Patient Demographic and Clinical Characteristics
After applying all inclusion and exclusion criteria, there were 27,659 patients who experienced 28,575 CAP episodes (Fig. 1). The vast majority of patients (97 %) had only one episode during the CAP identification period.
Of the 28,575 CAP episodes, 28 % were treated in an inpatient setting and 72 % were treated in an outpatient setting. Across both treatment settings, the mean age of patients with a CAP episode was 62.6 [SD 10.1] years, with both genders represented equally (Table 1). Among the inpatient CAP episodes, chronic obstructive pulmonary disease was the most common (36 %) chronic condition represented; among outpatient CAP episodes, diabetes was the most prevalent chronic condition (15.3 %). Across both treatment settings, 44.4 % of the total episodes occurred in patients categorized as low-risk who did not have traditional risk factors for CAP; however, the proportion of CAP episodes occurring in low-risk patients varied by treatment setting, with 55.0 % of the outpatient CAP episodes and only 17.7 % of inpatient episodes occurring in low-risk patients.
Length of CAP Episode and Inpatient Stay
Overall, the mean CAP episode length was 31.8 [SD 47.6] days for an inpatient episode and 10.2 [SD 23.7] days for an outpatient episode (Fig. 2). In general, the episode length increased with increasing age, reaching approximately 35 and 14 days for inpatient and outpatient episodes, respectively, for patients aged ≥75 years. The episode length also increased with higher risk. For inpatient episodes among patients aged ≥50 years, the mean [SD] episode length was 24.7 [30.4], 30.5 [46.6], and 39.5 [57.3] days for the low-, moderate-, and high-risk groups, respectively. The median episode length was much lower: 14 days for an inpatient episode and 1 day for an outpatient episode. This suggests that over half of the outpatient episodes involved only one healthcare encounter.
Overall, the mean number of inpatient stays for a CAP episode was 1.09 for patients ≥50 years of age. The overall mean length of stay, which may have included any re-hospitalization during the CAP episode, was 7.1 days. The length of stay increased with increasing levels of risk, with a mean of 4.8, 6.8, and 9.5 days for the low-, moderate-, and high-risk groups, respectively, for patients aged ≥50 years.
All-Cause Healthcare Costs
The overall mean cost for an outpatient episode was $2,212, but it was substantially higher for an inpatient episode ($27,661) (Fig. 3). For most age and risk groups, the cost of an outpatient episode was about one-tenth to one-eighth of the cost of an inpatient episode. As expected, the cost of an episode rose with increasing risk within an age group. However, even in the aged 50–64 years low-risk group, the mean cost to treat CAP in a hospital setting was high at $15,385 (Table 2). The median cost was much lower ($9,380), suggesting a skewed cost distribution. For both outpatient and inpatient CAP episodes, there was a wider range of mean costs across risk strata than across age groups.
For outpatient episodes, the majority of costs were due to ambulatory visits and other medical costs, which include non-pneumonia-related inpatient costs (Fig. 3). Pharmacy costs comprised only 9.7 % of outpatient episode costs. For inpatient episodes, 85.1 % of the all-cause costs were due to inpatient care.
CAP-Related Healthcare Costs
CAP-related healthcare costs represented 93.2, 90.0, and 81.4 % of the all-cause total healthcare costs for inpatient episodes for low-, moderate-, and high-risk patients aged ≥50 years, respectively. For outpatient episodes, CAP-related costs represented 55.7, 41.2, and 28.3 % of all-cause total healthcare costs incurred by low-, moderate-, and high-risk patients, respectively.