Vaccination status and severity of pertussis among hospitalized pediatric patients at a tertiary center in Riyadh: an exploratory study.

BACKGROUND: Pertussis remains a clinically significant vaccine-preventable respiratory infection, with the greatest morbidity concentrated in young infants who are not yet eligible for, or have not yet completed, the primary pertussis-containing vaccine series. Despite established immunization programs, hospitalizations continue to occur, and locally generated evidence is needed to describe clinical severity, complications, and healthcare utilization among admitted children.

OBJECTIVE: To describe the clinical characteristics, in-hospital management, and outcomes of children hospitalized with PCR-confirmed pertussis at King Saud Medical City (KSMC), Riyadh, and to explore unadjusted associations between pertussis vaccination status and severity-related outcomes.

METHODS: A retrospective exploratory chart review was conducted among children aged 0-14 years hospitalized with PCR-confirmed pertussis between 2023 and 2025. Disease severity was classified using an operational Pertussis Severity Score (PSS), with PSS > 5 indicating severe disease. Descriptive statistics summarized demographic characteristics, clinical presentation, laboratory findings, management, and outcomes. Unadjusted exploratory analyses were performed to assess associations between vaccination status and categorical severity-related outcomes using Pearson's chi-square test or Fisher's exact test, as appropriate. Effect estimates were reported with 95% confidence intervals where applicable.

RESULTS: The study included 50 children with a median age of 2.0 months (IQR 1.0-3.0); 50.0% were male. Common clinical features included cough (94.0%), paroxysms (88.0%), cyanosis (70.0%), recurrent apnoea (64.0%), vomiting (64.0%), hypoxemia (58.0%), and pneumonia (40.0%). Most patients had no documented pertussis-containing vaccine dose at admission (86.0%). Severe pertussis (PSS > 5) was identified in 52.0% of cases; 58.0% required oxygen therapy and 54.0% required ICU admission. In-hospital mortality occurred in 20.0% of admissions, reflecting the high-acuity tertiary referral setting. In unadjusted exploratory Fisher's exact analysis, severe pertussis occurred in 25 of 43 children with no documented pertussis-containing vaccine dose before admission compared with 1 of 7 children with at least one documented dose (58.1% vs. 14.3%; OR = 8.33, 95% CI: 0.92-75.36; p = 0.045). This association was borderline and imprecise, as reflected by the wide confidence interval.

CONCLUSION: Hospitalized pertussis at KSMC primarily affected very young infants and was characterized by substantial clinical severity, high ICU utilization, and notable in-hospital mortality within this tertiary referral setting. Children with no documented pertussis-containing vaccine dose were over-represented among severe cases; however, this unadjusted exploratory finding should be interpreted cautiously because age and vaccination eligibility were closely related in this very young admission sample. Larger prospective studies are needed to clarify vaccination-related predictors of pertussis severity while accounting for age eligibility and other potential confounders.