Bacterial Meningitis in 5 week old baby boy

Mother tested negative to GBS. Gave birth to a baby boy vaginally. Baby was diagnosed with bacterial meningitis at 5 weeks. Was told by doctors that it was because mother was probably GBS positive. Baby and mother finally home. Wondering if the tests were done correctly or if some steps were not taken during labor that could have prevented this. Baby has hearing loss in right ear, needs to be taken to early intervention programs. Was admitted to hospital on 12/13/14 and discharged on 1/4/15.