What is the recommended next step in managing an infant presenting with symptoms of bacterial meningitis?

In the management of an infant presenting with symptoms of bacterial meningitis, the immediate priority is to establish a diagnosis and start appropriate treatment as soon as possible. An urgent lumbar puncture is crucial for obtaining cerebrospinal fluid (CSF) for analysis, which can confirm the presence of infection and identify the causative organism. This procedure allows for the examination of the CSF for features typical of bacterial meningitis, such as elevated white blood cell counts, increased protein levels, and decreased glucose levels.

Simultaneously, it is essential to initiate empirical intravenous antibiotics without delay, as bacterial meningitis can progress rapidly and become life-threatening. Early administration of antibiotics significantly improves outcomes and can prevent complications associated with the infection.

Other options, such as an MRI scan, are not appropriate in this acute setting since they can delay treatment. While imaging may be indicated later to assess for complications or other conditions, the immediate focus must be on confirming the diagnosis and starting antibiotics. Similarly, ordering a full blood count or merely monitoring vital signs does not address the urgent need for treatment and could lead to deterioration in the patient's condition. Therefore, performing an urgent lumbar puncture followed by the initiation of antibiotics is the best course of action.