Alaska is a top cruise ship destination, and summertime influenza outbreaks among Alaska-bound travelers are not uncommon. The state receives almost one million cruise ship passengers each summer, 1.5 times its wintertime population. Cruise ships carry upwards of 3,500 crew and passengers, representing numerous countries from the Northern and Southern Hemispheres on each voyage. These factors, in addition to close quarters and prolonged contact on ships, increase the transmission risk of communicable diseases such as influenza. They also provide an opportunity for the introduction of respiratory viruses to North America each summer.
The Alaska Cruise Ship Respiratory Surveillance Pilot Project is the first CDC-state partnership pilot project nationwide to introduce a laboratory component to routine cruise ship syndromic respiratory illness surveillance. It enables the detection of influenza viruses (including imported strains) and other respiratory viruses circulating among cruise ship travelers in Alaska and helps characterize the introduction risk of out-of-season influenza viruses into Alaskan and other U.S. communities.
METHODS:
Participating cruise ships worked with the CDC and the State of Alaska to collect respiratory specimens from crew and passengers who came to each ship’s infirmary with fever and respiratory symptoms during three cruise ship seasons (May 1 – Sept 30) from 2013 - 2015. These specimens were submitted for respiratory virus testing at the Alaska State Virology Laboratory and compared to land-based results. A subset of the influenza-positive specimens were also sent to CDC’s Influenza Division’s Laboratory for further characterization.
RESULTS:
Four hundred and seventeen specimens were analyzed from 14 cruise ships. Eighty-three percent (n=346) of the samples tested positive for at least one respiratory virus using the GenMark Respiratory Viral Panel. Of the positive specimens, 70% (n=241) contained influenza A, and 16% (n=56) contained influenza B. The remaining 14% (n=49) positive specimens contained at least one other respiratory virus. Additional findings included memory recall of previous year vaccinations among cruise ship passengers (57%) and crew (44%); and differences between influenza rates onboard cruise ships (71%) and on land (14%) during the same period.
CONCLUSIONS:
This project demonstrated the feasibility of conducting sentinel respiratory virus surveillance on cruise ships and enhanced the CDC’s and state’s ability to detect and monitor travel-related respiratory viruses. This sentinel respiratory virus surveillance system can be used to identify the possible introduction of out-of-season influenza viruses into U.S. communities where cruise ships disembark. The project also helped underscore the importance of crew and passenger vaccinations.