Does ILD Vary by Season for Hospitalization, Mortality Rates?

A recent study examined the trend and seasonal variations in US hospital admissions and mortality rates of interstitial lung disease (ILD) and found that winter is an especially perilous time for patients with ILD.

While ILD has new treatments, it remains a challenging respiratory disease, the researchers noted in Respiratory Research. Other respiratory diseases, such as chronic obstructive pulmonary disease and asthma, also have seasonal variations, but the impact of such variation on ILD is poorly understood. This is the first study to describe both seasonal variations of hospital admission and in-hospital mortality for idiopathic interstitial fibrosis (IPF) and non-IPF ILD, the researchers said.

To get a better understanding of mortality and admission trends, researchers used data from the Nationwide Inpatient Sample of Agency for Healthcare Resource and Quality Healthcare Cost and Utilization Project for the years 2006 to 2016. Hospitalization rates for each year were calculated based on US Census population data. Monthly hospitalization and in-hospital mortality rates were analyzed by seasonal and trend decomposition.

Analyzed subgroups included IPF, acute respiratory failure (ARF), and pneumonia.

All-cause hospital admission rate of patients ILD and IPF-only subgroup fell, but their overall mortality remained unchanged (except IPF subgroup and acute respiratory failure subgroup). Mortality of ILD in general and ILD with ARF was highest in winter, up to 8.13% (mean [SD] 0.60) and 26.3% (10.2%) respectively.

Admission rate for all-cause admissions were highest in from January to April. Subgroup analysis also showed seasonal variations with highest hospitalization rates for all subgroups (IPF, ARF, pneumonia) from December to April (ie, winter to early spring).

By IPF alone, which accounted for 88% of all ILD admissions in the study, hospitalization and mortality moved downwards over 11&thinsp;years (P&thinsp;<&thinsp;.05). IPF hospitalization rates were noted to be highest in the months from January to April compared with the rest of the months. Mortality rates were not different between months.

Admissions related to ARF accounted for 23% of all-cause admissions and pneumonia for 17.6%.

December and February saw the highest mortality (P&thinsp;=&thinsp;.018), when the months were grouped into seasons:

• Spring: 7.61% [0.67%]
• Summer: 7.13% [0.79%]
• Fall: 7.57% [0.69%]
• Winter: 8.13% [0.60%]

The presence or absence of infectious pneumonia did not significantly affect seasonal variation of mortality.

The authors said respiratory infection and cold temperature were likely reasons for the seasonal variability. Cold air might induce hyperpnoea, which could dry out airways and stimulate lung-damaging proinflammatory substances.

Reference

Ho ATN, Shmeley A, Charbek E. Trends and seasonal variation of hospitalization and mortality of interstitial lung disease in the United States from 2006 to 2016. Respir Res. Published online June 16, 2020. doi:10.1186/s12931-020-01421-0