Laboratory-based respiratory virus surveillance pilot project on select cruise ships in Alaska, 2013-15.

BACKGROUND: Influenza outbreaks can occur among passengers and crews during the Alaska summertime cruise season. Ill travellers represent a potential source for introduction of novel or antigenically drifted influenza virus strains to the United States. From May to September 2013-2015, the Alaska Division of Public Health, the Centers for Disease Control and Prevention (CDC), and two cruise lines implemented a laboratory-based public health surveillance project to detect influenza and other respiratory viruses among ill crew members and passengers on select cruise ships in Alaska. METHODS: Cruise ship medical staff collected 2-3 nasopharyngeal swab specimens per week from passengers and crew members presenting to the ship infirmary with acute respiratory illness (ARI). Specimens were tested for respiratory viruses at the Alaska State Virology Laboratory (ASVL); a subset of specimens positive for influenza virus were sent to CDC for further antigenic characterization. RESULTS: Of 410 nasopharyngeal specimens, 83% tested positive for at least one respiratory virus; 71% tested positive for influenza A or B virus. Antigenic characterization of pilot project specimens identified strains matching predominant circulating seasonal influenza virus strains, which were included in the northern or southern hemisphere influenza vaccines during those years. Results were relatively consistent across age groups, recent travel history, and influenza vaccination status. Onset dates of illness relative to date of boarding differed between northbound (occurring later in the voyage) and southbound (occurring within the first days of the voyage) cruises. CONCLUSIONS: The high yield of positive results indicated that influenza was common among passengers and crews sampled with ARI. This finding reinforces the need to bolster influenza prevention and control activities on cruise ships. Laboratory-based influenza surveillance on cruise ships may augment inland influenza surveillance and inform control activities. However, these benefits should be weighed against the costs and operational limitations of instituting laboratory-based surveillance programs on ships.

Passenger behaviors associated with norovirus infection on board a cruise ship--Alaska, May to June 2004.

BACKGROUND: During May 2004, the Vessel Sanitation Program (VSP) investigated an outbreak of norovirus gastroenteritis on board a cruise ship sailing in Alaska waters. The objectives were to identify a common food item source and explore behavioral risk factors for person-to-person transmission among passengers. METHODS: A case was defined as three or more episodes of loose stools within 24 hours or two or fewer episodes of loose stools accompanied by one or more episodes of vomiting. Vomitus and stool samples from affected passengers were tested for norovirus by reverse transcriptase-polymerase chain reaction. Environmental health officers performed an environmental investigation following VSP protocol. Questionnaires about food items consumed and behavioral risk factors were placed in cabin mailboxes (n = 2,018). A case-control study design using multivariable logistic regression tested associations between risk factors and disease. RESULTS: A total of 359 passengers (24.1% of respondents) met the case definition. Four of seven clinical specimens tested positive for norovirus. No significant deficiencies in environmental health practices were identified, and no meal servings were associated with disease. Having a cabin mate sick with diarrhea or vomiting [odds ratio (OR): 3.40; 95% confidence interval (CI) = 1.80-6.44] and using a specific women's toilet that was contaminated with vomit (OR: 5.13; 95% CI = 1.40-18.78) were associated with disease. Washing hands before meals was protective (OR: 0.25; 95% CI = 0.12-0.54) against disease. CONCLUSIONS: Widespread person-to-person norovirus outbreaks can occur on board cruise ships, even with appropriate environmental health practices. Programs to prevent and control norovirus outbreaks on board cruise ships should involve strategies that disrupt person-to-person spread and emphasize hand washing.