Infection by RNA viruses is detected by the host through Toll-like receptors or RIG-I-like receptors. Toll-like receptors and RIG-I-like receptors signal through the adaptors MyD88 and MAVS, respectively, to induce type I IFNs (IFN-I) and other antiviral molecules, which are thought to be essential for activating the adaptive immune system. We investigated the role of these adaptors in innate and adaptive immune responses against respiratory syncytial virus (RSV), a common human pathogen. Deletion ofMavsabolished the induction of IFN-I and other proinflammatory cytokines by RSV. Genome-wide expression profiling in the lung showed that the vast majority of RSV-induced genes depended on MAVS. AlthoughMyd88deficiency did not affect most RSV-induced genes, mice lacking both adaptors harbored a higher and more prolonged viral load and exhibited more severe pulmonary disease than those lacking either adaptor alone. Surprisingly,Myd88^−/−Mavs^−/−mice were able to activate a subset of pulmonary dendritic cells that traffic to the draining lymph node in response to RSV. These mice subsequently mounted a normal cytotoxic T-lymphocyte response and demonstrated delayed but effective viral clearance. These results provide an example of a normal and effective adaptive immune response in the absence of innate immunity mediated by MAVS and MyD88.

To describe the clinical and epidemiological characteristics of hospitalized children with multisystem inflammatory syndrome in children (MIS-C) in Santiago, Chile. This was an observational study of children with MIS-C (May 1 to June 24, 2020), in three pediatric hospitals in Santiago. Demographic characteristics and epidemiological data, medical history, laboratory tests, cardiology evaluations, treatment, and clinical outcomes were analyzed. Twenty-seven patients were admitted (median age 6, range 0–14 years). Sixteen of the 27 (59%) required intensive care unit admission; there were no deaths. Seventy-four percent had no comorbidities, and the median number of days of symptoms before admission was 4 (range 2–9 days). Gastrointestinal symptoms were the most frequent, and inflammatory markers were increased at admission. A recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was detected in 82% of cases. The severe group showed significantly lower hemoglobin and albumin levels, decreased platelet counts, and higher d-dimer during disease evolution. Echocardiography showed abnormalities (myocardial, pericardial, or coronary) in 12 patients (46%) during their hospital stay. Anti-inflammatory treatment (immunoglobulin and/or corticosteroids) was prescribed in 24 patients. MIS-C appeared in clusters weeks after the peak of SARS-CoV-2 cases, especially in the most vulnerable areas of Santiago. This study describes the first series (n = 27) of children with MIS-C in a Latin American country, showing favorable clinical outcomes. Education and alerts are required for clinical teams to establish an early diagnosis and prompt treatment.

Background. Systemic steroids have been advocated in addition to antimicrobial therapy for severe Mycoplasma pneumoniae pneumonia. We evaluated the ef

The role of respiratory viral infections (RVIs) as a cause of overall fever and neutropenia (FN) episodes in children with cancer has been less characterized than bacterial infections. We conducted a study aimed to determine the frequency of RVI in children with low compared with high risk for invasive bacterial infection (IBI) FN episodes and compare the clinical outcome of RVI and mixed RV-bacterial infections. Prospective, multicenter study in children with cancer and FN admitted to pediatric hospitals in Chile between May 2009 and January 2011. Children were evaluated by clinical examination and laboratory tests, including bacterial cultures and their risk for IBI. Nasopharyngeal sample was obtained for the detection of 17 respiratory viruses using polymerase chain reaction-DNA microarray platform. A total of 331 episodes of FN in 193 children were enrolled of whom 55% were male, with the median age of 7 years and 61% had a hematological malignancy. A viral and/or bacterial pathogen was detected in 67% (224/331) episodes. Overall, RVIs were associated with 57% of FN of which one-third were mixed RV-bacterial infections. Bacterial infection was detected in 29% (97/331). Children classified at admission as high risk for IBI had a similar overall proportion of RVI compared with low-risk group. Respiratory syncytial virus (31%) and rhinovirus (23%) were the most frequently detected respiratory viruses, followed by parainfluenza (12%) and influenza A (11%). Children detected with any respiratory virus had fewer days of hospitalization and a significantly lower probability of hypotension and admission to pediatric intensive care unit irrespective of their risk classification status at admission when compared with children with mixed RV-bacterial or bacterial infections (P < 0.05). All children with a sole RVI had favorable outcome. RVIs were the most frequently detected agents irrespective of their initial risk assessment for IBI. The clinical outcome of mixed RVI was similar to sole RVI episodes as well as for bacterial infections compared with mixed viral-bacterial infections. Systematic and early detection of RVI in children with cancer and FN might help to optimize their management by reducing hospitalization and antimicrobial use.

Background. In Chile, the novel influenza A (H1N1) epidemic began in the middle-high income area of Santiago. Clinical and laboratory surveillance wa