Five relevant clinical studies (1980-2004) found in a Medline, Pubmed and other database search were analyzed to determine the incidence of meningitis and the importance of routine lumbar puncture (LP) in late onset neonatal infection (greater than 48 hours), in a report from Northwick Park Hospital, Harrow, UK. CSF culture was positive in 1.3-3.5% of infants with suspected infection. Blood cultures were negative in 15-30% of infants with meningitis and positive CSF culture. Except for one study, LPs were not routine for investigation of infection, and were obtained in only 60% of those with positive blood culture. Almost one third of neonates with sepsis had coexisting meningitis.
Late onset meningitis is associated with predominantly Gram negative organisms. The incidence of viral and fungal (Candida albicans) organisms is higher in late onset compared to early onset infection. Group B streptococcal infection presenting late is more likely to be associated with meningitis.
Low rates of LP were attributed to perceived adverse effects of the procedure, the babies being considered “too sick to tap.” In the studies reviewed, LP was not associated with complications (risk of trauma, infection, spinal epidermoid tumor, brain stem herniation, or hypoxic stress). The risk of death was 23% in infants with meningitis versus 9% in those with LP and no meningitis. The rate of positive CSF cultures among patients with LP was not significantly different across centers. The importance of a repeat LP to determine effectiveness of treatment is emphasized by the finding of 10 of 90 repeat cultures being positive for the same organism. 
COMMENT. The authors conclude that lumbar puncture should be considered as part of the routine investigation of late onset infection (after 48 hours) in neonates. LP performed in 30 to 90 infants (depending on the patient population) during investigation for serious bacterial illness would detect one case of meningitis.