Pneumococcal pneumonia diagnosis by demonstration of pneumolysin antibodies in precipitated immune complexes: a study in 350 Philippine children with acute lower respiratory infection

Vaccine preventable community-acquired pneumonia in hospitalized children in Northwest China

BACKGROUND

Community-acquired pneumonia (CAP) is a major cause of morbidity in industrialized countries and morbidity/mortality in developing countries. In China, comprehensive studies of the etiology of CAP in children aged between 2 months and 14 years who are serious enough to require hospitalization are lacking. Previous studies have been limited in child age range, focused on fatal cases, and/or limited in etiologies sought. An understanding of the etiologies is needed for development of best prevention and management practices.

OBJECTIVE

The aim of this study was to prospectively determine during a 12-month period the etiology of CAP in hospitalized children in a center in Northwest China.

DESIGN/METHODS

A prospective 12-month study (2004-2005) of CAP cases in children who were 2 months to 14 years of age admitted to the Second Hospital of Lanzhou University, China. Testing included admission and 1-month postdischarge serum for viral and bacterial serologic analyses (respiratory syncytial virus, influenza A and B, paraflu 1-3, adenovirus; Streptococcus pneumoniae, Haemophilus influenza B, Mycoplasma, and Moraxella. catarrhalis), blood culture, a nasopharyngeal aspirate for viral antigen testing, and a chest radiograph on admission and 1 month postdischarge. The study was funded by Lanzhou University. The study was performed in compliance with the guidelines of the institutional review board of the Second Hospital of Lanzhou University.

RESULTS

CAP was the admitting diagnosis for 29% of all admissions during the 12-month study. Of the 884 CAP cases, 821 (93%) were enrolled and completed the study. The age range was 2 months to 14 years; mean age was 2.3 years; 40% were <1 year. The average length of stay was 9.2 days (range, 6-20) but varied by age and etiology. Fourteen percent had received antibiotics before admission and 14% had underlying illnesses; 12% required intensive care unit treatment and 5 died. A microbial etiology for CAP was identified in 547 (67%); viral 535 (43%), bacterial 228 (27%), mixed viral bacterial 107 (13%), mixed viral in 1%, and mixed bacterial in 1%. The etiology varied by age; respiratory syncytial virus was most common in <1 year, S. pneumoniae and Hib 1-3 years, and Mycoplasma 5 years. Three potentially vaccine preventable etiologies accounted for 35% of the cases: influenza 9%, Hib 12%, and S. pneumonia 14%.

CONCLUSIONS

CAP is a major cause of childhood admission in China. Given the etiologic findings in this study, potentially 25% to 35% of cases could be prevented if seasonal influenza vaccine and conjugated H. influenza b and conjugated pneumococcal vaccines were introduced into routine practice.

Novel approaches to the identification of Streptococcus pneumoniae as the cause of community-acquired pneumonia

Current diagnostic tests lack sensitivity for the identification of the bacterial etiology of pneumonia. Attempts during the past 2 decades to improve sensitivity of detection of bacterial constituents in blood by use of antibody-antigen complexes and polymerase chain reaction have been disappointing. Recent data using pneumococcal conjugate vaccines as probes suggest that increased levels of both C-reactive protein and procalcitonin may be useful adjuncts to chest radiographs in the selection of patients with presumed bacterial pneumonia for inclusion in clinical trials. Among pneumococcal diagnostics currently under investigation, quantitative real-time polymerase chain reaction of respiratory secretions, as well as urinary antigen detection and pneumococcal surface adhesin A serological analysis for adults, are candidates for use in future clinical trials of antibiotics.

The genes encoding virulence-associated proteins and the capsule of Streptococcus pneumoniae are upregulated and differentially expressed in vivo

The polysaccharide capsule of Streptococcus pneumoniae and several well-characterized virulence proteins are known to contribute to the pathogenesis of pneumococcal disease. However, there is a paucity of data on the expression of their respective genes in vivo. In this study, the relative abundance of the mRNA transcripts of the genes encoding pneumolysin (ply), pneumococcal surface protein A (pspA), pneumococcal surface antigen A (psaA) and choline-binding protein A (cbpA), and of the first gene of the capsular polysaccharide biosynthesis locus (cps2A), was measured in virulent type 2 pneumococci harvested from the blood of BALB/c mice at 12 h and 24 h following intraperitoneal infection. The mRNA levels were then compared, using relative quantitative RT-PCR, with those present in organisms grown in serum broth. The expression of ply was upregulated threefold at 12 h, and 10-fold at 24 h post-infection; the expression of pspA and psaA was upregulated threefold and fivefold, respectively, at 12 h post-infection. Interestingly, the expression of pspA was 36-fold higher at 24 h post-infection whereas the expression of cps2A was upregulated approximately fourfold at 12 and 24 h post-infection. However, cbpA mRNA levels remained comparable in vivo and in vitro. When organisms were grown in whole blood or THY broth, the relative expression of these genes in the two growth media also differed markedly. This work provides direct molecular evidence that known virulence-associated genes of S. pneumoniae are differentially expressed in vivo. Data on the relative expression of these genes in different growth media also suggests that the regulation of expression of these genes is highly complex and multifactorial.

Gram-Positive Pneumonia

Gram-positive pneumonia is a leading cause of morbidity and mortality throughout the world. Of the gram-positive pathogens that cause pneumonia, Streptococcus pneumoniae and Staphylococcus aureus are the most common. The diagnosis of gram-positive pneumonia remains less than satisfactory, and newer diagnostic techniques such as antibody- and polymerase chain reaction-based antigen detection have yet to prove themselves. Drug resistance among gram-positive organisms is now endemic throughout the world and remains a serious therapeutic problem despite the availability of new antimicrobials. Efforts to control the spread of resistant strains include, in the case of S. aureus, stringent isolation policies and topical treatment to reduce carriage and, for S. pneumoniae, increased use of available vaccines and the develop- ment of more immunogenic vaccines.