Respiratory viral testing for young febrile infants presenting to emergency care: a planned secondary analysis of the Febrile Infants Diagnostic assessment and Outcome (FIDO) prospective observational cohort study.

OBJECTIVE

To describe the association of respiratory viral test results and the risk of invasive bacterial infection (IBI) for febrile young infants presenting to emergency care.

DESIGN

A planned secondary analysis within the Febrile Infants Diagnostic assessment and Outcome (FIDO) study, a prospective multicentre observational cohort study conducted across the UK and Ireland.

SETTING

35 paediatric emergency departments and assessment units across the UK and Ireland between 6 July 2022 and 31 August 2023.

PATIENTS

Febrile infants aged 90 days and under presenting to emergency care.

MAIN OUTCOME MEASURES

IBI (meningitis or bacteraemia) among febrile infants, undergoing respiratory viral testing for respiratory syncytial virus (RSV), influenza and SARS-CoV-2.

RESULTS

1395 out of 1821 participants underwent respiratory viral testing, of those tested 339 (24.5%) tested positive for at least one of, SARS-CoV-2, RSV or influenza. A total of 45 infants (3.2%) were diagnosed with IBI. Of these, IBI occurred in 40 out of 1056 (3.8%) participants with a negative viral test and 5 out of 339 (1.5%) occurred in participants with a positive viral respiratory test (p=0.034). Infants aged 29 days and older with a positive respiratory viral test had a significantly lower rate of IBI (0.7%) compared with those with a negative test (3.2%) (p=0.015).

CONCLUSIONS

Young febrile infants with a positive respiratory viral test for SARS-CoV-2, RSV or influenza are at lower risk of IBI. Infants over 28 days of age with a positive viral test represent the lowest risk cohort.

TRIAL REGISTRATION NUMBER

NCT05259683.