Researchers from National University Hospital in Singapore report on an investigation undertaken when the baseline average number of bacillus cultures per month escalated from eight to 274 clinical isolates recovered from 230 inpatient episodes between April and August 2010.
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 percent). Bacteraemia comprised 207 patient episodes (90.0 percent), of which 124 occurred in immunocompromised patients or those with intravascular devices. Physicians treated the organism in 68 episodes (29.5 percent). 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.
The researchers conclude that environmental contamination with Bacillus may be an underrecognized infection risk in hospitals exposed to construction work. They add that laundering and environmental cleaning processes that are not sporicidal carry a greater risk, and that storage conditions of cleaned linen can amplify Bacillus contamination. Their research was presented at the International Conference on Prevention & Infection Control (ICPIC) held in Geneva, Switzerland June 29-July 2, 2011.
Reference: M Balm, C Teo, R Jureen, R Lin, D Fisher. Massive hospital-wide bacillus outbreak related to hospital linen and construction. Presentation at International Conference on Prevention & Infection Control (ICPIC). BMC Proceedings 2011, 5(Suppl 6