Abstract

Background: Group B streptococcus (GBS) is the most common isolate in mother-related infection in newborns.

Aims: To evaluate the epidemiology of GBS infection in the first 90 days after birth; to determine if prophylaxis for early-onset neonatal GBS infection can be based only on risk factors.

Design: National epidemiological surveillance.

Methods: Between April 2001 and March 2005 active, systematic, voluntary, national surveillance was performed through the Portuguese paediatric surveillance unit. Case definition: any infant <90 days of age with GBS-positive culture in any normally sterile site—blood, cerebrospinal fluid (CSF), joint aspirate. Early-onset infection defined as in the first six full days after birth.

Results: 242 cases were reported (estimated cumulated incidence 0.54/1000 live births (95% CI 0.47 to 0.61)). Infection occurred before day 7 in 194 babies (81%); 13% presented between days 7 and 28; 6% between days 28–90. The incidence of early-onset infection was 0.44/1000 live births; 196 were term infants (81%), 160 of whom became ill before day 7; only 35 (22%) of these had one or more risk factors for infection. Overall, there were 229 positive blood cultures; 46 newborns had meningitis and 48 pneumonia. Mortality was 6.6% (16/242); it was similar for early (6.7%) and late-onset infection (6.3%), but varied by gestation—4.6% for term infants, 15.2% for preterm and 18% for babies born <1500 g.

Conclusion: GBS infection is predominantly an early infection of the term infant. Mortality is higher in preterm and very low birthweight infants. GBS prophylaxis based on risk factors would leave untreated 78% of term babies who will present with early-onset disease.