We conducted a population study of ED visit volume, acuity, and hospital admission rates for asthma in Alberta, Canada. The primary findings of this study are: (1) the incidence of ED visits for asthma has decreased since 2010, (2) the acuity of asthma patients in the ED has simultaneously increased, and (3) the percent of ED visits for asthma resulting in hospital admission has increased.

This study builds on the work of Rosychuk et al. that looked at an earlier time period in Alberta, 1999–2011 [3]. They found that the number of ED visits for asthma in adults declined from 19.3 to 8.5 per million per day over this period. There was an associated decline in hospital admissions, from 10.3 to 6.9%. They hypothesized that better asthma therapeutics, non-pharmacological interventions, and health care access outside the ED were responsible for these improvements. This study demonstrates a continued, albeit gradual decline in ED visits, from 4.5 to 2.2 per million per day from 2010 to 2022. Unfortunately, the hospitalization trend has reversed, and there was a concomitant increase from 6.8 to 11.3%. The situation has become more complex as fewer asthmatics sought care in the ED, and those who did go to the ED were more acute and more likely to require hospitalization. Over the study period, the high-acuity ED visits (CTAS 1) increased by 3.7 fold in males and 3.1 fold in females.

It would be reassuring to state that fewer asthmatics presented to the ED because of better symptom control in the community, but that was probably not the case. Moitra et al. showed that the prescription of asthma controller inhalers in Alberta, including ICS, remained stable from 2008 to 2020 despite the increasing prevalence of asthma [2]. The Canadian obesity rate increased over the study period, asthmatics are more likely to develop obesity than the general population, and this would be associated with worse asthma outcomes [7,8,9]. The study period includes the legalization of cannabis in Canada in 2018, and the advent of electronic cigarettes. Forest fires have become more frequent and are associated with worse asthma control [10]. It is more likely that the number of poorly controlled asthmatics in the community has increased, and they have become less likely to visit the ED for mild or moderate exacerbations over the years. Multiple epidemiologic studies have theorized that ED overcrowding affects asthma patients’ decision to visit the ED [3, 4, 11]. This study suggests that patients who present to the ED regardless of overcrowding are more likely to have severe exacerbations and require hospitalization. This is supported by Alberta data suggesting that patients with the most severe exacerbations required increasing time in the ED for stabilization from 2011 to 2015 [12].

Lee et al. examined Canada-wide trends in asthma hospitalization from 2002–2017 [4]. They found a major improvement in hospitalization rates from 2002 to 2010, and a subsequent stabilization until 2017. They posited that advances in asthma therapeutics, like ICS/LABA, combined with non-pharmacologic approaches greatly improved asthma control until about 2010. Thereafter, there was a “floor effect,” whereby only a subset of asthmatics continued to have severe exacerbations, resulting in a stabilization of asthma hospitalizations. These patients may have had asthma endotypes that were poorly responsive to existing therapies, or experienced systemic and socioeconomic barriers to health care.

With regards to Alberta, there probably was no “floor effect,” as the gradual decline in ED visits masked a dynamic and worsening situation between 2010 and 2022. This and other studies have shown a worsening of the population prevalence of asthma, the acuity of exacerbations in the ED, the percentage of asthmatics in the ED requiring hospitalization, and non-prescription of controller medications in recent years [2].

However, there are reasons for optimism, particularly for patients with adequate access to specialist health care. Given the Covid-19 pandemic disrupted pre-existing trends in asthma, it is probably too early to assess the effectiveness of biologics for asthma using real-world epidemiologic data. Guideline-based approaches to the use of ICS/LABA on demand may result in improved symptom control and exacerbation rates. Additionally, the development of mRNA vaccines for common respiratory viruses, such as rhinovirus, may also reduce exacerbation rates.

There were sex differences in our data, with women showing consistently higher rates of ED visits and hospitalization than men. This is consistent with prior Canadian data showing that elderly women are less likely to have spirometry, physician visits for asthma, or controller medication prescription than elderly men [13, 14]. In Alberta, women presenting to the ED for asthma are more likely to return within 30 days than men [15].

There are limitations of this study. First, the reliance on administrative healthcare data may be subject to coding errors or biases. Second, although we assessed sex-specific trends, other demographic factors and clinical variables, such as age and co-morbidities, were not included in this analysis, and this may have influenced asthma exacerbation rates. Third, the unique circumstances of the Covid-19 pandemic, which did affect ED visit and hospitalization rates in our data, deserve special attention, and this is beyond the scope of our study. Other investigators have commented on the reduction in the number of severe asthma exacerbations during the pandemic, and speculated on the reasons Additional file 1.