The emerging role of atypical pathogens in community-acquired pneumonia

Prevalence of Pulmonary Infections Caused by Atypical Pathogens in non-HIV Immunocompromised Patients

Although atypical bacteria are important causes of lower airway infections, data on their role in immunocompromised patients are scarce. The aim of the study was to evaluate the prevalence of atypical pulmonary infections in patients with various types of immunosuppression, and to analyze clinical characteristics of these infections. Eighty non-HIV immunocompromised patients with different underlying diseases and clinical and radiological signs of pulmonary infection were enrolled. Due to incomplete data on eight patients, 72 patients were eligible for final analysis (median age 58 years). All patients underwent fiberoptic bronchoscopy and bronchoalveolar lavage. Bronchoalveolar lavage fluid (BALF) fluid samples were sent for direct microscopy, cultures, and fungal antigen detection, when appropriate. Commercial qualitative amplification assay (PNEUMOTRIS oligomix Alert Kit(®)), based on nested PCR method, was used to detect specific DNA sequences of L. pneumophila, C. pneumoniae, and M. pneumoniae in BALF. There were 61 (84.7 %) patients with hematologic diseases, 3 (4.2 %) after solid organ transplantation, and 8 (11.1 %) with miscellaneous diseases affecting immune status. Specific sequences of M. pneumoniae, C. pneumoniae, and L. pneumophila DNA were found in 7 (9.7 %), 2 (2.8 %), and 0 patients, respectively. In 8 of these patients co-infections with different microorganisms were demonstrated. Co-infection with A. baumanii and P. aeruginosa was diagnosed in three patients who died. We conclude that atypical lower airway infections are uncommon in immunocompromised patients. The majority of these infections are co-infections rather than single pathogen infections.

Polymicrobial community-acquired pneumonia: An emerging entity

Polymicrobial aetiology in community-acquired pneumonia (CAP) is more common than previously recognized. This growing new entity can influence inflammation, host immunity and disease outcomes in CAP patients. However, the true incidence is complicated to determine and probably underestimated due mainly to many cases going undetected, particularly in the outpatient setting, as the diagnostic yield is restricted by the sensitivity of currently available microbiologic tests and the ability to get certain types of clinical specimens. The observed rate of polymicrobial cases may also lead to new antibiotic therapy considerations. In this review, we discuss the pathogenesis, microbial interactions in pneumonia, epidemiology, biomarkers and antibiotic therapy for polymicrobial CAP.

Mixed community-acquired lower respiratory tract infections

Although mixed infections are known to be clinically relevant in conditions such as nosocomial pneumonia and ventilator-related pneumonia, it is increasingly recognized that a substantial number of community-acquired lower respiratory tract infections may also be attributed to more than one pathogenic organism. A better definition of the true incidence of mixed infections in community-acquired lower respiratory tract infections is partly derived from recent advances in available diagnostic methods (eg, molecular biology). Two points still must be determined: whether the presence of a mixed infection is associated with altered outcomes and whether empirical antibiotic selection should be modified to account for potential polymicrobial infections.

Clinical and bacteriological outcomes in hospitalised patients with community-acquired pneumonia treated with azithromycin plus ceftriaxone, or ceftriaxone plus clarithromycin or erythromycin: a prospective, randomised, multicentre study

This study compared patients with moderate-to-severe community-acquired pneumonia (CAP) requiring hospitalisation, who received initial therapy with either intravenous ceftriaxone plus intravenous azithromycin, followed by step-down to oral azithromycin (n = 135), with patients who received intravenous ceftriaxone combined with either intravenous clarithromycin or erythromycin, followed by step-down to either oral clarithromycin or erythromycin (n = 143). Clinical and bacteriological outcomes were evaluated at the end of therapy (EOT; day 12-16) or at the end of study (EOS; day 28-35). At baseline, mean APACHE II scores were 13.3 and 12.6, respectively, with >50% of patients classified as Fine Pneumonia Severity Index (PSI) category IV or V. Clinical success rates (cure or improvement) in the modified intent-to-treat (MITT) population at EOT were 84.3% in the ceftriaxone/azithromycin group and 82.7% in the ceftriaxone/clarithromycin or erythromycin group. At EOS, MITT success rates (cure only) were 81.7% and 75.0%, respectively. Equivalent success rates in the clinically evaluable population were 83% and 87%, respectively, at EOT, and 79% and 78%, respectively, at EOS. MITT bacteriological eradication rates were 73.2% and 67.4%, respectively, at EOT, and 68.3% vs. 60.9%, respectively, at EOS. Mean length of hospital stay (LOS) was 10.7 and 12.6 days, and the mean duration of therapy was 9.5 and 10.5 days, respectively. The incidence of infusion-related adverse events was 16.3% and 25.2% (p 0.04), respectively. An intravenous-to-oral regimen of ceftriaxone/azithromycin was at least equivalent in efficacy and safety to the comparator regimen and appeared to be a suitable treatment option for hospitalised patients with CAP.

Clinical characterisation of pneumonia caused by atypical pathogens combining classic and novel predictors

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.

PNEUMONIA | Atypical

‘Atypical pneumonia’ refers to a clinical syndrome associated with pneumonia (typically mild, nonlobar) and diverse upper respiratory tract and extrapulmonary manifestations. Clinical features overlap with bacterial pneumonia, and co-infection with both typical (e.g., Streptococcus pneumoniae or other bacteria) and atypical pathogens may occur. ‘Atypical’ pathogens include Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella spp. In large epidemiological studies, Mycoplasma pneumoniae has been implicated in 2–18% of community-acquired pneumonias; Chlamydia pneumoniae, in 2–8%; Legionella sp., 1–4%. Atypical pathogens lack cell walls and are resistant to β-lactam antibiotics but are usually susceptible to tetracyclines, macrolides, ketolides, and fluoroquinolone antibiotics. In this article, we also review other unusual causes of pneumonia which are transmitted by insects or vectors (e.g., Rocky Mountain spotted fever, cat scratch fever, Q fever, ehrlichiosis, Lyme disease, and tularemia). These diverse organisms are not found on Gram stain, and diagnosis requires special culture techniques or serological assays. We review the salient clinical and laboratory features of these various disorders, and discuss diagnostic and therapeutic strategies.

Epidemiology of community-acquired pneumonia in adult patients at the dawn of the 21st century: a prospective study on the Mediterranean coast of Spain

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 of mixed etiology: prevalence, clinical characteristics, and outcome

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.

Increased Antibiotic Resistance in Respiratory Tract Pathogens: PROTEKT US—An Update

Three major North American surveillance programs have tracked antimicrobial resistance patterns among isolates of Streptococcus pneumoniae and other common respiratory tract pathogens. The Canadian Bacterial Surveillance Network shows the progressive increase in resistance among pneumococcal S. pneumoniae to penicillin, trimethoprim-sulfamethoxazole, macrolides, and fluoroquinolones. The data from the Tracking Resistance in the United States Today study also show a steady rise in pneumococcal resistance among common antibiotics as well as an increase in multidrug-resistant S. pneumoniae. The US component of the Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin study has detected increasing resistance to many antimicrobial agents among common respiratory isolates, with marked geographic variations in resistance patterns. The patterns of resistance detected by these major surveillance programs are a warning signal regarding the continued emergence of resistance among community-acquired respiratory tract pathogens.

Antibacterial resistance among children with community-acquired respiratory tract infections (PROTEKT 1999-2000)

OBJECTIVE

To determine the susceptibility of bacterial respiratory tract pathogens, isolated from children (0-12 years) as part of the global PROTEKT surveillance study (1999-2000), to a range of antibacterials, including the ketolide telithromycin.

METHODS

Minimum inhibitory concentrations of the antibacterials studied were determined at a central laboratory using the NCCLS microdilution broth method. Macrolide resistance mechanisms were detected by PCR.

RESULTS

Of 779 Streptococcus pneumoniae isolates worldwide, 43% were non-susceptible to penicillin (18% intermediate; 25% resistant) and 37% were resistant to erythromycin, with considerable intercountry variation. Eighteen per cent of 653 Haemophilus influenzae and >90% of 316 Moraxella catarrhalis isolates produced beta-lactamase. Of 640 Streptococcus pyogenes isolates, 10% were resistant to erythromycin, with considerable intercountry variation. All S. pneumoniae and 99.8% of H. influenzae isolates were susceptible to telithromycin using breakpoints proposed to the NCCLS (<or=1 and <or=4 mg/L, respectively). All M. catarrhalis and 97% of S. pyogenes and isolates were susceptible to <or=1 mg/L telithromycin.

CONCLUSIONS

Antibacterial resistance complicates the empirical treatment of respiratory tract infections in children and requires continued monitoring. Telithromycin may be a useful therapeutic alternative as it is highly active against strains exhibiting various resistance phenotypes.

Management of community-acquired pneumonia: a focus on conversion from hospital to the ambulatory setting

Patients with community-acquired pneumonia (CAP) are treated in hospital or in the ambulatory care setting depending on the severity of illness. Despite numerous guidelines proposed, there is no agreement on specific criteria for hospitalization other than the clinicians' experience. The purpose of this review is to discuss the importance of the appropriate choice and timely administration of antibacterial agents, either in the hospital or in the outpatient setting. Since a high proportion of CAP patients will not have an etiologic agent identified at the time of initiation of treatment, the choice of antibacterial therapy is usually empiric. Antibacterial agents with activity against pneumococci and atypical pathogens causing pneumonia are the preferred choices. Macrolides, doxycycline, or respiratory fluoroquinolones have been recommended by various guidelines committees in North America for the treatment of pneumonia in patients with or without underlying comorbidities. Because of the increasing resistance to beta-lactams as well other antibacterial agents such as macrolides, doxycycline, and sulfamethoxazole/trimethoprim (cotrimoxazole), it is important that clinicians are aware of local statistics on resistance to Streptococcus pneumoniae, as infection with this bacterium is associated with high rates of morbidity and mortality. More recently, fluoroquinolone resistance has been reported, but the percentage of pneumococcal strains resistant to this agent is relatively low compared with the other antibacterial agents. Switch (intravenous to oral) therapy is recommended for hospitalized patients with CAP to facilitate early discharge, which has been shown to improve patient satisfaction and reduce hospital costs. Early conversion to oral therapy has not been shown to be associated with increased complications or higher mortality. Following prompt intravenous therapy and stabilization, patients with CAP should be treated with oral therapy in the ambulatory setting.

The role of infection in the pathogenesis of cardiovascular disease

Atherosclerosis is a complex, multifactorial disease. Recently, research has intensified to identify the role of various infections in the pathogenesis of atherosclerosis. Specific agents have been proposed as direct initiators or accelerators of atherosclerosis, while other infectious agents have been proposed as accelerators of atherosclerosis through nonspecific stimulation of the inflammatory cascade. Recently, the total pathogen burden concept has suggested that while each specific infection contributes only slightly to the pathogenesis of atherosclerosis, the cumulative effects of infectious agents contribute greatly. Several randomized trials evaluating antibiotic therapy in the prevention of cardiovascular events have now been completed, although results have been conflicting. This manuscript summarizes current understanding of the role of infectious agents as a trigger of inflammation, as a contributor to atherosclerosis, and the potential role of antibiotic therapy in the treatment of atherosclerosis.

Community-acquired pneumonia in the emergency department: a practical approach to diagnosis and management

Pneumonia is one of the most common conditions for which patients seek emergency care. It is a challenging infection in that the spectrum of illness ranges from the nontoxic patient appropriate for outpatient antibiotics to the critically ill patient requiring intensive care hospitalization. Current data and diagnostic technology provide the emergency physician with the tools for an appropriately rapid evaluation and consideration of the differential diagnosis. Key critical thinking and application of published findings allow for intelligent empirical antibiotic treatment and risk stratification for the best disposition. Although antibiotic-resistant organisms increasingly are being identified, patients continue to benefit from early institution of standard ED treatment. Coverage for atypical organisms improves patient response and outcome. Finally, identification and treatment of the complications of pneumonia and accompanying sepsis must be considered by the ED physician when evaluating critically ill patients.