OBJECTIVE To analyze the clinical characteristics and pathogens for mixed infections in children with pertussis, so as to references for clinical diagnosis and treatment.

METHODS A retrospective analysis was conducted on the clinical data of 350 children diagnosed with pertussis and hospitalized in Wuhan Children′s Hospital from Jan. 2022 to Dec. 2023. The clinical characteristics, peak white blood cell count, peak lymphocyte ratio, high-sensitivity C-reactive protein or C-reactive protein, procalcitonin and complications were compared between different age groups, as well as between the single infection group and the mixed infection group.

RESULTS Mixed infections were observed in 291 children (83.14%), predominantly viral (63.43%, 222/350), with human rhinovirus/enterovirus being the most common (32.57%, 114/350). For children aged < 6 months, 6 months to < 1 year and 1 to < 3 years, the incidence of family contact history of cough, panting, hasty breathing, respiratory failure, peak white blood cell count and peak lymphocyte ratio were all higher than those aged 3 to < 6 years and ≥6 years (all P < 0.05). The incidence of post-cough vomiting was higher in children aged 6 months to < 1 year and 1 to < 3 years compared to other age groups (P < 0.05). The length of hospital stay decreased with increasing age (P < 0.05). The proportions of children with paroxysmal spasmodic cough, post-cough cyanosis, post-cough flushing, coughing spells, inspiratory three concave sign, pneumonia and pulmonary phlegm rales all generally decreased with age (all P < 0.05). Nodding respiration was only observed in children aged < 1 year (P < 0.05). The incidence of fever, co-infection with bacteria and Mycoplasma pneumoniae infection was higher in children aged 6 months to < 1 year, 1 to < 3 years, 3 to < 6 years and ≥6 years compared to those aged < 6 months (all P < 0.05). The incidence of fever was higher in the mixed infection group than that in the single infection group (P < 0.05). Children in the single infection group had longer hospital stays, higher incidence of paroxysmal spasmodic cough, nocturnal cough, post-cough flushing, coughing spells, pulmonary phlegm rales and higher peak lymphocyte ratio (all P < 0.05). The incidence of paroxysmal spasmodic cough was higher in the single infection group for children aged < 3 months (P < 0.05).

CONCLUSIONS The younger children with pertussis have a higher proportion of family contact history of cough and are more prone to clinical manifestations such as paroxysmal spasmodic cough, post-cough vomiting, post-cough cyanosis, and pneumonia. They also have higher peak white blood cell counts, peak lymphocyte ratios and longer hospital stays. As children′ age increased, the incidence of fever, bacterial, and mycoplasma infections also increased. The types of pathogens in mixed infections varies with patients′ age and pertussis mixed infections may mask typical clinical symptoms.