Tested once a fortnight
Uncertainty of Measurement: B. pertussis IgG: 6%
Whooping cough is caused by the bacterium Bordetella pertussis . It is an acute, highly contagious bacterial infection of the respiratory tract characterised by paroxysms of severe coughing. Serology has limited diagnostic utility (see below). This is particularly true for infants younger than 6 months who rarely develop antibodies. Acute infection should be diagnosed by submitting a nasopharyngeal swab for B. pertussis PCR.
Serology
Note: There is no serological test for immunity to B pertussis
Detection of antibody to pertussis is best performed by enzyme linked immunoassay (ELISA). The presence of specific IgA antibodies in a single sample combined with appropriate clinical symptoms is considered highly suggestive of an active infection. IgA antibodies specific to B.pertussis only occur during a natural infection and not following immunisation (with the exception of acellular vaccine booster which may stimulate IgA antibody). An in-house study of IgM responses in a predominantly adult population gave a high frequency of low positive results which were not useful in the diagnosis of current infection. An IgG ELISA can be helpful when both acute and convalescent serum specimens are available. A significant rise in IgG antibody is indicative of current or recent infection.
Blood samples obtained early during primary infection may not contain detectable antibodies. A second sample must be obtained 2-4 weeks later and tested in parallel with the original sample. A proportion of children and adolescents may not produce a detectable IgA during infection.
Studies of pertussis outbreaks suggest that vaccine induced immunity wanes within 5 to 10 years. Infection in vaccinated persons causes a milder, non-specific disease, characterized by a prolonged cough lasing several weeks to months.
Antibody Response.
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IgM and IgA antibodies appear during the first three weeks of infection and disappear in most cases with 6 months.
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IgA antibodies usually persist longer than IgM.
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IgA antibodies present only as a result of infection or in individuals given booster immunization with acellular vaccine.
References
Savyon Diagnostics SeroPertussis IgA/IgM kit insert.
For further information contact the laboratory (contact via Lablink: 22000 or (09) 307-8995 or 0800 522 7587) ,or:
the Virology team
virology@adhb.govt.nz