Rising incidence and persistently high mortality of hospitalized pneumonia: a 10-year population-based study in Denmark

Background Little is known about temporal trends in the incidence and mortality of pneumonia in the general population. Methods We conducted a population-based cohort study in three Danish counties (population 1.4 million) to examine changes in the incidence and 30- and 90-day mortality associated with hospitalized pneumonia between 1994 and 2004. All adults hospitalized with a first-time diagnosis of pneumonia (n = 41 793) were identified in hospital discharge registries and followed for mortality through the Danish Civil Registry System. We determined age-standardized incidence rates and adjusted mortality rates associated with calendar year, gender, age and comorbidity. Results Between 1994 and 2003, the incidence of hospitalized pneumonia amongst adults increased from 288 per 100 000 person-years to 442 per 100 000 person-years, equivalent to an age-standardized incidence rate ratio of 1.50. The cumulative mortality within 30 and 90 days of admission was 15.2% and 21.9%, respectively, ranging from a 90-day mortality of 2.5% in patients aged 15-39 years to 34.7% in those aged 80 and over. Advanced age was the most important poor prognostic factor, followed by a high comorbidity score and male gender. The adjusted mortality rate ratios amongst patients with hospitalized pneumonia in 1999-2004, when compared with 1994-1998, were 0.89 (95% CI 0.85-0.94) after 30 days and 0.91 (95% CI 0.88-0.95) after 90 days. Conclusions The incidence of hospitalized pneumonia in Denmark has increased considerably during the last 10 years and, combined with persistently high mortality rates, is of clinical and public health concern.