title: Interpretation of the presence of IgM and IgG antibodies in a rapid test for dengue: analysis of dengue antibody prevalence in Fortaleza City in the 20th year of the epidemic.
abstract: BACKGROUND
  The diagnosis of dengue and the differentiation between primary and secondary infections are important for monitoring the spread of the epidemic and identifying the risk of severe forms of the disease. The detection of immunoglobulin (Ig)M and IgG antibodies is the main technique for the laboratory diagnosis of dengue. The present study assessed the application of a rapid test for dengue concerning detection of new cases, reinfection recognition, and estimation of the epidemic attack rate.
  
  
  METHODS
  This was a retrospective, cross-sectional, descriptive study on dengue using the Fortaleza Health Municipal Department database. The results from 1,530 tested samples, from 2005-2006, were compared with data from epidemiological studies of dengue outbreaks in 1996, 2003, and 2010.
  
  
  RESULTS
  The rapid test confirmed 52% recent infections in the tested patients with clinical suspicion of dengue: 40% detected using IgM and 12% of new cases using IgG in the non-reactive IgM results. The positive IgM plus negative IgG (IgM+ plus IgG-) results showed that 38% of those patients had a recent primary dengue infection, while the positive IgG plus either positive or negative IgM (IgG+ plus IgM+/-) results indicated that 62% had dengue for at least a second time (recent secondary infections). This proportion of reinfections permitted us to estimate the attack rate as >62% of the population sample.
  
  
  CONCLUSIONS
  The rapid test for dengue has enhanced our ability to detect new infections and to characterize them into primary and secondary infections, permitting the estimation of the minimal attack rate for a population during an outbreak.
authors.affiliation: Célula de Vigilância Epidemiológica, Secretaria Municipal de Saúde de Fortaleza, Prefeitura Municipal de Fortaleza, Fortaleza, CE. rubens@saudefortaleza.ce.gov.br
authors.forename: José
authors.initials: J
authors.lastname: Rubens Costa Lima
authors.forename: Maria Zélia
authors.initials: MZ
authors.lastname: Rouquayrol
authors.forename: Maria Roseli
authors.initials: MR
authors.lastname: Monteiro Callado
authors.forename: Maria Izabel
authors.initials: MI
authors.lastname: Florindo Guedes
authors.forename: Claudia
authors.initials: C
authors.lastname: Pessoa
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000097:blood*; D001938:Brazil / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D003715:Dengue / Q000175:diagnosis / Q000453:epidemiology*; D003716:Dengue Virus / Q000276:immunology*; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007075:Immunoglobulin M / Q000097:blood*; D007223:Infant; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011933:Reagent Kits, Diagnostic; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D011933:Reagent Kits, Diagnostic