Mortality reduction among pneumonia patients still substantial despite the impact of coding changes

Accounting for changes in coding practices may be important in analyzing trends based on administrative data. Several studies have demonstrated large reductions in mortality over time among pneumonia patients. However, a recent study suggested that this reduction may have been an artifact of case definition because more of the highest-risk patients were being coded under alternative principal diagnoses in recent years.

Using the National Inpatient Sample from 1993 to 2005, we selected hospitalizations with a principal diagnosis of pneumonia or a secondary diagnosis of pneumonia and a principal diagnosis of sepsis or respiratory failure. We performed logistic regression, estimating the likelihood of in-hospital mortality in each year, adjusting for age, sex, and comorbidities.

Over time, there was a substantial increase in the frequency of sepsis and respiratory failure as a principal diagnosis. Length of stay decreased in all 3 principal diagnosis groups. By 2005, the adjusted odds ratio (OR) of death among principal diagnosis pneumonia and respiratory failure hospitalizations decreased to 0.50 (95% confidence interval [CI], 0.49-0.51) and 0.62 (95% CI, 0.58-0.66), respectively, compared with 1993. With all 3 groups combined, there was still a substantial, albeit attenuated, reduction in the risk of mortality (OR(2005) 0.70; 95% CI, 0.69-0.72).

Survival of patients with community-acquired pneumonia has improved greatly over time. However, interpretation of such findings based on administrative data must be made with caution and careful attention to case definition and coding trends.