Between July and September of 2009, health officials in Hungary noted an unusually high number of Salmonella Goldcoast infections in the country. In October, they sent an inquiry to Europe’s disease tracking system to see whether this rare strain of Salmonella had surfaced in any other countries. The results showed that Italy too had seen a spike in Salmonella Goldcoast infections that fall, and cases had been reported in Denmark, Norway, Spain and the United Kingdom. In this week’s issue of Eurosurveillance, two articles chronicle the Hungarian and Italian investigations into the 2009 S. Goldcoast outbreaks, which predominantly affected these two countries. The findings of the two investigations strongly suggest a link between the two outbreaks. Both teams pinpointed contaminated pork as the most likely outbreak source, and the DNA fingerprint of the strain responsible for the Hungarian outbreak was a 90 percent match to the strain tied to the Italian outbreak. However, epidemiologists were unable to pinpoint a specific food source common to both outbreaks. The Outbreaks In Hungary, a total of 44 patients with matching strains of Salmonella Goldcoast were eventually identified, with illness onset dates ranging from July of 2009 and January of 2010. One product that registered as a statistically significant common food among victims was pork cheese, eaten by nine of the victims for whom information was available. One S. Goldcoast sample was recovered from a sample of minced beef that originated at a slaughterhouse where pigs were also slaughtered, according to investigators. Another piece of evidence linking the S. Goldcoast infections to pork products was the fact that “recent data from Salmonella surveys in pig holdings throughout the EU suggest that S. Goldcoast is one of the most common serotypes identified in pig breeding and production holdings outside Hungary,” say the authors of the Hungarian investigation report, referring to an analysis of a survey of Salmonella presence in EU pig breeding pens from the European Food Safety Authority. “This last piece of information allows us to hypothesise that, rather than a single contaminated food item, pigs from a number of holdings were contaminated, partly exported to other countries where they were raised and slaughtered and released to the national markets during several months,” says the report. In Italy, 79 cases of S. Goldcoast infection were identified between June of 2009 and March of 2010. Of these, 17 cases were linked to three outbreaks, while the others were considered sporadic. Among the 39 patients with sporadic cases that were interviewed, 20 reported eating salami prior to illness. The closely related S. Goldcoast strains found in patients in Italy were also “highly similar to S. Goldcoast strains that had been isolated in Italy from pigs and pork-containing food items in 2009 and 2010,” according to the investigation report. “Our investigation revealed that a community-wide outbreak of S. Goldcoast probably associated with a continuous source of infection occurred in Italy between 2009 and 2010,” concludes the summary of the Italian investigation. “It cannot be excluded that the real burden of this outbreak and its geographical distribution were wider than what was identified.” This inability to find the root of what might have been widespread contamination from a single source points to the need for a coordinated disease surveillance effort across Europe, say two top officials at the European Centre for Disease Prevention and Control (ECDC) in an editorial published alongside the two outbreak reports in Eurosurveillance. “The two articles highlight challenges in the investigation of potential cross-border multi-country outbreaks where multiple contaminated vehicles originating from the similar type of food production chain may serve as a source of infection of sporadic cases and may cause point source outbreaks at local, regional or national level,” writes Denis Coulombier, head of the Unit for Surveillance and Response Support at ECDC and Johanna Takkinen, coordinator of ECDC’s Programme on Food- and Waterborne Diseases and Zoonosis. One way to narrow down potential sources in complex outbreaks such as these is to investigation household outbreaks, suggest the authors. Finding common food exposures among victims in these smaller environments can offer clues about what foods to flag in an investigation. “Even though often small and limited, household outbreaks may reveal a common exposure to pork meat or a single vehicle in a family cluster and family clusters may indicate the presence of contaminated raw food of animal origin on the retail market,” note the authors. Indeed over half of Salmonella outbreaks with strong evidence of a source occurred in single households in 2010, according to the European Food Safety Authority. Coulombier and Takkinen also highlight the need for sharing information across sectors: “The two S. Goldcoast outbreaks stress the importance of collaboration between public health and veterinary authorities and the need to share samples and data from human, animal, food and feed across sectors when investigating such complex outbreaks.” One way information can be better shared is through standardizing the way pathogens are profiled, so that they can be easily shared by labs and compared to one another, suggest the writers. The EU launched a pilot project in November of 2012 designed to overcome this problem by facilitating the rapid sharing of molecular data.