This study describes a gastrointestinal outbreak which occurred on a US Navy ship in the port of Callao, Peru. Although NoV GI and ETEC were both identified as etiological agents in the early phase of the outbreak, it is likely that NoV was the source of the outbreak in the secondary wave based upon its mechanism of transmission. Retrospective investigations have identified NoV GI as the cause of outbreaks and single infections among populations of several South and Central American countries 
, including a recent extensive outbreak which occurred in Antofagasta, Chile 
. This is the first description of an outbreak related to infection with NoV GI in Peru and, to our knowledge, the first outbreak of NoV reported on a US naval ship in South America. With the exception of one study conducted in Denmark, outbreaks linked to dual infections of NoV and ETEC have been limited and poorly described 
. Although we were unable to collect control samples, which may have helped to better define the role of ETEC in this outbreak, our data suggests NoV was likely the primary cause of illness in the later cases due to its short incubation period and daily presentation of new cases several days after leaving port, suggesting person-to-person transmission. Unlike NoV, there is some evidence suggesting that ETEC is not readily transmitted via fomites 
, this may be due to a shorter half-life of the pathogen in the environment. However, ETEC and NoV have been shown to be co-associated in individuals with diarrhea and among cases in outbreaks 
. The dual role of these pathogens in outbreaks and illness should be carefully evaluated in future investigations.
NoV infection is a frequent cause of diarrhea and vomiting among travelers to developing countries 
and has been widely recognized as an important cause of outbreaks on US military and civilian ships 
. Although outbreaks on US Navy ships are not typically associated with visits to high-risk ports for traveler's diarrhea 
, our findings demonstrate that NoV has the potential to be introduced into a ship following personnel visits to a foreign port during deployed missions. Precautions among the ship's personnel (i.e., health education on food safety and proper food and hand hygiene) should be reinforced prior to entering port cities. Precautions should also include avoiding the consumption of beverages prepared with unknown source water, including ice, during these visits. The protective role of consuming bottled water observed in our study may have been related to individuals who were less likely to engage in risky behaviors such as ingestion of uncooked foods or poor hand hygiene, both of which are known to be linked to and propagate food-borne outbreaks. Personnel should be encouraged to drink only bottled beverages, consume thoroughly washed or cooked foods and routinely wash their hands prior to eating.
In this outbreak, the primary infection (i.e., index case(s)) likely occurred during their visit to a specific area in Lima, with subsequent person-to-person and fomite transmission (i.e., hand rails, bunks, etc.). Although the initial disinfection of the ship probably removed the majority of the surface contamination, repeated contamination of these surfaces likely occurred, as 28% of the crewmembers were symptomatic and moving throughout the ship. Persistence of NoV is among the most significant contributing factors for shipboard outbreaks, as surfaces can remain contaminated for lengthy periods of time facilitating transmission of the infection to naïve individuals. Thus, various prevention measures should be considered to minimize dissemination of this virus during shipboard outbreaks. Such measures may include, a shipboard outbreak response program which could allow implementation of rapid and effective control measures during gastrointestinal outbreaks (i.e., proper disinfection guidelines), informational materials providing symptomatic individuals with guidance on personal hygiene and recommendations on temporary self-isolation/movement restriction, informational materials for asymptomatic individuals on how to prevent illness during an outbreak (i.e., hand hygiene, etc.) and installation of alcohol hand gel dispensers in key locations. Finally, surveillance and identification of gastrointestinal viruses, including NoV GI, during gastrointestinal outbreaks and among individuals suffering from gastrointestinal illness should be considered, to better define the epidemiology and burden of illness caused by these viruses and their interaction with other pathogens (e.g., ETEC) in developing countries, particularly in South America.