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Microbiological and serological diagnosis of pertussis
1Swedish Institute for Infectious Disease Control, Solna. Hans.Hallander@smi.ki.se
Abstract:
Swedish vaccine trials have been used to examine sensitivity and specificity of diagnostic procedures for Bordetella pertussis infection. The proportions of cases diagnosed by culture and serology were 55% and 45%, respectively, when both methods were optimized. The culture method included nasopharyngeal aspiration, direct inoculation on plates, enrichment, and repeated collection of samples. An enzyme-linked immunosorbent assay for IgG antibodies to pertussis toxin (PT) and to filamentous hemagglutinin, with paired sera, was used for serology. Preexposure sera other than the acute serum increased the sensitivity of serology by 10%. A serology quality-assurance program to control imprecision and allow comparability over time and between laboratories is described. The direct fluorescent antibody technique had a sensitivity of 38% and a specificity of 99.6% in comparison with culture. A nested polymerase chain reaction (PCR) with the PT promoter region as target was 95% sensitive in comparison with culture if a cation-exchange resin was used to reduce inhibition. PCR enabled us to identify 83 positive samples in addition to 215 culture-positive ones-an increase of 38%--all with other indicators of pertussis infection.
Insights
Optimizing diagnostic methods for Bordetella pertussis infection is crucial. Nested PCR demonstrated high sensitivity (95%) compared to culture, significantly increasing positive case identification for pertussis.
Area of Science:
- Medical Microbiology
- Vaccinology
- Diagnostic Immunology
Background:
- Accurate diagnosis of Bordetella pertussis infection is essential for effective treatment and control.
- Traditional diagnostic methods like culture and serology have limitations in sensitivity and specificity.
- Evaluating novel diagnostic techniques is critical for improving pertussis case detection.
Purpose of the Study:
- To evaluate the sensitivity and specificity of various diagnostic procedures for Bordetella pertussis.
- To compare the performance of culture, serology, direct fluorescent antibody technique, and nested PCR.
- To assess the impact of pre-exposure sera on serological diagnostic accuracy.
Main Methods:
- Optimized culture methods including nasopharyngeal aspiration and enrichment.
- Enzyme-linked immunosorbent assay (ELISA) for IgG antibodies to pertussis toxin (PT) and filamentous hemagglutinin using paired sera.
- Direct fluorescent antibody (DFA) technique.
- Nested polymerase chain reaction (PCR) targeting the PT promoter region, with cation-exchange resin to mitigate inhibition.
Main Results:
- Optimized culture and serology diagnosed 55% and 45% of cases, respectively.
- Pre-exposure sera improved serology sensitivity by 10%.
- DFA sensitivity was 38% with 99.6% specificity versus culture.
- Nested PCR achieved 95% sensitivity compared to culture, identifying an additional 38% of positive cases.
Conclusions:
- Nested PCR offers a highly sensitive diagnostic method for Bordetella pertussis, significantly enhancing detection rates.
- Optimized serological testing, particularly with pre-exposure sera, improves diagnostic yield.
- A quality-assurance program is vital for reliable and comparable serological results across laboratories and time.
- Combined diagnostic approaches may be necessary for comprehensive pertussis diagnosis.