Results
In 2013, 3086 questionnaires were distributed, 2643 were collected and, after those with missing or inconsistent data were excluded (N=89; 2.9%), 2554 questionnaires were analyzed. Telephone confirmation was achieved in 88.2% of the 254 positive responders and in 260 controls. Of the 3135 distributed questionnaires in 2018, 2719 were collected and 2648 were analyzed (questionnaires with missing or inconsistent data N=71; 2.3%). Telephone confirmation was achieved in 96% of the 174 positive responders and in 180 negative controls. The flow charts of the 2013 and 2018 surveys are presented in Figure 1. The overall sample included 285 children of non-Greek ethnic origin (11.2%; 8.8% Albanian) in 2013, and 270 in 2018 (10.2%; 7.6% Albanian).
Prevalence trends of current (persistent and recent-onset) and non-current wheeze/asthma are presented in Table 1 and in E-figure 2. A decreasing trend in the prevalence of current, persistent, and non-current wheeze/asthma was noted after 2008 (P for trend <0.001), while the prevalence of recent-onset wheeze/asthma during the same period remained stable (P for trend 0.964). The sex-adjusted prevalence rate ratio for current wheeze/asthma was 0.76 (95% CI 0.61-0.96) between 2008 and 2013, and 0.82 (0.64-1.06) between 2013 and 2018. The 2008-2013 and 2013-2018 prevalence rate ratios were significant for persistent and non-current wheeze/asthma, but not for the recent-onset symptoms (Figure 2).
The rates of children with physician-diagnosed asthma among those with physician-diagnosed wheeze are presented in Figure 3. Similar to the previous surveys, a diagnosis of recent-onset asthma was given to a smaller percentage of children with recent-onset wheeze (35.5% in 2013 and 37.2% in 2018), as compared to their counterparts with persistent asthma (65% of persistent wheeze in 2013 and 70% in 2018) or non-current asthma (87.4% of non-current wheeze in 2013 and 83.3% in 2018) (Figure 3, E-table 2. E-figure 3).
In 2018, 119 (68.4%) of the positive responders (65.1% of those with recent-onset wheeze/asthma, 69% of those with persistent wheeze/asthma, and 70% of those with non-current wheeze/asthma) as well as 85 controls (negative responders) underwent spirometry. The characteristics of these children are presented in E-table 3. Participants with recent-onset wheeze/asthma had lower FEV1 and FEF25-75 compared with their non-current wheeze/asthma counterparts or healthy controls ( Figure 4, E-table 4). Children with persistent wheeze/asthma had lower FEV1/FVC but comparable FEV1 and FEF25-75 with those with non-current wheeze/asthma or healthy controls (Figure 4, E-table 4). Of the participants with resent-onset and persistent wheeze/asthma, 32.1% and 22.4%, respectively, had FEV1 z-score less than –1 (Figure 5).