Serum Immunoglobulin G Analysis to Establish a Delayed Diagnosis of Chronic Cough due to Bordetella pertussis

Objectives Incidence of Bordetella pertussis infection among adults has risen significantly throughout the United States, but pertussis is not often considered in the differential diagnosis of chronic cough in adults. The authors hypothesized that serum IgG testing can establish a diagnosis of pertussis infection late in disease presentation when cultures and polymerase chain reaction (PCR) testing are not reliable. Study Design Case series with chart review. Setting Tertiary care hospital. Subjects and Methods Institutional B pertussis serum IgG and PCR tests were reviewed since 2007. Clinical factors assessed included vaccination history, duration and severity of cough, and general medical history. Results Forty‐eight patients had B pertussis fimbrial agglutinogen IgG levels tested since 2007, with a significant increase in positive IgG tests (>27 IU/mL, 3 times the upper limit of normal) since fall 2009. Nineteen patients (39.5%) met IgG criteria for likely recent pertussis infection. Six IgG‐positive patients also had PCR swab testing performed, with 50% positive for B pertussis . IgG values were similar for patients with positive or negative B pertussis PCR testing with positive IgG titers. IgG‐positive patients were much more likely to have posttussive syncope. Recent vaccination for pertussis within the 3 years prior to IgG testing did not significantly increase IgG levels. Conclusions One‐time B pertussis serum IgG testing and patient history can establish a likely diagnosis of recent pertussis infection in the adult patient with chronic cough late in disease presentation when PCR testing is often negative. Pertussis should be considered in the differential diagnosis of all patients with chronic cough.