Overall, 3415 patients (median age 75 years) were admitted to hospital with community acquired pneumonia; 53% were men, and 10% (n=325) used a statin (table 1). Overall, 62% of the patients (n=2128) were categorised as high risk groups (class IV or V) according to the pneumonia severity index.
Characteristics of 3415 patients admitted to hospital with community acquired pneumonia, stratified by statin use
Statin users were older and more likely to have atherosclerosis related comorbidities. They still seemed to be healthy users, however, as they were more likely to be admitted from their homes, had independent mobility, were former smokers, were up to date with vaccinations, and had less need for an advanced directive (table 1). These findings were confirmed by the propensity score analysis, which included these variables among others (C-statistic 0.91). Rates of statin use increased across fifths of increasing propensity score: 1%, 3%, 5%, 12%, and 27% (P<0.001 for trend). Across these same fifths (representing increasing predicted probability of statin use), rates of in-hospital mortality or admission to an intensive care unit progressively decreased: 21%, 21%, 18%, 18%, and 14% (P=0.003 for trend).
Overall, 334 (10%) patients died in hospital, 351 (10%) were admitted to an intensive care unit, and 624 (18%) achieved the composite end point of death or admission to an intensive care unit. In univariate analyses, patients who used statins were less likely to die than non-users (25/325 (8%) v 309/3090 (10%), odds ratio 0.75, P=0.18), less likely to be admitted to an intensive care unit (29/325 (9%) v 322/3090 (10%), odds ratio 0.84, P=0.39), and less likely to achieve the composite outcome of death or admission to an intensive care unit (50/325 (15%) v 574/3090 (19%), odds ratio 0.80, P=0.15). All three univariate analyses suggest a clinically important benefit, and the composite outcome reached marginal statistical significance.
By constructing multivariate models with incrementally greater discriminatory power, the adjusted odds ratio for statin use and adverse outcomes increased from 0.78 (adjusted for age and sex, 95% confidence interval 0.57 to 1.07, P=0.12) to 0.88 (typical adjustments in administrative databases including age, sex, nursing home resident, comorbidities, and number of drugs, 0.63 to 1.22, P=0.43) and to 1.07 (all previous variables plus clinical data, including former smoker, independent mobility, immunisations, and pneumonia severity class, 0.75 to 1.52, P=0.73; figure). Inclusion of the propensity score as a continuous variable in this last model further moved the estimates in the direction of harm (adjusted odds ratio 1.12, 95% confidence interval 0.77 to 1.64, P=0.55). A model including only the propensity score gave an estimate of effect for statin use of 1.01 (0.72 to 1.41, P=0.95).
Odds ratios (95% confidence intervals) for association between statin use and death or admission to an intensive care unit in patients with community acquired pneumonia in models with progressively more complete multivariate adjustment (more ...)
Finally, the best multivariate model of adverse community acquired pneumonia related outcomes was constructed in which only age, propensity score, and statin use was forced. This last model had a C-statistic of 0.84 (table 2); the estimate of statin effect was 1.10 (95% confidence interval 0.76 to 1.60, P=0.61). Models that considered in-hospital mortality only or admission to an intensive care unit only produced virtually identical results with two notable exceptions: older age and heart disease significantly increased risk of mortality (adjusted odds ratio 2.10 and 1.11) but significantly “protected” against admission to an intensive care unit (0.44 and 0.21). When these end points were pooled, counter intuitively, older age and heart disease seemed to reduce the risk of adverse events related to community acquired pneumonia (table 2). In no adjusted models, however, did statin use have a statistically significant effect or point estimate consistent with benefit (data not shown).
Multivariate logistic regression analysis of correlates for mortality or admission to an intensive care unit in 3415 patients admitted to hospital with community acquired pneumonia