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Two term neonates born within four days of each other at a small hospital developed sepsis and meningitis caused by a unique strain of Citrobacter diversus not previously reported to cause meningitis. Eleven (27.5%) of 40 other infants admitted to the nursery during the epidemic period developed rectal or umbilical colonization by C. diversus. Contact soon after birth with either of two nurses was more common among infected or colonized infants than among infants who were not infected or colonized. Hand cultures of both nurses and a rectal culture of one of the nurses yielded the epidemic strain. C. diversus may have been introduced into the nursery by the rectal carrier and spread person to person. Six weeks later continued surveillance identified a second cluster (of four colonized infants) associated with a mother who was a carrier of C. diversus and whose newborn infant became colonized at birth. The outbreak ended after strict control measures were used.

Brain abscess is an infrequent complication of meningitis, including cases caused by Gram-negative enteric bacteria in neonates. Because brain abscesses recently developed in four of five neonates with Citrobacter diversus meningitis at one institution, we reviewed cases of C diversus meningitis reported in the literature and those enrolled in the Neonatal Meningitis Cooperative Study Groups and reported to the Centers for Disease Control. Seventy-four cases in neonates were identified, and a brain abscess had developed in 41 (77%) of 53 patients for whom the information was available. This high frequency indicates the need for rapid diagnosis of this complication of C diversus meningitis.

During an outbreak of neonatal meningitis caused by kanamycin-resistant Citrobacter diversus, a field procedure for presumptive identification of the organism was evaluated, and using it resulted in the early recognition of patients colonized by the epidemic strain of C. diversus. Rectal and nasopharyngeal specimens were plated and incubated on MacConkey agar containing 10 micrograms of kanamycin per ml. After 18 h of incubation, lactose-nonfermenting colonies present on the selective medium were picked and identified 8 h later with the following biochemical tests: indole, adonitol, dulcitol, citrate, and triple sugar iron agar. This presumptive identification of C. diversus was later confirmed for all cases by conventional testing with a complete set of biochemicals. In 1 week, 253 specimens from patients were processed with this technique, and 49 strains of C. diversus were identified. The rapid identification of C. diversus and transfer of carriers into appropriate cohorts resulted in a 64% reduction in the prevalence of colonization.

Five infants born at one hospital over a two-year period developed meningitis due to a serotype O2 strain of Citrobacter diversus; four infants developed brain abscesses due to this organism. The initial prevalence of stool colonization in infants was 79%; eventually 140 infants (10%) and six nurses (6%) were found to be colonized. One colonized infant remained in the hospital for the entire two-year period. The strains were of two biotypes marked by the presence (biotype d) or absence (biotype a) of fermentation of sucrose and dulcitol. The biotype d strain was found in the five infants with meningitis, 110 asymptomatic infants, and five nurses. The biotype a strain, which was isolated from 30 infants and one nurse, did not cause disease. Colonized infants were distinguished by intensive care therapy (P = 10-31), gavage feeding (P = 0.036), and prenatal intrauterine monitoring (P = 0.037). These findings suggest a fecal reservoir and person-to-person transmission of C. diversus. Measures to control the outbreak cost about $110,000.