Value of negative nose and ear cultures in identifying high-risk infants without early-onset group B streptococcal sepsis.

Initiation of antibiotic therapy shortly after birth in infants at high risk for early-onset group B streptococcal sepsis is a common practice. The purpose of the current study was to evaluate whether the absence of group B streptococcal isolation from nose or ear cultures in such infants would have a high negative predictive value and low false-negative rate in predicting infants without sepsis and therefore whether such cultures would be of value in determining in which infants antibiotics could be safely discontinued. Infants admitted to the neonatal intensive care unit during 1989 and 1990 had a nasal culture obtained at admission and during 1991 and 1992 had an ear canal culture. Infants in whom sepsis was suspected had a blood culture in addition to a complete blood cell count, urine latex agglutination study for group B streptococci antigen, chest roentgenography and frequent monitoring of physiologic variables. The negative predictive value of nose and ear was 99% (2144 of 2149) and the false-negative rate was 7% (five negative surface cultures from 72 infants with sepsis in whom surface cultures were obtained). All five false-negative cultures were obtained from the ear canal. The false-negative rate of nose cultures was 0% (0 of 35). The high negative predictive value and low false-negative rate of nose cultures in identifying infants without sepsis suggest that nose cultures may provide additional valuable information in identifying the infant in whom antibiotics may be safely discontinued in the absence of other factors suggestive of systemic infection.