Adult pertussis in the acellular-cell vaccine era: Comparative analysis of pertussis toxin antibodies in hospitalized patients with prolonged cough

In the past two years, pertussis cases in China have reemerged, shifting from infants to older children (≥6 years). In adults, underdiagnosis is common due to symptom overlap with other cough disease and limited testing, highlighting the need for better assessment in prolonged cough cases. Residual serum samples from 589 adults hospitalized with prolonged cough (≥2 weeks) formed the case group, while 589 age-, sex-, and region-matched non-cough patients served as controls. PT-IgG levels, measured via ELISA, indicated past (≥62.5 IU/mL) or recent infection (≥100 IU/mL, within a year). PT-IgG ≥ 62.5 IU/mL was detected in 17.0% of cases vs. 2.7% of controls, and ≥100 IU/mL in 7.3% vs. 1.0%. Cases had a higher median PT-IgG (16.74 vs. 2.50 IU/mL, <i>p</i> < .001). Among cases, those aged 60-69 had the highest PT-IgG ≥62.5 IU/mL (20.6%, <i>P</i> > .05). No significant difference in PT-IgG ≥ 62.5 IU/mL was observed between males and females in either group. No patients had documented pertussis. Pneumonia and chronic obstructive pulmonary disease (COPD) were the most common comorbidities in PT-IgG ≥ 62.5 IU/mL cases (43.0% vs. 40.0%), similar to PT-IgG < 62.5 IU/mL cases (37.6% vs. 43.6%). A significant proportion of hospitalized adults with a cough ≥2 weeks have serological evidence of pertussis, which could be often misdiagnosed as pneumonia or COPD. It should be considered in differential diagnoses and confirmed with laboratory testing.