Gastrointestinal 'Spikes' Before and After GI Outbreaks

After reviewing gastrointestinal illness on approximately 21,000 cruises over a eight-year period, Disease Strategies found that many passenger based gastrointestinal outbreaks are preceeded by 'spikes' of symptomatic illness in either the crew or passenger populations on previous voyages. This temporal relationship is easily seen by viewing the "Trend Chart" of any cruise ship on this website.

While gastrointestinal germs are common in hospital and nursing home environments, cruise ships are also perfect incubators for these germs unless proactive cleaning measures are not strictly adhered to on a daily basis to minimize the risks associated with highly contagious diseases, such as the Norovirus germ.

Frequently, the CDC VSP program many times blames an outbreak on one sick passenger that boards a ship on the first day of a voyage. But, knowing the etiology of gastrointestinal disease and other factors relating to cruise ship processes combined with crew and passenger population interactions, several important components remain the same across sequential cruises.

Depending on the voyage, these components may include (1) common ship areas that may be contaminated with disease; (2) symptomatic crew members that may be exhibiting signs of illness; and (3), most importantly, asymptomatic crew members not showing signs of the disease. After contracting the illness, any passenger or crewmember can spread GI Illness for up to two weeks after symptoms has disappeared through 'fecal shedding'.

Simply put, contagious germs left over by passengers or crew from previous voyages are as likely, or even more likely, to cause outbreaks on successive cruises as one or more sick passengers that embarked on the voyage with the actual outbreak—as the CDC VSP often reports to the general public. To verify this information yourself, open any of the trend charts for each cruise ship on this website.

When this project began in 2003, the original intent was to create a computer program that assists cruise ship physicians in real-time analysis of gastrointestinal illness on cruise ships. Through the use of this real-time information, the physician could advise the ship captain when gastrointestinal illness was on the rise.

In theory, this early-warning system would enable the ship staff to perform emergency cleaning to help reduce the incidence of transmittable infections before it becomes an actual outbreak. To accomplish this goal, a series of statistical tools to analyze cruise ship illness on each voyage were designed, historical data was obtained from the CDC, and the results became clear.

When analyzing the data, the researchers found unexpected results that were simply amazing! In hindsight, we understand why the CDC made it so difficult for the research team to obtain the the cruise ship gastrointestinal illness data. Because of these data acquisition issues, the process of obtaining GI data caused these researchers to take the role of government health auditors to ensure the validity and completeness of the information being released into the public domain.

Commentary

The CDC Vessel Sanitation Program provides cruise ship owners little incentitive to proactively practice higher levels of risk management. Being a non-regulatory group within the CDC, the Vessel Sanitation Program can only 'recommend' what cruise lines should do to minimize the spread of gastrointestinal disease as they do not have authority or power to 'fine' them for not adhering to strict regulations (they are called guidelines).

Both the Vessel Sanitaiton Program and cruise line management are aware of the costs associated with practicing proactive GI disease risk management on a continuing basis and a long time ago the cruise lines decided it's better to practice reactive measures to illness.

It's also interesting that the CDC's own epidemiologists performed a study in 2004 that proves that there is absolutely no correlation between the CDC's inspection scores and Gastrointestinal Illness on cruise ships. Yet, emphasis public awareness of cruise ship inspection scores are paramount—rather than the actual incidence of passengers and crew members that take sick on each cruise. This information can only be found on this web site.

Unlike hospitals that must report contagious disease information in a public forum on a continuing basis, the CDC Vessel Sanitation Program only releases disease information that reaches an arbitrary threshold at or above 3%, sometimes as many as 90 passengers, before reporting a single case publically, then resets the counter for each and every voyage. In this case, the CDC's health policy is a two-pronged sword—it helps cruise lines' bottom line and effectively increases the overall level of gastrointestinal illness.