Cruise ship environmental hygiene and the risk of norovirus infection outbreaks: an objective assessment of 56 vessels over 3 years.

BACKGROUND Norovirus infection outbreaks (NoVOs) occur frequently in closed populations, such as cruise ship passengers. Environmental contamination is believed to play an important role in NoVO propagation. METHODS Trained health care professionals covertly evaluated the thoroughness of disinfection cleaning (TDC) of 6 standardized objects (toilet seat, flush handle or button, toilet stall inner handhold, stall inner door handle, restroom inner door handle, and baby changing table surfaces) with high potential for fecal contamination in cruise ship public restrooms, by means of a previously validated novel targeting method. RESULTS Fifty-six cruise ships (approximately 30% of 180 vessels operated by 9 large cruise lines) were evaluated from July 2005 through August 2008. Overall, 37% (range, 4%-100%; 95% confidence interval, 29.2%-45.4%) of 8344 objects in 273 randomly selected public restrooms were cleaned daily. The TDC did not differ by cruise line and did not correlate with the Centers for Disease Control and Prevention (CDC) Vessel Sanitation Program inspection scores (r(2), .002; P = .75). More than half the vessels had overall TDC scores <30%, although several of these low-scoring ships had near-perfect CDC sanitation scores. The mean TDC of the 3 ships evaluated within 4 months before a NoVO (10.3%) was substantially less than the mean TDC of the 40 ships that did not experience NoVOs (40.4%) (P < .004). CONCLUSIONS An objective evaluation of public restroom environmental hygiene on 56 cruise ships found that only 37% of selected toilet area objects were cleaned on a daily basis. Low TDC scores may predict subsequent NoVO-prone vessels. Enhanced public restroom cleaning may prevent or moderate NoVOs on cruise ships.