Incidence, Prevalence, and Mortality of Interstitial Lung Diseases in Alberta, Canada: A Population-based Study by Johannson et al. published in Annals of American Thoracic Society (2025). https://doi.org/10.1513/AnnalsATS.202406-625OC
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Lay Summary
Why We Did This Study:
The Interstitial Lung Diseases (ILDs) are a group of lung conditions that cause inflammation and scarring in the lungs, often leading to shortness of breath, chronic cough and in many cases, early death. There are many different types of ILDs, and they often go unrecognized or are diagnosed late, so it is hard to estimate how many people are actually affected. We think that the number of people living with ILD is probably underestimated. Using Alberta’s health registry within a universal healthcare system, this study aimed to best capture the entire provincial population to better understand how many people are affected by ILD, and whether the number of people diagnosed with ILD is changing overtime.
Incidence (new cases) and prevalence (total cases) explanation:
Incidence and prevalence are two ways to measure how common a disease is in a population. Incidence is the number of new cases that develop during a specific period of time. Prevalence is the total number of people living with the condition at any specific point in time. For example, if 10 people in Alberta develop ILD in one year, the incidence is 10. If 50 people in Alberta are living with ILD at the time, then the prevalence is 50.
Study Goals:
The main goal of this study was to determine how common Interstitial Lung Disease (ILD) is in Alberta by observing how many new and existing cases occurred over a 10-year period from 2010-2019. The second goal was to determine how many people with ILD died over the same 10-year period. The 10-year study period will also allow for trends to be observed in changes to ILD incidence, prevalence, and mortality.
How The Study Was Done:
To confirm that researchers could accurately identify patients with ILD, we first compared 412 people known to have ILD to 1648 similar people (by age and sex) who did not have ILD. Our methods correctly identified patients with ILD from electronic records 96% of the time (which is pretty good).
Researchers then looked at the whole adult population of Alberta using the Alberta Health Services database between 2010 and 2019. ILD patients were identified using the verified algorithm. Alberta’s universal healthcare system includes almost 100% population coverage within the province, so we were confident we found all the cases. Incident (new cases) and prevalence (total cases) were calculated for every 100 000 adults. Researchers also recorded deaths from any cause and lung transplants that occurred during the study period.
Findings:
The study included approximately 5.6 million adults living in Alberta. Researchers identified approximately 42 5000 people living with ILD (prevalence) and approximately 31 500 new cases (incidence) over the 10 years. About 55% of people with ILDs were male. Nearly 75% of ILD patients lived in major cities. The average age at diagnosis was 62 years, and ILD became more common as people got older. Idiopathic pulmonary fibrosis (IPF)was the most common type of ILD, accounting for 1/3 of all cases. Other forms of ILD identified included, connective tissue disease-associated ILD, hypersensitivity pneumonitis, pneumoconiosis and ‘other’ less common forms grouped together.
On average, there were about 100 new ILD cases per 100 000 adults each year. The number of new cases per year did not increase or change over the 10-year study period. However, the total number of people living with ILD increased from 375 per 100 000 adults in 2010 to 779 per 100,000 adults in 2019. This increase was seen across all major ILD subtypes. This number is similar to the number of people living with Celiac disease, meaning it is not rare.
Of the approximately 31,500 people newly diagnosed with ILD, about 8 700 (27%) died within over the 10 years of the study. Meanwhile about 500, (only 2%) received a lung transplant. People with IPF had the highest risk of death or lung transplant within three years of diagnosis. People with IPF were living longer in 2019 compared to 2010, meaning that survival improved during the study period.
Interpretation:
Over the 10-year study period, the number of new cases of ILD each year did not change. The increased total number of people living with ILD (prevalence) may be partly explained by improved survival over the same period. Newly available medications may explain some of the improved survival, though the study does not explicitly prove this.
Using the Alberta province-wide health registry allowed researchers to identify more people with ILD than previous studies have shown. These new estimates demonstrate a much higher ILD burden on patients and the healthcare system than previously thought. Findings suggest global underestimates of ILD burden overall and across specific diagnostic groups.
Researcher also found that ILD was more common in rural areas than in urban areas. This is important because people living in rural communities may have more difficulty accessing specialist care
Summary:
Understanding how many people develop and live with ILD can help healthcare systems plan resources and improve access to care. The researchers first confirmed their method for identifying ILD patients was accurate, giving greater confidence that this study reflects the true number of people with ILD in Alberta. During this 10-year study period from 2010-2019 the incidence of ILD was stable, while the prevalence increased and mortality decreased. Estimates of ILD from this study are higher than previous studies, suggesting a higher impact on the health systems than previously imagined. This further suggests a global underestimation of ILD burden.
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