Rates of hospitalization and in-hospital mortality dropped significantly for people with idiopathic pulmonary fibrosis (IPF) in the U.S. between 2006 and 2016, and hospitalizations were most common in colder months, an analyses of disease trends found.
The study, “Trends and seasonal variation of hospitalization and mortality of interstitial lung disease in the United States from 2006 to 2016,” was published in the journal Respiratory Research.
Pulmonary fibrosis is part of a larger group of respiratory disorders, generally known as interstitial lung diseases (ILD), characterized by inflammation and scarring. Idiopathic (of unknown origin) pulmonary fibrosis is the most common form of ILD.
Investigators at Saint Louis University Hospital in Missouri collected long-term information on ILD patients using from the Nationwide Inpatient Sample database. Their goal was to better understand both seasonal variation — known to affect exacerbations and lung health in people with these disorders — and recent advances in treating ILDs by looking at trends in hospital admission and mortality rates over the last decade.
In the overall ILD group, hospital admission rates for patients significantly declined over the 11 years examined, regardless of pneumonia status.
This group’s monthly hospitalization rate per 1 million people ranged from 6.9 in July to 8 in April, with January to April showing the highest number of admissions compared with other months. This seasonal pattern of hospitalization rates remained the same even when infectious pneumonia cases were excluded.
When months were considered as part of the four seasons, inter-seasonal differences did not reach statistical significance. However, compared to winter, summer, and fall combined, a significantly higher number of hospitalizations occurred in the spring (March through May).
“The two most common explanations for winter and early Spring increase in admission rates are respiratory infection and cold temperature,” the researchers wrote. “Cold air could hypothetically induce hyperpnoea [increased rate of breathing], subsequently cause drying of the airways and inducing proinflammatory substances production leading to epithelial injury.”
Mortality rates for ILD patients also changed with seasons, with the highest rate being observed in the winter (December through February), particularly in the months of December and February.
Unlike hospital admission rates, however, mortality rates for ILD did not decrease over these 11 years. “Respiratory causes of death accounted for 64–89% in patients with ILD,” the researchers wrote.
Within the IPF subgroup, whose patients accounted for 88% of all hospital admissions in 2006–16, a statistically significant downward trend was seen in both hospitalizations and mortality. But mortality rates did not differ greatly by month or season, with the highest hospitalization rates in these patients occurring from January to April.
“One hypothesis could be the severity of IPF related admissions and pneumonia has no weather association,” they suggested.
Among ILD patients with acute respiratory failure, hospital rates rose by threefold over the 11 years studied, while mortality rates lowered by two times. Neither mortality and hospital admission rates significantly varied due to season, although slightly higher admission rates were reported in winter.
Pneumonia patients had the highest hospitalization rates in December to April, and these decreased over time. Pneumonia mortality rates remained constant both across months and seasons, and throughout the 11-year period.
“From 2006 to 2016, admission rates of ILD of all causes and IPF subgroup declined but in-hospital mortality of ILD of all causes remained unchanged,” the researchers wrote. “All-cause hospital admissions and mortality of ILD have a strong seasonal variation.”
“Hospitalization rates for all subgroups (IPF, ARF, pneumonia) were highest in the months from December to April,” they added, again supporting seasonal changes in weather as important factors in patients’ well-being.
And while all-cause mortality for “interstitial lung disease from 2006 to 2016 has been unchanged … the all-cause mortality rate of idiopathic pulmonary fibrosis subgroup encouragingly decreased in this 11-year period,” the researchers concluded.
“Anti-fibrotic treatment availability could be a possible explanation … However, it is challenging to pinpoint a single factor that lead to this encouraging result based on our study especially when antifibrotic therapies were only approved since 2014.”
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