In the U.S., idiopathic pulmonary fibrosis (IPF) mortality rates decreased from 2004 to 2017, a new study shows.
The data suggests the decline might be partly explained by a decline in smoking, but further research is needed to better understand the factors contributing to this trend.
The study, “Mortality Trends of Idiopathic Pulmonary Fibrosis in the United States from 2004 to 2017,” was published in the journal CHEST.
Previous research suggested that IPF mortality rates increased in the U.S. from 1979 to 2003, and predicted that trend might continue. However, in recent years there have been substantial improvements in the diagnosis and treatment of IPF, warranting a more up-to-date analysis.
To that end, a team led by researchers at Loma Linda University Health in California analyzed data from the Centers for Disease Control and Prevention (CDC)’s Multiple Cause of Death Database, which records demographic and cause-of-death data for U.S. residents. (Of note, the aforementioned previous studies also have accessed this databased.)
There were 35,625,719 recorded deaths in the U.S. from 2004 to 2017. Of those, 274,995 (0.7%) had a recorded diagnosis of pulmonary fibrosis. The researchers excluded 14,051 cases in which pulmonary fibrosis could be explained by other recorded conditions; the remaining 260,944 deceased were considered as having IPF.
The database code that the researchers used to identify these deaths “is not specific to IPF and can be used for other interstitial lung diseases with fibrosis,” the researchers wrote. “However, by carefully excluding decedents with other secondary conditions associated with pulmonary fibrosis, we believe we were able to isolate a group more likely to have IPF.”
The team then calculated the IPF mortality rate per 1 million population, at different points in time and among different demographic groups.
Overall, the IPF mortality rate per 1 million population was 58.0 in 2004 and 53.7 in 2017. Statistical analysis suggested a significant “negative temporal trend.” That means mortality rates decreased over time in a manner not attributable to random chance.
In sex-classified analyses, the IPF mortality rate decrease was statistically significant for females (from 46.3 in 2004 to 40.1 in 2017), but not for males (from 75.5 in 2004 to 72.4 in 2017), though the same trend was seen in both groups.
In both sexes, IPF mortality rates significantly decreased over time for age groups between 45 and 84 years, while IPF mortality rates for the age group of 85 and older increased (in males) or did not significantly change (in females).
Overall, the age-adjusted mortality decreased by 4.1% in males and by 13.4% in females. According to the team, “this overall decrease was mainly driven by a decline in IPF-related mortality in patients younger than 85 years of age.”
In race-classified analyses, IPF mortality rates significantly decreased over the studied time period for all groups analyzed (namely Native Americans, Hispanics, Asians, and Blacks) except for white males, in whom IPF mortality rates remained stable over time.
Generally, mortality rates were highest in Native Americans, lowest in Asians and Blacks, with whites and Hispanics in between.
Overall, and “contrary to previous studies, we noted a decline in age-adjusted mortality rates … from 2004 to 2017,” the researchers wrote.
According to the team, there are several possible explanations for this trend: “decreasing incidence of IPF, increased survival time, and failure to list IPF as a cause of death are potential causes for the declining IPF-related mortality rate.”
Researchers speculated that decreasing incidence of IPF might be the most likely explanation. In particular, they noted that smoking, a known risk factor for IPF, has become less common in the U.S. since the 1960s.
This also may explain age-based differences in mortality. “Older patients are more likely to have had a significant smoking history,” the researchers wrote. Better care also could result in more people living past 85, ultimately resulting in more deaths in this oldest group.
Smoking might explain some of the noted differences in race. “Smoking rates are highest among Native Americans and lowest in Asians and Blacks which could partly explain the mortality differences,” the researchers wrote. However, they noted that this does not fully explain the disparity, writing, “Hispanics have a lower smoking rate, however, mortality rates were comparable to Whites.”
As such, other factors also are likely at play.
The researchers cited access to care as an important factor. “Blacks are less likely to be diagnosed with IPF than whites since they are less likely to have appropriate primary and sub-specialist care,” they wrote.
Overall, “further validation studies are warranted to examine possible factors contributing to this decline in IPF-related mortality. The increased IPF related mortality rate in ethnic groups such as Native Americans also warrants further investigation into the role of genetic and environmental factors,” the researchers wrote.
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