Evaluation of serotyping methodology of invasive and nasopharyngeal isolates of Haemophilus influenzae in the ongoing surveillance in Brazil
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2003-12
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To assess the magnitude of discrepant results obtained by routine Haemophilus influenzae serotyping, 258
isolates, collected by the epidemiological surveillance system in Brazil from individuals with invasive diseases
or carriage, were evaluated by two slide agglutination (SlAg) methods: SlAg method 1, by which strains were
initially screened with a serotype b-specific antiserum, and SlAg method 2, by which strains were tested against
all serotype-specific antisera in parallel. Investigators comparing results of the two SlAg methods with those
obtained by capsule type-specific PCR were blinded to the method used. The serotype prevalence rates found
by the three methods were significantly different, involving discrepancies mainly between serotype b and
noncapsulated (NC) isolates. For invasive isolates (n 131), the overall agreement rate between SlAg method
1 or 2 and PCR was 68.0 or 88.3%, respectively, whereas for colonizing isolates (n 127) the corresponding
rate was 46.5 or 94.2%, respectively. SlAg method 2 improved the ascertainment of serotypes over that obtained
with SlAg method 1, demonstrating good correlation with PCR. Use of the polyvalent antiserum as a screening
reagent for SlAg for invasive and colonizing isolates showed poor discriminatory power, with a sensitivity of
65.8% and a specificity of 91.7%. We stress the importance of using a well-standardized SlAg methodology and
suggest that reference laboratories should utilize PCR routinely to confirm SlAg results and to check all
nonspecific SlAg reactions and apparent NC isolates by SlAg in order to provide reliable data on the prevalence
of H. influenzae serotypes in the H. influenzae type b vaccine era.
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BOKERMANN, Sérgio et. al. Evaluation of serotyping methodology of invasive and nasopharyngeal isolates of Haemophilus influenzae in the ongoing surveillance in Brazil. Journal of Clinical Microbiology, Washington, v. 41, n. 12, p. 5546-5550, 2003.