International Variation in Severe Exacerbation Rates in Patients With Severe Asthma.

BACKGROUND: Exacerbation frequency strongly influences treatment choices in patients with severe asthma. RESEARCH QUESTION: What is the extent of the variability of exacerbation rate across countries and its implications in disease management? STUDY DESIGN AND METHODS: We retrieved data from the International Severe Asthma Registry, an international observational cohort of patients with a clinical diagnosis of severe asthma. We identified patients aged ≥ 18 years who did not initiate any biologics prior to baseline visit. A severe exacerbation was defined as the use of oral corticosteroids for ≥ 3 days or asthma-related hospitalization/ED visit. A series of negative binomial models were applied to estimate country-specific severe exacerbation rates during 365 days of follow-up, starting from a naive model with country as the only variable to an adjusted model with country as a random-effect term and patient and disease characteristics as independent variables. RESULTS: The final sample included 7,510 patients from 17 countries (56% from the United States), contributing to 1,939 severe exacerbations (0.27/person-year). There was large between-country variation in observed severe exacerbation rate (minimum, 0.04 [Argentina]; maximum, 0.88 [Saudi Arabia]; interquartile range, 0.13-0.54), which remained substantial after adjusting for patient characteristics and sampling variability (interquartile range, 0.16-0.39). INTERPRETATION: Individuals with similar patient characteristics but coming from different jurisdictions have varied severe exacerbation risks, even after controlling for patient and disease characteristics. This suggests unknown patient factors or system-level variations at play. Disease management guidelines should recognize such between-country variability. Risk prediction models that are calibrated for each jurisdiction will be needed to optimize treatment strategies.

The increasing burden of asthma acute care in Singapore: an update on 15-year population-level evidence.

BACKGROUND: In Singapore, there is currently scarce population-based research informing the recent trends of asthma-related healthcare burdens. In this study, we investigated the past 25-year trends of asthma-related hospitalisations, emergency department (ED) visits and deaths in Singapore and projected the future burdens from 2023 to 2040. METHODS: We acquired annually-measured data from the Singapore Ministry of Health Clinical and National Disease Registry, containing 25-year asthma-related hospitalisation and death rates as well as 15-year ED visit rates. We conducted change-point analysis and generalised linear modelling to identify time intervals with stable trends and estimate asthma-related healthcare utilisation and mortality rates. To project future asthma-related burdens, we developed a probabilistic model which combined projections of future population size with the estimated rate outcomes from the last stable period. RESULTS: Our results show that the asthma hospitalisation rate in Singapore had remained at approximately 80 episodes per 100,000 from 2003 to 2019 and are likely to grow by 1.7% each year (95% CI: 0.7, 5.0%), leading to a total of 163,633 episodes from 2023 to 2040 which corresponds to an estimated $103,075,820 based on 2022 USD. Besides, Singapore's asthma-related ED visit rate was 390 per 100,000 in 2019 and is expected to decline by 3.4% each year (95% CI: - 5.8, 0.0%), leading to a total of 208,145 episodes from 2023 to 2040 which corresponds to USD$15,053,795. In contrast, the 2019 asthma-related mortality rate in Singapore was approximately 0.57 per 100,000 and is likely to stay stably low (change per year: -1.3, 95% CI: - 11.0, 4.3%). Between 2023 and 2040, Singapore's estimated total number of asthma-related deaths is 638 episodes. CONCLUSIONS: Currently, the burden of asthma acute care in Singapore is high; Singapore's asthma-related hospitalisation and ED visit rates are relatively higher than those of other developed economies, and its asthma admission rate is expected to increase significantly over time, possibly indicating excess resource use for asthma. The established national asthma programme in Singapore, together with recent efforts in reinforcing primary care at the national level, provides opportunities to reduce avoidable asthma admissions.

Impact of Guideline-Based Asthma Treatment on Health Services Use in Singapore Before and During COVID-19 Outbreak.

Introduction: To date, the role of standard asthma care in reducing asthma-related health services use (HSU) during the COVID-19 pandemic remains unclear. This study examined the impact of guideline-based asthma treatment on the use of asthma-related emergency department (ED) visits, polyclinic visits (total visits and urgent visits characterized by nebuliser use) before and during the pandemic. Methods: Data from April 2017 to October 2020 was obtained from the National University Health System, one of the three healthcare clusters in Singapore. Using generalized linear models, we estimated the joint effects of the ratio of preventer to reliever dispensations (PRR) and COVID-19 on asthma-related ED visits per hospital per month, total asthma-related polyclinic visits and asthma-related urgent polyclinic visits per clinic per month. Results: Findings show that before the onset of COVID-19, for every 0.5 unit increase in PRR, the number of asthma-related ED visits and urgent polyclinic visits decreased by 12.9% (95% CI: -13.0% to -12.9%) and 6.8% (95% CI: -6.9% to -6.7%), respectively, whereas total asthma-related polyclinic visits increased by 1.0% (95% CI: 0.9% to 1.0%). During the pandemic, a 0.5 unit increase of PRR decreased the number of asthma-related ED visits, urgent and total polyclinic visits by 16.9% (95% CI: -17.0% to - 16.9%), 9.3% (95% CI: -9.5% to -9.2%) and 0.7% (95% CI: -0.8% to -0.7%), respectively. Discussion: These findings suggest that regardless of the COVID-19 pandemic, an increase in PRR consistently reduced the frequency of asthma-related urgent and emergent care, although it barely influenced routine asthma follow-up visits.

Mediation analysis with multiple mediators under unmeasured mediator-outcome confounding.

It is often of interest in the health and social sciences to investigate the joint mediation effects of multiple post-exposure mediating variables. Identification of such joint mediation effects generally require no unmeasured confounding of the outcome with respect to the whole set of mediators. As the number of mediators under consideration grows, this key assumption is likely to be violated as it is often infeasible to intervene on any of the mediators. In this article, we develop a simple two-step method of moments estimation procedure to assess mediation with multiple mediators simultaneously in the presence of potential unmeasured mediator-outcome confounding. Our identification result leverages heterogeneity of the population exposure effect on the mediators, which is plausible under a variety of empirical settings. The proposed estimators are illustrated through both simulations and an application to evaluate the mediating effects of post-traumatic stress disorder symptoms in the association between self-efficacy and fatigue among health care workers during the COVID-19 outbreak.