In the recent years, the overall trends in hospital admission and mortality of interstitial lung disease (ILD) are unknown. In addition, there was some evidence that interstitial lung disease death rate highest in the winter but this finding was only available in one study. This study will investigate the trend and seasonal variations in hospital admission and mortality rates of ILD from 2006 to 2016.
From the Nationwide Inpatient Sample database, we collected all cases with the International Classification of Diseases (ICD)-9 or ICD-10 codes of ILD excluding identifiable external causes (drug, organic or inorganic dusts) from 2006 to 2016. Hospitalization rates of each year were calculated based on U.S Census population data. Monthly hospitalization and in-hospital mortality rates were analyzed by seasonal and trend decomposition.
From 2006 to 2016, there was a downtrend in all cause hospital admissions but in-hospital mortality rate did not change, with or without the presence of pneumonia. Highest hospital admission rates of ILD per 100000 of population were from January to May. The average number of hospitalizations in spring, summer, fall and winter months were 7447.9 ± 932.0, 6643.0 ± 840.5, 6551.3 ± 922.6 and 7110.3 ± 866.1 respectively. All-cause in-hospital mortality ranges from 7.13% ± 0.79% in the summer to 8.13% ± 0.60% in the winter with winter months having the highest mortality rate (p=0.018). The seasonal variations of hospital admission and mortality was not changed when infectious pneumonia cases were ruled out.
From 2006 to 2016, admission rates of ILD declined but in-hospital mortality remained unchanged. All-cause hospital admissions and mortality of ILD have a strong seasonal variation. Hospital admissions are highest in the period from January to May, in-hospital death was highest in the winter.