In the present study, we have assessed population-based incidences and 30-days mortality of CAP among people 65 years or older in a well defined geographic area on the Mediterranean Coast of Spain during a consecutive 40-month study period. To our knowledge, this is the first contemporary study to assess rates of both hospitalised and outpatient CAP specifically focused on community-dwelling elderly people in a European country.
We have found that the incidence of CAP in our population (14 episodes per 1,000 elderly person-year) is more than three-folds higher than incidences previously reported in other Mediterranean regions[8, 10–12] and it is more similar to CAP incidences reported in Northern Europe or North America for elderly population groups [7, 9, 14, 15].
In Europe, in those population-based studies that evaluated the incidence of CAP in the general adult population, the reported incidence rates of CAP among the subgroup of people aged 65 years or older varied widely from 2 cases per 1,000 elderly person-year in Spanish individuals to 24 cases per 1,000 reported among Finnish elderly people . In three different regions along the Spanish Mediterranean Coast, the reported incidences of overall CAP have ranged from 1.2 to 1.8 cases per 1,000 all-age adult population (2.3 to 3.8 cases per 1,000 among people 65 years or older) [8, 10, 11] Incidence rates of 1.7 and 3.3 episodes of CAP per 1,000 person-year have been recently reported among Italian all-age adults and elderly individuals, respectively .
If we compare our results with those recently reported by Jackson et al in a population-based cohort study that evaluated the incidence of CAP among 46,237 elderly individuals in Washington State between 1998–2001, we can observe similar incidence rates of CAP requiring hospitalisation (10.5 per 1,000 in this study vs 11.5 per 1,000 in the Jackson's report). In contrast, the incidence of outpatient CAP was largely higher in USA elderly than in the present study (16.8 vs 3.5 cases per 1,000 person-year), which probably reflects differences in the definition criteria and management of outpatient CAP in both studies. In the present study (excluding three CAP cases who died in the emergency room before their possible hospitalisation), 15.5% of hospitalised CAP and 1.7% of outpatient CAP died within 30 days after the diagnosis, while in Jackson's report these percentages were 12.5% and 0.4% respectively. Overall, 4% of all the deaths in the cohort during the study period occurred within 30 days after a CAP diagnosis in this study versus 3.6% in Jackson's report.
In this study, incidence of CAP increased dramatically with ageing, achieving the highest rate in people aged 85 years or more, where 29 cases per 1,000 person-year were observed. According to sex and age strata, very elderly men are at the greatest risk considering that one episode of CAP can be expected every year for every 25 men aged 85 years or older. Similar trends in the incidence rates stratified by age have been reported in most prior epidemiological studies, considering that the frequent association between increasing age and presence of underlying diseases accounts for an increased morbid-mortality due to CAP in the oldest adults [17, 18, 21]. It must also be noted that in this study the 30-days case-fatality rate was three fold higher among patients 85 years or older than in patients 65–74 years, which supports the important specific role of age as a predictor of 30-days mortality among patients with CAP, as the pneumonia severity score reflects .
In the present study, the high rate of hospital admission may be explained by the characteristics of the study cohort (mean age: 75 years) and the characteristics of the "Tarragona region" where the study was conducted, particularly in relation to the easy accessibility to the reference hospital so that many patients sought medical care directly from the emergency service of the hospital rather than visiting a primary care physician. Interestingly, although the proportion of hospitalised cases was high in the present study, the incidence rate of CAP requiring hospitalisation resembles the rates reported in population-based studies conducted in the USA, where figures between 10.1 and 11.5 per 1,000 elderly person-year have been reported [9, 14].