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.
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.
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.
Environmental contamination with Bacillus may be an under-recognised 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.
Disclosure of interest