Acute Gastroenteritis on Cruise Ships - Maritime Illness Database and Reporting System, United States, 2006-2019.

Problem/condition: Gastrointestinal illness is common worldwide and can be transmitted by an infected person or contaminated food, water, or environmental surfaces. Outbreaks of gastrointestinal illness commonly occur in crowded living accommodations or communities where persons are physically close. Pathogens that cause gastrointestinal illness outbreaks can spread quickly in closed and semienclosed environments, such as cruise ships. CDC's Vessel Sanitation Program (VSP) is responsible for conducting public health inspections and monitoring acute gastroenteritis (AGE) illness on cruise ships entering the United States after visiting a foreign port.

Period covered: 2006-2019.

Description of system: VSP maintains the Maritime Illness Database and Reporting System (MIDRS) for monitoring cases of AGE illness among passengers and crew sailing on cruise ships carrying ≥13 passengers and within 15 days of arrival at U.S. ports from foreign ports of call. Cruise ships under VSP jurisdiction are required to submit a standardized report (24-hour report) of AGE case counts for passengers and crew 24-36 hours before arrival at the first U.S. port after traveling internationally. If the cumulative number of AGE cases increases after submission of the 24-hour report, an updated report must be submitted no less than 4 hours before the ship arrives at the U.S. port. A special report is submitted to MIDRS when vessels are within 15 days of arrival at a U.S. port and cumulative case counts reach 2% of the passenger or crew population during a voyage. VSP declares an outbreak when 3% or more of the passengers or crew on a voyage report AGE symptom to the ship's medical staff.

Results: During 2006-2019, a total of 37,276 voyage reports from 252 cruise ships were submitted to MIDRS. Of the 252 cruise ships, 80.6% were extra large in size (60,001-120,000 gross registered tons [GRT]), 37.0% and 32.9% had voyages lasting 3-5 days and 8-10 days, respectively, and 53.2% were traveling to a port in the Southeast region of the United States at the time the final MIDRS report was submitted. During 2006-2019, VSP received 18,040 (48.4%) 24-hour routine reports, 18,606 (49.9%) 4-hour update reports, and 612 (1.6%) special reports (2% and 3% AGE reports). Incidence rates decreased from 32.5 cases per 100,000 travel days to 16.9 for passengers and from 13.5 to 5.2 for crew. Among passengers, AGE incidence rates increased with increasing ship size and voyage length. For crew members, rates were significantly higher on extra-large ships (19.8 per 100,000 travel-days) compared with small and large ships and on voyages lasting 6-7 days. Geographically, passenger incidence rates were highest among ships underway to ports in California, Alaska, Texas, New York, Florida, and Louisiana. Among passengers, AGE incidence rates were significantly higher on ships anchoring in California (32.1 per 100,000 travel-days [95% confidence interval (CI) = 31.7-32.4]); among crew, they were significantly higher in the South region of the United States (25.9 [CI = 25.1-26.7]).

Interpretation: This report is the first detailed summary of surveillance data from MIDRS during 2006-2019. AGE incidence rates decreased during this time. Incidence rates among passengers were higher on mega and super-mega ships and voyages lasting >7 days. AGE incidence among crew was higher on extra-large ships and voyages lasting 6-7 days. Ship size and voyage length are associated with AGE incidence rates, and more targeted effort is needed to prevent disproportionate AGE incidence rates among passengers and crew sailing in high-risk situations.

Public health actions: Maritime AGE surveillance provides important information about the epidemiology of gastrointestinal illness among cruise ship populations traveling in U.S. jurisdictions. AGE illness is highly contagious and can be transmitted quickly within vessels. State and local public health departments in the United States can use data in this report to better inform the traveling public about the risk for AGE and the importance of their role in minimizing the risk for illness while traveling onboard cruise ships. Key elements for reducing exposure to AGE illness, limiting the spread of illness, and preventing AGE outbreaks are proper hand hygiene practices and prompt isolation of symptomatic persons. Passengers can work in collaboration with cruise lines to promote onboard public health by frequently washing their hands, promptly reporting AGE illness symptoms, and isolating themselves from other persons immediately after illness onset. Access to and proper use of handwashing stations can reduce the risk for illness transmission aboard cruise ships.