title: [Evaluation of an IgG avidity commercial test: contribution to diagnosis of primary infection caused by Toxoplasma gondii].
abstract: BACKGROUND
  Toxoplasmosis (T) is a major chronic parasitic infection in immunocompromised patients and pregnant women. It is important to discriminate between acute phase (AT) and chronic phase (CT). Diagnosis is serological in immunocompetent patients (concentration of IgG and IgM).
  
  
  OBJECTIVE
  To evaluate the utility of an IgG avidity test (A-IgG) to identify the acute and chronic stage. Avidity is the strength of affinity between a specific immunoglobulin and the protein antigenic epitope of the infecting agent, an affinity that increases over time.
  
  
  METHODS
  We used a qualitative kit that measures the avidity of IgG, discriminating the two phases. In 35 patients with clinical diagnosis of AT and/or CT, IgG, IgM and IgG A (VIDAS®) were performed.
  
  
  RESULTS
  Patients with AT were positive for IgM and IgG, but presented weak avidity. In the 21 cases with CT, 52% (n: 11) were IgM positive and 100% (n: 21) had positive IgG with strong avidity.
  
  
  CONCLUSIONS
  The results confirm that the test of A-IgG may be useful in the diagnosis of AT, and has 100% concordance with reference test (qualitative IgM + quantitative IgG). The result is available within 24 hrs, and may be useful in diagnosis of AT in pregnant women.
authors.affiliation: Laboratorio de Microbiología, Servicio de Laboratorios Clínicos, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: Marilena
authors.initials: M
authors.lastname: Canales R
authors.forename: Felipe
authors.initials: F
authors.lastname: Navia G
authors.forename: Marisa
authors.initials: M
authors.lastname: Torres H
authors.forename: Mónica
authors.initials: M
authors.lastname: Concha C
authors.forename: Ana M
authors.initials: AM
authors.lastname: Guzmán D
authors.forename: Carlos
authors.initials: C
authors.lastname: Pérez C
authors.forename: Patricia
authors.initials: P
authors.lastname: García C
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000913:Antibodies, Protozoan / Q000097:blood / Q000276:immunology*; D000915:Antibody Affinity / Q000276:immunology*; D002648:Child; D002908:Chronic Disease; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology*; D007075:Immunoglobulin M / Q000097:blood / Q000276:immunology*; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000175:diagnosis / Q000276:immunology; D011933:Reagent Kits, Diagnostic; D014122:Toxoplasma / Q000276:immunology*; D014123:Toxoplasmosis / Q000175:diagnosis* / Q000276:immunology; D055815:Young Adult
chemical_list: D000913:Antibodies, Protozoan; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D011933:Reagent Kits, Diagnostic