Social patterns of inequity in the 2023–2024 pertussis outbreak in Barcelona: a cross-sectional population-based study

Pertussis (whooping cough) incidence follows a cyclical and bimodal pattern, predominantly affecting children and adolescents. The aim of this study was to describe social inequalities in pertussis incidence in the city of Barcelona during 2023–2024 outbreak. A population-based cross-sectional study of confirmed pertussis cases was conducted. Frequencies were calculated. Adjusted cumulative incidence ratios (aCIR) and their 95% confidence intervals (95% CI) were estimated using robust Poisson regression models with robust variance were fitted, adjusting for individual-level variables (age and income level of country of birth) and ecological variables (Socioeconomic Composite Index [SCI] and vaccination coverage of the primary healthcare area [PHA]). A total of 1,890 cases were confirmed, of which 55.7% occurred in women. Incidence was concentrated in children and adolescents, while women showed significantly higher incidence ratio across all age groups. Multivariable models showed a significantly higher pertussis incidence among individuals born in high-income countries (aCIR men =4.43; 95% CI [3.25;6.04]; aCIR women =3.43; 95% CI [2.43;4.85]) and low-income countries (aCIR men =1.79; 95% CI [1.39;2.30]; aCIR women =1.70; 95% CI [1.33;2.16]), compared with individuals born in Spain. A gradient in pertussis incidence was observed with SCI, with incidence progressively increasing from high- to medium- (aCIR men =1.13; 95% CI [1.01;1.28]; aCIR women =1.23; 95% CI [1.08;1.39]) and low-income PHA (aCIR men =1.42; 95% CI [1.17;1.72]; aCIR women =1.44; 95% CI [1.22;1.70]). Among women, the quintile with the lowest vaccination coverage was associated with lower pertussis incidence (aCIR = 0.78; 95% CI [0.64;0.94]). In a context of high vaccination coverage, social inequalities were identified during the 2023–2024 pertussis outbreak in the city of Barcelona. Living in areas with the lowest socioeconomic index and having a migratory background were the factors most strongly associated with a higher pertussis incidence rate.