Abstract Title: Association of invasive bacterial infections and under-vaccinated status in well-appearing pediatric patients presenting to the emergency department with fever.

Background: Fever accounts for up to 40% of visits to the pediatric emergency department (ED). While fever can be caused by viral or bacterial infections, those developing invasive bacterial infections (IBI) are at increased risk for life-threatening complications. Thus, evaluating a patient’s risk factors—including assessment of vaccination status—for developing IBI is an essential step. For example, invasive illness from Haemophilus influenzae (Hib) was the leading cause of childhood bacterial meningitis prior to the advent of the vaccine, with around 200,000 cases occurring yearly. Over the decade following the vaccine introduction, the prevalence of invasive disease from bacteria, such as Hib, had been almost eradicated. This study aims to determine the association between vaccination status and IBI in well-appearing pediatric patients presenting to the ED with a chief complaint of fever.

Methods: This is a retrospective cohort study conducted between 2019-2023, at a single, urban tertiary care pediatric emergency department. Patients were included if their age was between 61 days and 18 years old presenting with a chief complaint of fever. Patients were excluded if they received antibiotics within 3 days or underwent surgery within 2 weeks of presentation. IBI was defined as bacteremia, bacterial meningitis, septic arthritis, osteomyelitis, pneumonia, deep neck space infection, mastoiditis, or orbital cellulitis. Prevalence of IBI was described and compared by presence of age group, chronic medical condition, gender, and vaccination status. Logistic regression was used to analyze the association between IBIs and vaccination status.

Results: 2,623 patients were screened, and 1249 patients were included. Amongst patients who were included, the prevalence of IBI in the study was 11.9%. Of the 80 under-immunized patients, nine (11.25%) developed an IBI. One hundred and forty (12%) of the 1,169 fully immunized patients developed an IBI. The odds ratio is 1.07 (95%CI 0.52-2.20).

Conclusion: In conclusion, the preliminary data does not show a significant difference in risk of IBI in patients who are under-immunized versus those who are fully immunized. Thus, clinicians should exercise caution using vaccination status alone to determine risk of IBI in well-appearing febrile pediatric patients presenting to the emergency department. However, low rates of IBI and under-vaccinated status as well as herd immunity in our population may indicate sample bias. Our future research aims to increase the sample size to further investigate this concept.