The prevalence of community-acquired pneumonia (CAP) due to Pseudomonas aeruginosa (PA) is low, according to the results of a study published in the Annals of the American Thoracic Society. The investigators also identified differences between the clinical features and 30-day mortality rates of patients with indeterminate and determinate PA pneumonia.

This study aimed to identify the prevalence of both indeterminate and determinate PA pneumonia infections, describe the clinical and microbiologic profiles, and estimate the costs of unnecessary prescriptions. To do so, 2701 patients with CAP were prospectively enrolled from 2 Japanese hospitals and categorized as having definitive PA, indeterminate PA, and non-PA pneumonia.

A total of 156 cases of PA pneumonia were isolated; 25 (0.9%) were definitive and 131 (4.9%) were indeterminate. Factors more likely to be associated with definitive PA pneumonia were a history of tuberculosis and chronic obstructive pulmonary disease/bronchiectasis. The investigators also noted considerable clinical differences among patients with indeterminate PA pneumonia vs those with non-PA pneumonia. The following factors were associated with indeterminate PA pneumonia: nursing home residence; oral steroid treatment; neuromuscular disease; low body mass index; hospitalization during the prior 90 days; history of pneumonia; vital sign abnormality; hypoalbuminemia; and assistance needed with daily activities. Those with indeterminate PA pneumonia were, however, less likely than patients with non-PA pneumonia to have hypertension.


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Case fatality rates among patients with definitive PA pneumonia at Day 14 and Day 30 were 24% and 28%, respectively, and differed significantly from the 14- and 30-day rates for patients with non-PA pneumonia (4% and 5%, respectively). Case fatality rates for those with indeterminate PA pneumonia were similar to those for patients with non-PA pneumonia.

Higher proportions of patients with definitive and indeterminate PA pneumonia were initially treated with antipseudomonal drugs (80% and 58%, respectively). Overall, 27.4% of the 2701 patients in the study were prescribed antipseudomonal drugs. Of these, 2.7% had definitive PA pneumonia, resulting in the remainder (97.3%) potentially receiving unnecessary treatment. Drug resistance was documented in 4 patients with definitive PA and 8 with indeterminate PA. None of the definitive PA resistance cases were multidrug-resistant PA; 4 cases of drug resistance occurred among the patients with indeterminate PA, and 1 indeterminate PA case showed carbapenem resistance.

This study was limited in that it included patients from 2 hospitals and lacked the standardized criteria for defining definitive and indeterminate PA. In addition, the low sample size meant that 95% confidence intervals from the regression analysis of associated clinical factors should be interpreted with caution.

The investigators concluded that the prevalence of definitive PA among patients with CAP is low, and clinical features and outcomes across the 3 PA categories were different. Therefore, the investigators recommend that risk factors for PA pneumonia be specified only for definitive PA cases and that proportions of both types be locally validated. The investigators also stressed the importance of stringent criteria for CAP diagnosis in order to avoid unnecessary treatment with antipseudomonal agents.

Reference

Sando E, Suzuki M, Ishida M, et al. Definitive and indeterminate Pseudomonas aeruginosa infection in adults with community-acquired pneumonia: a prospective observational study. Ann Am Thorac Soc. Published online February 10, 2021. doi:10.1513/AnnalsATS.201906-459OC