Outbreak of Bacillus cereus infections in a neonatal intensive care unit traced to balloons used in manual ventilation

Abstract

In 1998, an outbreak of systemic infections caused by Bacillus cereus occurred in the Neonatal Intensive Care Unit of the University Hospital Vrije Universiteit, Amsterdam, The Netherlands. Three neonates developed sepsis with positive blood cultures. One neonate died, and the other two neonates recovered. An environmental survey, a prospective surveillance study of neonates, and a case control study were performed, in combination with molecular typing, in order to identify potential sources and transmission routes of infection. Genotypic fingerprinting by amplified-fragment length polymorphism (AFLP) showed that the three infections were caused by a single clonal type of B. cereus. The same strain was found in trachea aspirate specimens of 35 other neonates. The case control study showed mechanical ventilation with a Sensormedics ventilation machine to be a risk factor for colonization and/or infection (odds ratio, 9.8; 95% confidence interval, 1.1 to 88.2). Prospective surveillance showed that colonization with B. cereus occurred exclusively in the respiratory tract of mechanically ventilated neonates. The epidemic strain of B. cereus was found on the hands of nursing staff and in balloons used for manual ventilation. Sterilization of these balloons ended the outbreak. We conclude that B. cereus can cause outbreaks of severe opportunistic infection in neonates. Typing by AFLP proved very useful in the identification of the outbreak and in the analysis of strains recovered from the environment to trace the cause of the epidemic.

FIG. 1

Genotypic fingerprints. Digitized AFLP patterns and dendrogram of a selection of B. cereus isolates. The dendrogram was constructed using Gelcompar cluster analysis by unweighted pair group method using average linkages. Percentages of similarity and molecular sizes are shown on top of the figure. The cut-off value for identical strains is 85%. Abbreviations: I, neonate infected by B. cereus; patient number corresponds with those used in Table 1; B, balloon used in mechanical ventilation; C, neonate asymptomatically colonized with B. cereus in the respiratory tract; N, nursing staff from NICU (N.1 to N.5) and another ward (N.6); culture of print of dominant hand; R, reference strain; D, dust on baseboard in the NICU.

FIG. 2

Percentage of newly admitted mechanically ventilated neonates who became colonized with B. cereus in the respiratory tract between January 1997 and January 1999. Balloons were sterilized by autoclaving starting from 14 July 1998. For January 1997 to January 1998, numbers were determined retrospectively by review of laboratory work sheets. For February 1998 to January 1999, numbers were prospectively determined. Jan, January; Jul, July.