Diagnoses of early and late readmissions after hospitalization for pneumonia. A systematic review.

RATIONALE: Pneumonia is a frequent cause of hospitalization, yet drivers of post-pneumonia morbidity remain poorly characterized. Causes of hospital readmissions may elucidate important sources of morbidity and are of particular interest given the U.S. Hospital Readmission Reductions Program.
OBJECTIVES: To review the primary diagnoses of early (≤30 d) and late (≥31 d) readmissions after pneumonia hospitalization.
METHODS: Systematic review of MEDLINE, Embase, and CINAHL databases. We identified original research studies of adults aged 18 years or older, hospitalized for pneumonia, and for whom cause-specific readmission rates were reported. Two authors abstracted study results and assessed study quality.
MEASUREMENTS AND MAIN RESULTS: Of the 1,243 citations identified, 12 met eligibility criteria. Included studies were conducted in the United States, Spain, Canada, Croatia, and Sweden. All-cause 30-day readmission rates ranged from 16.8 to 20.1% across administrative studies; the weighted average for the studies using chart review was 11.6% (15.6% in United States-based studies). Pneumonia, heart failure/cardiovascular causes, and chronic obstructive pulmonary disease/pulmonary causes are the most common reasons for early readmission after pneumonia hospitalization. Although it was the single most common cause for readmission, pneumonia accounted for only 17.9 to 29.4% of all 30-day readmissions in administrative studies and a weighted average of 23.0% in chart review studies. After accounting for study population, there was no clear difference in findings between claims-based versus chart-review studies. Few studies assessed readmissions beyond 30 days, although the limited available data suggest similar primary diagnoses for early and late readmissions. No studies assessed whether reasons for readmission were similar to patients' reasons for healthcare use before hospitalization.
CONCLUSIONS: Pneumonia, heart failure/cardiovascular disease, and chronic obstructive pulmonary disease/pulmonary disease are the most common readmission diagnoses after pneumonia hospitalization. Although pneumonia was the most common readmission diagnosis, it accounted for only a minority of all readmissions. Late readmission diagnoses are less thoroughly described, and further research is needed to understand how hospitalization for pneumonia fits within the broader context of patients' health trajectory.