Abstract
New diagnostic tests for the etiology of childhood pneumonia are needed. We evaluated the antibody-in-lymphocyte supernatant (ALS) assay to detect immunoglobulin (Ig) G secretion from ex vivo peripheral blood mononuclear cell (PBMC) culture, as a potential diagnostic test for pneumococcal pneumonia. We enrolled 348 children with pneumonia admitted to Patan Hospital, Kathmandu, Nepal between December 2015 and September 2016. PBMCs sampled from participants were incubated for 48 h before harvesting of cell culture supernatant (ALS). We used a fluorescence-based multiplexed immunoassay to measure the concentration of IgG in ALS against five conserved pneumococcal protein antigens. Of children with pneumonia, 68 had a confirmed etiological diagnosis: 12 children had pneumococcal pneumonia (defined as blood or pleural fluid culture-confirmed; or plasma CRP concentration ≥60 mg/l and nasopharyngeal carriage of serotype 1 pneumococci), and 56 children had non-pneumococcal pneumonia. Children with non-pneumococcal pneumonia had either a bacterial pathogen isolated from blood (six children); or C-reactive protein <60 mg/l, absence of radiographic consolidation and detection of a pathogenic virus by multiplex PCR (respiratory syncytial virus, influenza viruses, or parainfluenza viruses; 23 children). Concentrations of ALS IgG to all five pneumococcal proteins were significantly higher in children with pneumococcal pneumonia than in children with non-pneumococcal pneumonia. The concentration of IgG in ALS to the best-performing antigen discriminated between children with pneumococcal and non-pneumococcal pneumonia with a sensitivity of 1.0 (95% CI 0.73–1.0), specificity of 0.66 (95% CI 0.52–0.78) and area under the receiver-operating characteristic curve (AUROCC) 0.85 (95% CI 0.75–0.94). Children with pneumococcal pneumonia were older than children with non-pneumococcal pneumonia (median 5.6 and 2.0 years, respectively, p < 0.001). When the analysis was limited to children ≥2 years of age, assay of IgG ALS to pneumococcal proteins was unable to discriminate between children with pneumococcal pneumonia and non-pneumococcal pneumonia (AUROCC 0.67, 95% CI 0.47–0.88). This method detected spontaneous secretion of IgG to pneumococcal protein antigens from cultured PBMCs. However, when stratified by age group, assay of IgG in ALS to pneumococcal proteins showed limited utility as a test to discriminate between pneumococcal and non-pneumococcal pneumonia in children.
Highlights
Pneumonia is the leading cause of childhood mortality after the neonatal period, yet the pathogen-specific etiology of childhood pneumonia remains poorly defined (Liu et al, 2016; Feikin et al, 2017b)
356 (19%) children had a clinician diagnosis of pneumonia, as had an additional 37 children who were diagnosed with pneumonia, but not admitted, totaling 393 children. 369 children were enrolled to the study, with data on ALS to pneumococcal proteins available on 348 of these children (Figure 2)
The development of novel diagnostic tests for the etiology of pneumonia is partly driven by the need to assess the impact of vaccination strategies on the total, and pathogen-specific burden of pneumonia in diverse settings
Summary
Pneumonia is the leading cause of childhood mortality after the neonatal period, yet the pathogen-specific etiology of childhood pneumonia remains poorly defined (Liu et al, 2016; Feikin et al, 2017b). Using data from randomized controlled vaccine trials, vaccine-probe studies help reveal the pathogen-specific burden of disease by estimating the difference in disease between vaccinated and unvaccinated individuals (Feikin et al, 2014). Results from these studies estimate that approximately one third of children with pneumonia and radiographic consolidation have pneumococcal pneumonia in settings prior to the introduction of vaccines that prevent etiology-specific pneumonia, regardless of geography (O’Brien et al, 2009; Wahl et al, 2018). Culture of bacteria from blood is the most widely used test for bacterial pneumonia in children admitted to hospital. In the recent Pneumonia Etiology Research for Child Health (PERCH) casecontrol study, quantitative (q)PCR of lytA to determine whole blood pneumococcal load (Deloria Knoll et al, 2017), and density of nasopharyngeal (NP) colonization with S. pneumonia (Baggett et al, 2017), demonstrated only moderate ability to discriminate between pneumococcal pneumonia and agematched community children
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