Short term exposure to fine particulate matter and hospital admission risks and costs in the Medicare population: time stratified, case crossover study

OBJECTIVE: To assess risks and costs of hospital admission associated with short term exposure to fine particulate matter with diameter less than 2.5 µm (PM(2.5)) for 214 mutually exclusive disease groups. DESIGN: Time stratified, case crossover analyses with conditional logistic regressions adjusted for non-linear confounding effects of meteorological variables. SETTING: Medicare inpatient hospital claims in the United States, 2000-12 (n=95 277 169). PARTICIPANTS: All Medicare fee-for-service beneficiaries aged 65 or older admitted to hospital. MAIN OUTCOME MEASURES: Risk of hospital admission, number of admissions, days in hospital, inpatient and post-acute care costs, and value of statistical life (that is, the economic value used to measure the cost of avoiding a death) due to the lives lost at discharge for 214 disease groups. RESULTS: Positive associations between short term exposure to PM(2.5) and risk of hospital admission were found for several prevalent but rarely studied diseases, such as septicemia, fluid and electrolyte disorders, and acute and unspecified renal failure. Positive associations were also found between risk of hospital admission and cardiovascular and respiratory diseases, Parkinson’s disease, diabetes, phlebitis, thrombophlebitis, and thromboembolism, confirming previously published results. These associations remained consistent when restricted to days with a daily PM(2.5) concentration below the WHO air quality guideline for the 24 hour average exposure to PM(2.5). For the rarely studied diseases, each 1 µg/m(3) increase in short term PM(2.5) was associated with an annual increase of 2050 hospital admissions (95% confidence interval 1914 to 2187 admissions), 12 216 days in hospital (11 358 to 13 075), US$31m (£24m, €28m; $29m to $34m) in inpatient and post-acute care costs, and $2.5bn ($2.0bn to $2.9bn) in value of statistical life. For diseases with a previously known association, each 1 µg/m(3) increase in short term exposure to PM(2.5) was associated with an annual increase of 3642 hospital admissions (3434 to 3851), 20 098 days in hospital (18 950 to 21 247), $69m ($65m to $73m) in inpatient and post-acute care costs, and $4.1bn ($3.5bn to $4.7bn) in value of statistical life. CONCLUSIONS: New causes and previously identified causes of hospital admission associated with short term exposure to PM(2.5) were found. These associations remained even at a daily PM(2.5) concentration below the WHO 24 hour guideline. Substantial economic costs were linked to a small increase in short term PM(2.5).