Massive hospital-wide bacillus outbreak related to hospital linen and construction

Abstract

Introduction / objectives: At the National University Hospital in Singapore, the baseline average number of bacillus cultures/month is eight. An outbreak became evident when 274 clinical isolates of Bacillus were recovered from 230 inpatient episodes between April and August 2010. An investigation was undertaken. Methods: Chart reviews of affected patients and extensive environmental sampling was followed by a review of hospital ventilation systems, cleaning protocols and laundry processes. Response to interventions was monitored via clinical case numbers and environmental sampling over a six month period. Results: B. cereus complex constituted 164 cases (71.3%). Bacteraemia comprised 207 patient episodes (90.0%), of which 124 occurred in immunocompromised patients or those with intravascular devices. Physicians treated the organism in 68 episodes (29.5%). Environmental investigations confirmed heavy air contamination particularly within patient rooms and air conditioned wards. Dense airborne contamination outside the hospital adjacent to large earthworks on a construction site was demonstrated (~600CFU/m3). Towels were heavily contaminated even after laundering (7403+/-1054 spores/cm2). Amplification of spores occurred in clean linen due to storage conditions (165+/-84 spores/cm2 pre-storage vs 4437+/-1228 spores/cm2 post-storage). Interventions focusing on laundry protocols, environmental cleaning and air filtration saw clinical case numbers return to baseline levels within three months. Conclusion: Environmental contamination with Bacillus may be an underrecognised infection risk in hospitals exposed to construction work. Laundering and environmental cleaning processes that are not sporicidal carry a greater risk. Storage conditions of cleaned linen can amplify Bacillus contamination.