Sensitivity and specificity of single IgA and IgG antibody concentrations for early diagnosis of pertussis in adults: an evaluation for outbreak management in public health practice.
BACKGROUND
An accurate, practical laboratory test is needed to confirm clinical diagnosis of pertussis in adults during the first 3 symptomatic weeks, when treatment is effective and transmission can be interrupted.


METHODS
The sensitivity and specificity of single IgA and IgG levels were assessed in a cohort study of a pertussis epidemic in 99 adults in a closed community. Sensitivities were assessed in the sera of 46 laboratory confirmed clinical pertussis cases during the first 3 weeks. Specificities were calculated in sera of 35 asymptomatic controls without clinical symptoms or laboratory confirmed infections from the same community (internal controls). We compared these specificities with the specificities of single IgA and IgG levels in 4275 external controls from a cross-section of the general Dutch population aged 21-79 years who had not coughed for more than 2 weeks in the past year, and without pertussis diagnoses. The study was done in the Netherlands when whole-cell pertussis vaccine was used in the national vaccination programme.


RESULTS
Levels of 24 U/ml for IgA and 27 U/ml for IgG gave sensitivities of 100% and 75%, respectively, in the first 2 weeks, 100% in the third week, and 97% after the fourth week. The levels were reached within 2 days after onset of increase, and remained above these levels for roughly 7.2 and 5.1 months, respectively. Specificity was 82% for IgA and 89% for IgG in the internal controls and 90% in the external controls, respectively.


CONCLUSIONS
We suggest levels of 24 U/ml for IgA level and 27 U/ml (= 27 International Units (IU)/ml) for IgG as sensitive, specific, and practical for laboratory confirmation of clinical pertussis in adults in the first 3 weeks of outbreak management.
Mertens
Paul L J M
PL
Department of Public Health, Erasmus MC, University Medical Center Rotterdam, CA Rotterdam, The Netherlands. paul.mertens@wxs.nl
Stals
Frans S
FS
Steyerberg
Ewout W
EW
Richardus
Jan H
JH
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001886:Bordetella pertussis / Q000276:immunology*; D016022:Case-Control Studies; D015331:Cohort Studies; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012680:Sensitivity and Specificity; D012698:Serologic Tests / Q000379:methods; D014917:Whooping Cough / Q000175:diagnosis / Q000276:immunology*
D007070:Immunoglobulin A; D007074:Immunoglobulin G