IIP. At the diagnosis, we systematically evaluated 63 features suggestive of connective tissue diseases using a checklist including symptoms/signs and autoantibodies, which contained most items of the IPAF criteria and followed up with the patients. Clinical phenotypes were included in a cluster analysis.ResultsIn 376 patients with IIP enrolled, 70 patients (18.6%) met the IPAF criteria. The proportion of patients with IPAF was significantly lower in idiopathic pulmonary fibrosis (IPF) than in non-IPF (6.0% vs 24.3%, respectively). During a median observation period of 35 months, patients with IPAF more frequently developed systemic autoimmune diseases and had less frequent acute exacerbation of IIPs than patients with non-IPAF. IPAF diagnosis was significantly associated with better survival and was an independent positive prognostic factor in total and patients with non-IPF. Cluster analysis by similarity of clinical phenotypes identified a cluster in which there was a higher number of women, and patients had more autoimmune features and a better prognosis than other clusters.InterpretationThese observations suggest that some patients with IIP show autoimmune features with distinct characteristics and favourable prognosis. However, we were not able to determine the appropriate therapies for these patients.

There are currently no antiviral agents for human metapneumovirus (HMPV), respiratory syncytial virus (RSV), mumps virus (MuV), or measles virus (MeV). Favipiravir has been developed as an anti-influenza agent, and this agent may be effective against these viruses in vitro. However, the molecular mechanisms through which the agent affects virus replication remain to be fully elucidated. Thus, to clarify the detailed molecular interactions between favipiravir and the RNA-dependent RNA polymerase (RdRp) of HMPV, RSV, MuV, MeV, and influenza virus, we performed in silico studies using authentic bioinformatics technologies. As a result, we found that the active form of favipiravir (favipiravir ribofuranosyl-5′-triphosphate [F-RTP]) can bind to the RdRp active sites of HMPV, RSV, MuV, and MeV. The aspartic acid residue of RdRp active sites was involved in the interaction. Moreover, F-RTP was incorporated into the growing viral RNA chain in the presence of nucleotide triphosphate and magnesium ions. The results suggested that favipiravir shows two distinct mechanisms in various viruses: RdRp active site inhibition and/or genome replication inhibition.

The number of patients with SARS-CoV-2 infection continues to increase, and it has become a global pandemic. Although there is an urgent need to establish an effective treatment, the medication available for dialysis patients has been limited. An antibody cocktail containing two SARS-CoV-2-neutrarizing antibodies, REGN-COV2 has been granted special approval for COVID-19 in Japan, since July 2021, and this intravenous preparation can be used for dialysis patients. At our hospital, we had 22 hemodialysis patients with COVID-19, and five of them were treated with REGN-COV2. On admission, four of the five patients had moderate disease (pneumonia but O2 inhalation) and one patient had mild disease (not having pneumonia). The mean duration of hospitalization treated with REGN-COV2 was 10.2 ± 2.86 days (mean ± SD), which was less than half, compared to patients untreated of similar severity on admission (22.12 ± 15.5). The time to fever resolution was average 7 days, and no cases progressed to severe illness or death. Among these patients, no obvious adverse reactions were shown. Although more studies with a larger number of patients could be needed for a rigorous evaluation of the effect, our result suggests that REGN-COV2 may be safe and having the possibilities in preventing severe disease in hemodialysis patients. Given the difficulty in securing inpatient beds tend to be in short supply, the strategy combined with neutralizing antibody could be beneficial for end-stage kidney disease (ESKD) patients with hemodialysis who are at high risk of severe disease.