The method was developed by researchers at Statens Serum Institut in Denmark and colleagues in the Netherlands and is called seroincidence.
In 2013 there were 1,132 cases of Salmonella infection in Denmark. It was roughly the same in 2012 and 2011 and is equivalent to about 22 per 100,000 inhabitants in the country.
Lowest in Sweden, highest in Spain
Seroincidence is not a measure of clinical illness and does not find its actual burden.
It attempts to measure the frequency of exposures to Salmonella that are recognized by the immune system and followed by antibody response.
The annual seroincidence of Salmonella ranged from 0.056 infections per person-year in Sweden to 0.61 in Spain, said the study.
Researchers found a 10-fold difference in the annual incidence of infections when comparing estimates from Spain (0.61) and Poland (0.55) with the Nordic countries (Sweden 0.06, Finland 0.07 and Denmark 0.08).
One reason behind this could be these countries have extensive Salmonella control programs in food animals, said Kåre Mølbak from the Statens Serum Institut.
“The method calculates the risk of a person becoming infected and not the diseases,” he told FoodQualityNews.
“There is a much higher risk in Spain than in Sweden as there has been a focus a lot on Salmonella in eggs and pork in the Nordic countries which means a substantially lower risk of infection.”
The seroincidence is calculated from analysis of the levels of antibody classes against nontyphoid salmonellae in the general population, and results are converted into a single metric based on antibody decay, said the researchers.
Seroepidemiology is well suited to evaluate the impact of control programs in food animals on the Salmonella incidence in the human population, they added.
Seroincidence was estimated based on the antibody decay profile found in a longitudinal study of Danish patients with culture-confirmed Salmonella gastroenteritis.
13 countries estimated
Estimates from the Netherlands, England, Austria, and Ireland ranged from 0.095 to 0.164.
From Greece, Italy, Romania, France, Poland, and Spain they ranged from 0.20 to 0.61.
Mølbak said the model, which has attracted interest from the US and the Netherlands, is at the research stage.
“No decision has been made to implement it in routine, which is where we hope it will lead us, that requires the food authority to accept it,” he said.
“We hope it will have an end result to reduce the risk of infection, it is an objective way of measuring as the method now depends a lot on laboratory practices and hospitals which differ between EU countries.”
Researchers developed a model that enabled back-calculation of annual salmonellosis seroincidence from measurements of Salmonella antibodies and applied it to 9,677 serum samples from 13 European countries.
Numbers were correlated with prevalence data of Salmonella in laying hens, broilers and slaughter pigs and not reported national incidence of infections.
“We do not know how many of the seroincident infections are cases with clinical disease,” said the researchers.
“A 10-fold difference in seroincidence between Sweden and Spain, in other words, does not necessarily pan out as a 10-fold difference in burden of illness.”
Austria, England, Greece, Ireland, Spain, and the Netherlands (2006–2007) provided serum sample collections.
Data was recalculated from a published study in Denmark, Finland, France, Italy, the Netherlands (1998–2002), Romania, Poland, and Sweden.
Source: Clinical Infectious Diseases
Online ahead of print, DOI: 10.1093/cid/ciu627
“Seroincidence of Human Infections With Nontyphoid Salmonella Compared With Data From Public Health Surveillance and Food Animals in 13 European Countries”
Authors: Kåre Mølbak, Jacob Simonsen, Charlotte S. Jørgensen, Karen A. Krogfelt, Gerhard Falkenhorst, Steen Ethelberg, Johanna Takkinen and Hanne-Dorthe Emborg