Acute respiratory distress syndrome (ARDS) is caused by infectious insults, such as pneumonia from various pathogens or related to other noninfectious events. Clinical and histopathologic characteristics are similar across severely affected patients, suggesting that a common mode of immune reaction may be involved in the immunopathogenesis of ARDS. There may be etiologic substances that have an affinity for respiratory cells and induce lung cell injury in cases of ARDS. These substances originate not only from pathogens, but also from injured host cells. At the molecular level, these substances have various sizes and biochemical characteristics, classifying them as protein substances and non-protein substances. Immune cells and immune proteins may recognize and act on these substances, including pathogenic proteins and peptides, depending upon the size and biochemical properties of the substances (this theory is known as the protein-homeostasis-system hypothesis). The severity or chronicity of ARDS depends on the amount of etiologic substances with corresponding immune reactions, the duration of the appearance of specific immune cells, or the repertoire of specific immune cells that control the substances. Therefore, treatment with early systemic immune modulators (corticosteroids and/or intravenous immunoglobulin) as soon as possible may reduce aberrant immune responses in the potential stage of ARDS.

To reveal the recent epidemiologic features of Kawasaki disease (KD) in South Korea based on data from a nationwide survey. We collected data between 2012 and 2014 regarding the incidence, symptoms and signs, treatment trends and coronary complications associated with acute KD by sending questionnaires to 97 hospitals with pediatric residency programs as well as 19 community hospitals without residency training. We received full and partial data from 97 and 13 hospitals, respectively (response rate: 94.8%). A total of 14,916 cases of KD were reported by these 110 hospitals (4588 in 2012, 5183 in 2013 and 5145 in 2014). The male-to-female ratio was 1.4:1, and the median age at diagnosis was 29 months. The incidence of KD per 100,000 children younger than 5 years of age were 170.9, 194.9 and 194.7 in 2012, 2013 and 2014, respectively. The recurrence rate was 4.7%. KD occurred more frequently during summer (especially June and July) and winter (December and January) seasons. Intravenous immunoglobulin was administered to 95.4% of the patients, and the nonresponder rate for the first intravenous immunoglobulin was 11.8%. Coronary aneurysm occurred in 1.7% of the patients, and giant aneurysm developed in 19 patients (0.16%) during the 3 years. One patient had myocardial infarction and 1 patient died of suspected coronary aneurysm rupture. The incidence of KD in South Korea increased to 194.7 per 100,000 children younger than 5 years in 2014; meanwhile, the coronary aneurysm rate decreased to 1.7%.

Mycoplasma pneumoniae (MP), the smallest self-replicating biological system, is a common cause of upper and lower respiratory tract infections, leading to a wide range of pulmonary and extra-pulmonary manifestations. MP pneumonia has been reported in 10 to 40% of cases of community-acquired pneumonia and shows an even higher proportion during epidemics. MP infection is endemic in larger communities of the world with cyclic epidemics every 3 to 7 years. In Korea, 3 to 4-year cycles have been observed from the mid-1980s to present. Although a variety of serologic assays and polymerase chain reaction (PCR) techniques are available for the diagnosis of MP infections, early diagnosis of MP pneumonia is limited by the lack of immunoglobulin (Ig) M antibodies and variable PCR results in the early stages of the infection. Thus, short-term paired IgM serologic tests may be mandatory for an early and definitive diagnosis. MP infection is usually a mild and self-limiting disease without specific treatment, and if needed, macrolides are generally used as a first-choice drug for children. Recently, macrolide-resistant MP strains have been reported worldwide. However, there are few reports of apparent treatment failure, such as progression of pneumonia to acute respiratory distress syndrome despite macrolide treatment. The immunopathogenesis of MP pneumonia is believed to be a hyperimmune reaction of the host to the insults from MP infection, including cytokine overproduction and immune cell activation (T cells). In this context, immunomodulatory treatment (corticosteroids or/and intravenous Ig), in addition to antibiotic treatment, might be considered for patients with severe infection.

Background: M. pneumoniae pneumonia (MP) has been reported in 10-40% of community-acquired pneumonia cases. We aimed to evaluate the difference of clinical features in children with MP, according to their age and chest radiographic patterns. Methods: The diagnosis of MP was made by examinations at both admission and discharge and by two serologic tests: the indirect microparticle agglutinin assay (≥1:40) and the cold agglutinins titer (≥1:32). A total of 191 children with MP were grouped by age: ≤2 years of age (29 patients), 3-5 years of age (81 patients), and ≥6 years of age (81 patients). They were also grouped by pneumonia pattern: bronchopneumonia group (96 patients) and segmental/lobar pneumonia group (95 patients). Results: Eighty-six patients (45%) were seroconverters, and the others showed increased antibody titers during hospitalization. Among the three age groups, the oldest children showed the longest duration of fever, highest C-reactive protein (CRP) values, and the most severe pneumonia pattern. The patients with segmental/lobar pneumonia were older and had longer fever duration and lower white blood cell (WBC) and lymphocyte counts, compared with those with bronchopneumonia. The patient group with the most severe pulmonary lesions had the most prolonged fever, highest CRP, highest rate of seroconverters, and lowest lymphocyte counts. Thrombocytosis was observed in 8% of patients at admission, but in 33% of patients at discharge. Conclusions: In MP, older children had more prolonged fever and more severe pulmonary lesions. The severity of pulmonary lesions was associated with the absence of diagnostic IgM antibodies at presentation and lymphocyte count. Short-term paired IgM serologic test may be mandatory for early and definitive diagnosis of MP.