Returning travellers could highlight emerging infections worldwide

Though picking up a Salmonella infection abroad could ruin your holiday, reporting it to your doctor could help detect emerging infections in tourist destinations, according to an article published today in BMC Medicine. A comprehensive database containing details of the infections that travellers pick up could help inform countries that have limited surveillance systems about possible disease outbreaks.

In Sweden, all reported cases of Salmonella infection must be entered into the Swedish Infectious Disease Register, detailing the type of bacteria that caused the infection and the place where the infection was contracted. Karin Nygård and her colleague used this database to assess whether there had been any changes in the numbers or types of Salmonella infection from different geographical regions between 1997 and 2002.

Their analyses of 13,271 cases of Salmonella infection in Swedes showed that 87% of these infections were contracted abroad. Most infections were reported from Spain, Greece and Turkey, mainly reflecting the popularity of these travel destinations for Swedish charter tourism.

The researchers also spotted that the numbers of diagnoses of a previously rare type of Salmonella Enteritidis, known as phage type (PT) 14b, increased dramatically among visitors to Greece during 2001.

PT14b became the third most common type of Salmonella in returning Swedish travellers in 2001, accounting for almost 13% of cases compared with only 2% in the previous four years. This rise may reflect an outbreak caused by a widely distributed contaminated food product in the region, or it may be because PT14b changed at some point during this year, becoming more widespread in the environment.

Dr Nygård believes that if information about increasing infection rates, or new strains of Salmonella, such as this, were communicated rapidly to the affected countries, those countries would be able to swiftly launch investigations into the outbreak and implement appropriate control measures to minimise the spread of infection.

According to the authors, travellers make a good “sentinel system” for infectious disease monitoring, as “people returning from travel abroad may have a higher tendency to seek medical care, and have a stool sample taken if an imported infection is suspected. In addition, visitors may be more susceptible to pathogens circulating in the community than local inhabitants.”

However, to be most useful, the data collected from many different countries about infections contracted abroad need to be pooled in order to create a comprehensive infectious diseases database. However, at present, many countries do not collect information on travel history in their surveillance of infectious diseases.