title: The serological diagnosis of staphylococcal infective endocarditis.
abstract: OBJECTIVE
  Establishing the diagnosis of infective endocarditis (IE) can be difficult when blood cultures remain sterile or echocardiography is inconclusive. Staphylococcus aureus is a common aetiological microorganism in IE and is associated with severe valvular destruction and increased mortality. Early diagnosis using culture and antibiotic independent tests would be preferable to allow prompt antibiotic administration. We have developed and evaluated 2 serological assays for the rapid identification of a staphylococcal aetiology in infective endocarditis. The assays measure IgG against whole cells of S. aureus and IgG against lipid S, a novel extracellular antigen released by Gram-positive microorganisms.
  
  
  METHODS
  Serum was collected from 130 patients with IE and 94 control patients. IgG against whole cells of S. aureus and against lipid S was measured by enzyme linked immunosorbent assay (ELISA).
  
  
  RESULTS
  Anti-lipid S IgG titres were higher in IE caused by Gram-positive microorganisms than in controls (p<0.0001) and higher in staphylococcal IE than in both controls and IE caused by other microorganisms (p=0.0003). Anti-whole cell staphylococcal IgG was significantly higher in serum from patients with staphylococcal IE than in IE caused by other microorganisms and control samples (p<0.0001).
  
  
  CONCLUSIONS
  High anti-whole cell IgG titres are predictive of a staphylococcal aetiology in IE. Elevated serum anti-lipid S IgG titres are predictive of Gram-positive infection compared to controls, very high titres being associated with staphylococcal IE.
authors.affiliation: Department of Cardiology, Queen Elizabeth Hospital, Edgbaston, Birmingham B15 2TH, UK.
authors.forename: R W
authors.initials: RW
authors.lastname: Watkin
authors.forename: S
authors.initials: S
authors.lastname: Lang
authors.forename: P A
authors.initials: PA
authors.lastname: Lambert
authors.forename: W A
authors.initials: WA
authors.lastname: Littler
authors.forename: T S J
authors.initials: TS
authors.lastname: Elliott
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood*; D004697:Endocarditis, Bacterial / Q000097:blood / Q000175:diagnosis*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D012698:Serologic Tests; D013203:Staphylococcal Infections / Q000097:blood / Q000175:diagnosis*; D013211:Staphylococcus aureus / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D007074:Immunoglobulin G