The aim of this study was to characterise community-acquired pneumonia (CAP) caused by atypical pathogens by combining distinctive clinical and epidemiological features and novel biological markers. A population-based prospective study of consecutive patients with CAP included investigation of biomarkers of bacterial infection, e.g., procalcitonin, C-reactive protein and lipopolysaccharide-binding protein (LBP) levels. Clinical, radiological and laboratory data for patients with CAP caused by atypical pathogens were compared by univariate and multivariate analysis with data for patients with typical pathogens and patients from whom no organisms were identified. Two predictive scoring models were developed with the most discriminatory variables from multivariate analysis. Of 493 patients, 94 had CAP caused by atypical pathogens. According to multivariate analysis, patients with atypical pneumonia were more likely to have normal white blood cell counts, have repetitive air-conditioning exposure, be aged <65 years, have elevated aspartate aminotransferase levels, have been exposed to birds, and have lower serum levels of LBP. Two different scoring systems were developed that predicted atypical pathogens with sensitivities of 35.2% and 48.8%, and specificities of 93% and 91%, respectively. The combination of selected patient characteristics and laboratory data identified up to half of the cases of atypical pneumonia with high specificity, which should help clinicians to optimise initial empirical therapy for CAP.

This study presents data from a prospective study of adult patients with community-acquired pneumonia (CAP). Of 493 patients included in the study, 223 (45.2%) were aged > or = 65 years, and 265 (53.7%) had one or more underlying diseases, mostly chronic obstructive pulmonary disease, diabetes mellitus or dementia. In total, 281 microorganisms were identified in 250 (50.7%) patients, with two or more pathogens detected in 28 (5.7%) cases. Microbial diagnosis varied according to age, severity, co-morbidity and site-of-care, but there was much overlap among groups. Streptococcus pneumoniae was the single most prevalent organism in outpatients, patients admitted to hospital, and patients who died, either as a single pathogen or combined with another organism. Infections caused by 'atypical' pathogens were seen across all groups, including the elderly and patients with co-morbidities. Mortality varied according to the pneumonia severity index (PSI) of the pneumonia patient outcomes research team. Shock (OR 34.48), an age of > 65 years (OR 25) and altered mental status (OR 9.92) were factors associated independently with 30-day mortality. Key findings from this study were the advanced age of the population with CAP, and the high prevalence of dementia as an underlying disease. The study also revealed that microbiological diagnosis of CAP remains problematic. Although certain epidemiological features may help to predict the microbial aetiology, the overlap among groups reduces the usefulness of this information in guiding therapeutic decisions. Greater effort should be made to improve identification methods for microbial pathogens causing CAP.

Community-acquired pneumonia (CAP) of mixed etiology has increasingly been appreciated in the literature, but its clinical significance remains unknown. The aim of this analysis was to describe the prevalence, clinical characteristics, and outcome of CAP of mixed etiology. Data were obtained from a 2-year prospective study of consecutive patients with CAP in whom an extensive microbiological workup was performed. Predefined strict criteria were used to establish the etiology. A total of 493 patients were included. A single pathogen was detected in 222 (45%) cases and two or more pathogens in 28 (5.7%) cases. Mixed infections were seen across all age groups and in patients treated both in hospital and as outpatients. The most frequent combinations of pathogens were those of a bacterium plus an “atypical” organism (28.6%) and of two bacterial organisms (28.6%). Compared with patients with monomicrobial pneumonia, patients with mixed pneumonia were more likely to have underlying conditions (64% vs. 45%, p=0.04) and dementia (25% vs. 10%, p=0.02). The incidence of a defined series of complications was higher in patients with mixed pneumonia (39.3% vs. 18.6%; OR=2.84; p=0.02). Community-acquired pneumonia of mixed etiology is uncommon. Patients with mixed pneumonia are more likely to have underlying medical conditions, and they may have a more severe course of disease.

Community-acquired pneumonia (CAP) is a major cause of morbidity and mortality. However, identification of the infecting organism is achievable in only 40–50% of cases, and results are not usually available when the diagnosis of pneumonia is first established (1)(2). Therefore, initial therapy is typically empirical, usually aimed at the standard bacteria, most commonly Streptococcus pneumoniae , and “atypical” pathogens (e.g., Mycoplasma pneumoniae , Legionella species, Chlamydophilia species, and Coxiella burnetii ) that have long been considered the most frequent causes of CAP. Given their effectiveness against S. pneumoniae as well as atypical organisms, macrolide antibiotics have been widely used as initial monotherapy in many cases of CAP. The selection of empirical therapy has become complicated by the emergence of drug-resistant S. pneumoniae , including a growing number of strains resistant to macrolides (1)(2)(3). In light of these uncertainties, clinicians may be inclined to prescribe broad-spectrum antimicrobial coverage for many patients with CAP, a practice that could lead to increasing bacterial resistance over the next few years (3). A patient-specific therapy for CAP that relies on antibiotics with a focused spectrum of activity could improve the care of the individual patient and prevent antibiotic abuse, reducing the risk of microorganisms becoming drug resistant. Therefore, the development of biomarkers to help clinicians predict the microbial etiology of CAP could be useful for selecting patient populations in which this strategy may be appropriate and effective. In fact, a therapeutic strategy based on the concentration of procalcitonin (PCT), a marker of bacterial infection, has recently demonstrated usefulness in reducing antibiotic overuse in lower respiratory tract infections (4). Lipopolysaccharide-binding protein (LBP) is the principal plasma protein responsible for transporting endotoxin molecules to immune effector cells bearing CD14 on their surface (5). High serum LBP concentrations have been found …

We evaluated the Binax NOW rapid immunochromatographic membrane test (ICT) for detection of Streptococcus pneumoniae urinary antigen in a population-based prospective study of adults with community-acquired pneumonia (CAP). ICT was performed with urine samples obtained from 452 (91.7%) of 493 patients enrolled. Pneumococcal antigen was detected in 19 (70.4%) of 27 patients with pneumococcal pneumonia. The test results were more frequently positive for patients who had not received antibiotics before testing (26.6% vs. 12.1%; P=.002). Only 16 (10.3%) of 156 samples obtained from patients with nonpneumococcal pneumonia yielded a positive result. Of the 269 patients who had pneumonia with no pathogen identified, antigen was detected in 69 (25.7%). With conventional microbiological criteria used as the "gold standard," the test had a sensitivity of 70.4% and a specificity of 89.7%. Testing concentrated urine samples with the ICT may be a useful technique for rapid diagnosis of pneumococcal pneumonia in adults with CAP.