Legionella and community-acquired pneumonia: a review of current diagnostic tests from a clinician's viewpoint

Community-acquired pneumonia by Legionella pneumophila serogroups 1–6 in Brazil

A prospective cohort study of adult patients hospitalized due to community-acquired pneumonia was carried out for 1 year in a Brazilian university general hospital to detect the incidence of community-acquired pneumonia by Legionella pneumophila serogroups 1-6. During a whole year, a total of 645 consecutive patients who were hospitalized due to a initial presumptive diagnosis of respiratory disease by ICD-10 (J00-J99), excluding upper respiratory diseases, were screened to detect the patients with community-acquired pneumonia. Fifty-nine consecutive patients hospitalized due to community-acquired pneumonia between July 19, 2000 and July 18, 2001, were included in the study. They had determinations of serum antibodies to L. pneumophila serogroups 1-6 by indirect immunofluorescence antibody test at the Infectious Diseases Laboratory of University of Louisville (KY, USA) and urinary antigen tests for L. pneumophila serogroup 1. Three patients had community-acquired pneumonia by L. pneumophila serogroups 1-6, two patients being diagnosed by seroconversion and positive urinary antigen tests; the other had negative serologies but strongly positive urinary antigen test. The incidence of community-acquired pneumonia by L. pneumophila serogroups 1-6 in our hospital was 5.1%.

Value of intensive diagnostic microbiological investigation in low- and high-risk patients with community-acquired pneumonia

In a prospective study to evaluate the diagnostic yield of different microbiological tests in hospitalised patients with community-acquired pneumonia, material for microbiological investigation was obtained from 262 patients. Clinical samples consisted of the following: sputum for Gram staining, culture, and detection of pneumococcal antigen; blood for culture and serological tests; urine for detection of Legionella pneumophila serogroup 1 antigen and pneumococcal antigen; and specimens obtained by fiberoptic bronchoscopy. A pathogen was identified in 158 (60%) patients, with Streptococcus pneumoniae (n=97) being the most common causative agent of community-acquired pneumonia. In 82% of the 44 patients with an adequate sputum specimen, a positive Gram stain was confirmed by positive sputum culture. S. pneumoniae infections were detected principally when adequate sputum specimens were examined by Gram stain and culture and when adequate and inadequate sputum specimens were tested for the presence of pneumococcal antigen (n=58; 60%). The urinary pneumococcal antigen test was the most valuable single test for detection of S. pneumoniae infections (n=52; 54%) when sputum pneumococcal antigen determination was not performed. Fiberoptic bronchoscopy was of additive diagnostic value in 49% of the patients who did not expectorate sputum and in 52% of those in whom treatment failed. Investigation of sputum by a combination of Gram stain, culture, and detection of pneumococcal antigen was the most useful means of establishing an aetiological diagnosis of community-acquired pneumonia, followed by testing of urine for pneumococcal antigen. Fiberoptic bronchoscopy may be of additional value when treatment failure occurs.

Community-acquired pneumonia as the initial manifestation of serious underlying diseases

PURPOSE

Community-acquired pneumonia is common among patients with coexisting illnesses and it can be the initial manifestation of these comorbid diseases. The objectives of our study were to evaluate the frequency of this association and to analyze whether certain characteristics could predict the presence of unknown comorbid conditions.

SUBJECTS AND METHODS

Over a 5-year period, we prospectively studied 660 consecutive patients with community-acquired pneumonia seen at our institution. In a subgroup of these patients, diagnosis of previously unknown comorbid conditions was established during follow-up. Characteristics of these patients were compared with data from the remaining sample of patients.

RESULTS

Prior underlying diseases were present in 298 (45%) patients. One or more new comorbid conditions were found in 41 (6%), of which diabetes (14 cases), malignancies (12 cases), chronic obstructive pulmonary disease (8 cases), and human immunodeficiency virus (HIV) infection (5 cases) were the most common. In the comparative study, a bacterial etiology, positive blood cultures, and hospitalization were more frequently found (P < 0.05) in patients with new comorbid conditions than atypical microorganisms or viruses, negative blood cultures, or outpatient care.

CONCLUSION

In the initial diagnostic workup of patients with community-acquired pneumonia, the possibility of unknown comorbid conditions should be carefully evaluated.

Role of beta-lactam agents in the treatment of community-acquired pneumonia

Community-acquired pneumonia (CAP) is a common illness associated with high rates of morbidity and mortality worldwide. The beta-lactam antibacterial agents have been the mainstay of therapy for CAP for over four decades and remain as first-line therapy. However, the impact of the substantial prevalence of resistance seen among the common respiratory pathogens, particularly penicillin and macrolide resistance among Streptococcus pneumoniae, is now an area for concern. CAP treatment guidelines often recommend the use of a macrolide or fluoroquinolone in conjunction with, or as an alternative to, beta-lactam agents, but whether this is necessary is uncertain. This review outlines the historical use of beta-lactam antibacterial agents in the treatment of CAP along with their ongoing therapeutic utility.

[Guidelines for the management of community pneumonia in adult who needs hospitalization]

Community acquired pneumonia is still an important health problem. In Spain the year incidence is 162 cases per 100,000 inhabitants with 53,000 hospital admission costing 115 millions of euros per year. In the last years there have been significant advances in the knowledge of: aetiology, diagnostic tools, treatment alternatives and antibiotic resistance. The Spanish Societies of Intensive and Critical Care (SEMICYUC), Infectious Diseases and Clinical Microbiology (SEIMC) and Pulmonology and Thoracic Surgery (SEPAR) have produced these evidence-based Guidelines for the management of community acquired pneumonia in Adults. The main objective is to help physicians to make decisions about this disease. The different points that have been developed are: aetiology, diagnosis, treatment and prevention.

Bronchoalveolar lavage findings in severe community-acquired pneumonia due to Legionella pneumophila serogroup 1

BACKGROUND

No specific data are available in the literature on the bronchoalveolar Lavage (BAL) findings of Legionella pneumophila pneumonia. We report on the cytological and immunophenotypical BAL data of three immunocompetent patients with severe community-acquired pneumonia due to L. pneumophila serogroup 1.

METHODS

Retrospective chart review. The microbiologial diagnosis was obtained by BAL culture or/and urinary antigen assay.

RESULTS

All patients presented with high-grade fever, bilateral chest infiltrates and severe respiratory failure requiring ventilatory support. The cytological BAL pattern at presentation showed in all patients the association of a marked neutrophilia with a variable but remarkable percentage of lymphoblasts. Increased levels of activated T-Lymphocytes (both HLA-DR + and CD25 + cells) and, in 2 out of 3 patients, of T-cells bearing the gamma/delta T-cell receptor were the main immunophenotypical findings on flow cytometric analysis.

CONCLUSIONS

We suggest that the association of lymphoblasts with a marked neutrophilia in BAL fluid of patients with a clinical-radiological setting compatible with acute pneumonia should suggest L. pneumophila as a possible etiologic agent.

Impact of positive legionella urinary antigen test on patient management and improvement of antibiotic use

AIM

To assess the incidence of legionella infection over a 27 month period at a large university hospital.

MATERIAL AND METHODS

The present retrospective cohort study enrolled patients with legionellosis, defined as those presenting a positive urinary antigen for legionella together with a medical history, clinical findings, and radiological findings consistent with pneumonia. These patients were evaluated to determine the relation between their test results and changes in treatment modalities. A control group of patients with pneumonia but a negative urinary antigen test for legionella were also analysed.

RESULTS

Twenty seven of 792 assessed patients tested positive for legionella. In 22 of these patients, legionella active antibiotics were administered empirically. In seven patients, the test results prompted a legionella specific treatment, whereas in 12 cases, non-specific antibiotics were stopped within 24 hours. Overall, treatment was altered in more than half of the patients as a result of the test results.

CONCLUSIONS

The urinary antigen may have a direct impact on clinical management of pulmonary legionellosis. However, patient comorbidities and individual clinical judgment are still important for determining the best treatment to be given in each individual case.

Legionella pneumonia: infection during immunosuppressive therapy for idiopathic pulmonary hemosiderosis

We report a case of Legionella pneumonia in a 10-year-old girl with idiopathic pulmonary hemosiderosis who was chronically immunosuppressed and had exposure to a hot tub. Prompt diagnosis with bronchoalveolar lavage and subsequent antimicrobial therapy resulted in full recovery. Legionellosis should be included in the differential diagnosis of the immunosuppressed child with respiratory illness. High risk patients should avoid exposure to hot tubs.

El hospital ante un brote prolongado de legionelosis

OBJECTIVE

To describe the health resources used in patients hospitalized with Legionella pneumonia during an outbreak of Legionnaire's disease in Alcoy (Spain), and to compare them with those used in other forms of pneumonia.

METHODS AND RESULTS

Using a clinical protocol, 177 Legionella pneumonia patients were compared with 180 patients hospitalized for other types of pneumonia. Data on therapy and the resources used were collected. The most common antibiotic treatment in both groups was clarithromycin, but intensive care and mechanical ventilation requirements were greater in Legionella pneumonia. Home-based hospital care was successfully used in 15.6% of patients with Legionella pneumonia and in 11.3% of those with other types of pneumonia. Home oxygen therapy after discharge was less frequent in the Legionella pneumonia group (7.8%) than in the group with non-Legionella pneumonia (16.7%).

CONCLUSIONS

Notable results were the greater requirement for mechanical ventilation in Legionella pneumonia and the good results obtained by home-based hospital care within current health care management.

Community-acquired pneumonia

This seminar reviews important features and management issues of community-acquired pneumonia (CAP) that are especially relevant to immunocompetent adults in light of new information about cause, clinical course, diagnostic testing, treatment, and prevention. Streptococcus pneumoniae remains the most important pathogen; however, emerging resistance of this organism to antimicrobial agents has affected empirical treatment of CAP. Atypical pathogens have been quite commonly identified in several prospective studies. The clinical significance of these pathogens (with the exception of Legionella spp) is not clear, partly because of the lack of rapid, standardised tests. Diagnostic evaluation of CAP is important for appropriate assessment of severity of illness and for establishment of the causative agent in the disease. Until better rapid diagnostic methods are developed, most patients will be treated empirically. Antimicrobials continue to be the mainstay of treatment, and decisions about specific agents are guided by several considerations that include spectrum of activity, and pharmacokinetic and pharmacodynamic principles. Several factors have been shown to be associated with a beneficial clinical outcome in patients with CAP. These factors include administration of antimicrobials in a timely manner, choice of antibiotic therapy, and the use of a critical pneumonia pathway. The appropriate use of vaccines against pneumococcal disease and influenza should be encouraged. Several guidelines for management of CAP have recently been published, the recommendations of which are reviewed.

Characterization of a lipoprotein common to Legionella species as a urinary broad-spectrum antigen for diagnosis of Legionnaires' disease

We have previously identified the Legionella 19-kDa peptidoglycan-associated lipoprotein (PAL) as a species-common immunodominant antigen. We describe here for the first time the excretion and detection of the PAL antigen in infected urine specimens, which is useful for the diagnosis of Legionnaires' disease. Rabbit anti-PAL immunoglobulin G (IgG) antibody was produced by immunization with the purified, recombinant PAL of Legionella pneumophila serogroup 1 and used in the PAL antigen capture enzyme-linked immunosorbent assay (ELISA) to detect urinary PAL antigen. A soluble-antigen capture ELISA using rabbit IgG antibodies against Legionella soluble antigens was prepared independently and used as a broad-spectrum standard test to detect soluble antigens of several Legionella species. Urine samples were obtained from guinea pigs experimentally infected with each of L. pneumophila serogroups 1, 3, and 6, and other Legionella species. The absorbance values of the PAL antigen ELISA highly correlated with those of the soluble-antigen ELISA in infected urine samples, with a correlation coefficient of 0.84 (P < 0.01). When applied to 17 infected urine samples and 67 negative controls from guinea pigs, the sensitivity and specificity of the PAL antigen capture ELISA were 88.2 and 95.5%, respectively. Compared to the commercial Biotest enzyme immunoassay, the PAL antigen ELISA was more efficient for detecting pneumophila non-serogroup 1 and nonpneumophila species. None of the 161 control human urine specimens obtained from healthy adults and patients with either non-Legionella pneumonia or urinary tract infections tested positive in the PAL antigen ELISA. The present study shows that the Legionella PAL is a very useful broad-spectrum antigen for urinary diagnostic testing. Moreover, since recombinant PAL antigen can be produced more efficiently than the soluble antigens, the development of a broad-spectrum diagnostic immunoassay based on the detection of the PAL antigen appears to be warranted.

Detection of Legionella DNA by PCR of whole-blood samples in a mouse model

A detection system for Legionella DNA in blood samples based on the PCR was developed and evaluated in A/J mice with experimentally induced Legionella pneumonia. Primers were designed to amplify a 106 bp DNA fragment of the 16S rRNA gene specific to Legionella species. The PCR system could detect clinically relevant Legionella species including Legionella pneumophila, Legionella micdadei, Legionella bozemanae, Legionella dumoffii, Legionella longbeachae, Legionella gormanii and Legionella jordanis. The sensitivity of the PCR system was 20 fg extracted DNA. In the mouse model, the blood PCR was compared with results obtained by PCR on bronchoalveolar lavage fluid (BALF) samples, cultures of blood and BALF and detection of Legionella urinary antigen. Blood PCR was positive until 8 days after infection, while BALF PCR became negative on day 4. These results indicate that PCR using blood samples may be a useful, convenient and non-invasive method for the diagnosis of Legionella pneumonia.

Development of a multiplex real-time quantitative PCR assay to detect Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae in respiratory tract secretions

Atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae are an important cause of community-acquired pneumonia. The available detection methods (culture and serology) either lack sensitivity or give only a retrospective diagnosis. In order to improve their detection and quantification in respiratory samples, a real-time multiplex PCR, performed in two separate reactions, was developed for these three pathogens. The comparison of multiplex real-time and conventional PCR assay on 73 respiratory specimens showed an overall agreement of 98.3%, corresponding to 95.8%, 100% and 100% agreement for C. pneumoniae, L. pneumophila and M. pneumoniae, respectively. Clinical application of this multiplex real-time PCR was done on 40 respiratory samples from 38 patients with respiratory tract infections. Of 19 serology-positive patients, 14 were confirmed by the multiplex real-time PCR to be infected by either one of the three pathogens. All samples from serology-negative patients were negative with the multiplex real-time PCR.

Factors related to persistence of Legionella urinary antigen excretion in patients with legionnaires' disease

The aim of this prospective study was to compare patient characteristics, clinical data, and evolution of Legionella pneumophila pneumonia according to the duration of Legionella urinary antigen excretion. Urine samples from 61 patients with Legionella pneumonia diagnosed by detection of urinary antigen were obtained periodically until urinary antigen could no longer be detected. Cases were divided into two groups based on the duration of urinary antigen excretion: group I (46 patients, <60 days) and group II (15 patients, >or=60 days). Groups were compared for patient characteristics, clinical data, and evolution of pneumonia. Antigen excretion >or=60 days was observed significantly more frequently in immunosuppressed patients ( P=0.001) in whom the time to apyrexia was >72 h ( P=0.002), although only the time to apyrexia remained significant on multivariate analysis ( P=0.006). In conclusion, the duration of Legionella urinary antigen excretion was <60 days in most patients but was longer in immunosuppressed patients with a longer time to defervescence of fever.

Legionnaires disease with bacteremic coinfection

We describe 6 patients who had bacteremic community-acquired pneumonia and unsuspected Legionella pneumophila coinfection. We reviewed case records of patients who were diagnosed as having a recent Legionella infection on the basis of either the presence of L. pneumophila serogroup 1 antigen in urine or a 4-fold increase in L. pneumophila antibody level and with a blood culture that yielded a bacterium other than L. pneumophila. Three patients were diagnosed with legionellosis on the basis of the presence of antigen in urine, and 3 were diagnosed on the basis of a 4-fold increase in antibody titer. Of these 6 patients, 4 were infected with Streptococcus pneumoniae, 1 with Streptococcus pyogenes, and 1 with Enterobacter cloacae. L. pneumophila infection in these patients may have predisposed them to concomitant bacteremia. Initial empiric antimicrobial therapy for patients who live in areas of endemicity and who are smokers should be treated with antimicrobial agents that have activity against pneumococcus and Legionella species.

Population genetic structure of Legionella pneumophila inferred from RNA polymerase gene (rpoB) and DotA gene (dotA) sequences

The population structure of Legionella pneumophila was studied by using partial RNA polymerase gene (rpoB) and DotA gene (dotA) sequences. Trees inferred from rpoB sequences showed that two subspecies of L. pneumophila, Legionella pneumophila subsp. pneumophila and Legionella pneumophila subsp. fraseri, were clearly separated genetically. In both rpoB and dotA trees, 79 Korean isolates used in this study constituted six clonal populations, four of which (designated subgroups P-I to P-IV) were identified in L. pneumophila subsp. pneumophila and two of which (designated subgroups F-I and F-II) were identified in L. pneumophila subsp. fraseri. Although the relationships among subgroups were not identical, such subgrouping was congruent between the rpoB and dotA trees. Type strains of several serogroups did not belong to any subgroup, presumably because isolates similar to these strains were not present among our local sample of the population. There was evidence that horizontal gene transfer or recombination had occurred within L. pneumophila. Contrary to the phylogeny from rpoB and the taxonomic context, subgroups P-III and P-IV of L. pneumophila subsp. pneumophila proved to be closely related to those of L. pneumophila subsp. fraseri or showed a distinct clustering in the dotA tree. It can be inferred that dotA of subgroups P-III and P-IV has been transferred horizontally from other subspecies. The diverse distribution of serogroup 1 strains through the gene trees suggests that surface antigen-coding genes that determine serogroup can be exchanged. Thus, it can be inferred that genetic recombination has been important in the evolution of L. pneumophila.

The emerging role of atypical pathogens in community-acquired pneumonia

Community-acquired pneumonia (CAP) constitutes a major cause of morbidity and mortality. Although Streptococcus pneumoniae remains the bacterium most commonly implicated in CAP, the atypical respiratory pathogens Mycoplasma pneumoniae, Legionella species, and Chlamydia pneumoniae are being isolated with increasing frequency Contrary to previous beliefs, these agents are capable of causing severe as well as mild-to-moderate illness. Moreover, they can affect all age groups. Indeed, atypical pathogens are implicated in up to 40% of CAP cases and commonly occur as copathogens in mixed-infection CAP, an etiology associated with particularly high mortality (up to 25%). Laboratory methods for detecting atypical pathogens are slow, and there is significant overlap between atypical and typical CAP manifestations. For these reasons, accurate prediction of etiology cannot be made purely on clinical or radiologic grounds. Consequently, empiric antimicrobial therapy for atypical pathogens (with agents such as macrolides, fluoroquinolones, in some cases tetracyclines, or the new ketolides) warrants careful consideration and now is recommended for the treatment of CAP.

Assessment of a new test to detect Legionella urinary antigen for the diagnosis of Legionnaires' Disease

Given that the rate of mortality by Legionella pneumonia increases in incorrectly treated patients, rapid diagnosis and early antibiotic treatment are needed. We have assessed the performance of a new enzyme immunoassay (EIA) test (Bartels Inc. Trinity Biotech Company, Wicklow, Ireland) to detect Legionella pneumophila antigen in urine comparing it to Binax EIA (Binax, Portland, Maine). We also evaluated the capability of both EIAs to detect extracted soluble antigens of Legionella strains. Using nonconcentrated urine samples (NCU) the sensitivity of Bartels EIA was 74.1% (66/89) and the sensitivity of Binax EIA was 51.7% (46/89). The sensitivity of both EIA tests were 91.5% (54/59) using concentrated urine samples (CU). Specificity of both EIA tests was 100% in NCU and CU. Bartels EIA was able to detect all serogroup L. pneumophila antigens, achieving a higher sensitivity in the case of L. pneumophila serogroup 1 soluble antigen. The new EIA was found to be a useful test for the rapid diagnosis of Legionella pneumonia, being a better alternative to the Binax EIA if NCU is used.