Summertime Bacillus cereus colonization of hospital newborns traced to contaminated, laundered linen

Background: Routine screening of premature newborns for haemolytic streptococci, Staphylococcus aureus and enteric Gram-negative bacteria done at birth using umbilical swabs identified clustering of babies colonized with Bacillus cereus in summers of 2009 and 2010 at a 400-bedded UK general hospital. Aim: To determine the source of this organism by focusing on the clinical environment. Methods: Umbilical swab screening was extended to all newborns and the labour ward environment, including construction-related dust, was sampled for B. cereus. Findings: During the summer of 2009, 65% of newborns had umbilical swabs which were culture positive for B. cereus. Blood agar and B. cereus selective agar impression plates of unused labour ward linen, and freshly received linen from the hospital's external laundry, gave mainly confluent growth of B. cereus in >85% of items sampled. In-use and exposed healthcare products including liquid handwashing agents, paper hand-towels, vaginal lubricants, labour ward dust and air were culture negative. Linen contamination and umbilical swab culture positivity both approached zero in autumn. B. cereus colonization of newborn umbilici recurred in summer 2010 and unused laundered linen was again found to be as contaminated. Washing linen at the laundry in a washer-extractor, with higher dilution than the continuous tunnel washer normally used, coincided with lowering of detectable B. cereus numbers in unused washed linen and no clustering in newborns the following summer (2011). Conclusion: Freshly laundered linen can be contaminated with B. cereus with subsequent spread and colonization of newborns. This contamination appears to be associated with low-dilution washing and high ambient temperatures.