Background: Wheezing phenotypes in young children have usually been described on the basis of questionnaire surveys instead of prospectively doctor-diagnosed episodes, and have never been described in terms of incidence rates. Aims: To identify wheezing phenotypes in the first three years and describe their incidence trends, and to investigate their relationship with asthma at six years of age. Methods: Doctor-diagnosed wheezing episodes in the first 36 months and active asthma at six years were identified in a historical cohort of 3,739 children followed from birth in 29 primary care health centres in Spain. Wheezing phenotypes were identified by means of latent class analysis. Changes in incidence rates of wheezing were identified through joinpoint regression models and their predictive ability for asthma was analysed. Results: One never/infrequent wheeze phenotype and three wheezing phenotypes were identified. There were two early phenotypes which started wheezing at a median age of six months, one of which was transient while the other had a heavy recurrence of episodes. A third phenotype exhibited a delayed onset of wheezing, a constant rise in incidence through the first 36 months, and a relationship with allergic asthma. These three phenotypes had a higher prevalence of active asthma at six years than the never/infrequent wheeze phenotype, but the classification had a weak predictive ability for asthma due to low sensitivity. Conclusions: The use of incidence rates contributes to the clarification of the natural history of infant wheezing.

Background Updated seroprevalence estimates are important to describe the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) landscape and to guide public health decisions. The aims are to describe longitudinal changes in seroprevalence in children in a region in Northern Spain and to analyze factors associated with SARS-CoV-2 seropositivity. Methods Prospective multicenter longitudinal study with subjects recruited from July to September 2020. Children (up to 14 years old) were included and followed up until September 2021. Venous blood samples were collected every six months during three testing rounds and were analyzed for SARS-CoV-2 antibodies. The data regarding epidemiological features, contact tracing, symptoms, and virological tests were collected. The evolution of SARS-CoV-2 seroprevalence during the study and the differences between children with positive and negative SARS-CoV-2 antibody tests were analyzed. Results Two hundred children were recruited (50.5% girls, median age 9.7 years). The overall seroprevalence increased from round 1 [1.5%, 95% confidence interval (CI) 0.3%–4.3%] to round 2 (9.1%, 95% CI 4.6%–12.7%) and round 3 (16.6%, 95% CI 9.5%–19.6%) ( P < 0.001). Main changes occurred in children aged zero to four years ( P = 0.001) who lived in urban areas ( P < 0.001). None of the children who were previously positive became seronegative. Following multivariable analysis, three variables independently associated with SARS-CoV-2 seropositivity were identified: close contact with coronavirus disease 2019 (COVID-19) confirmed or suspected cases [odds ratio (OR) = 3.9, 95% CI 1.2–12.5], previous positive virological test (OR = 17.1, 95% CI 3.7–78.3) and fatigue (OR = 18.1, 95% CI 1.7–193.4). Conclusions SARS-CoV-2 seroprevalence in children has remarkably increased during the time of our study. Fatigue was the only COVID-19-compatible symptom that was more frequent in seropositive than in seronegative children.