ECDC unveils Seroincidence calculator for Salmonella and Campylobacter

Campylobacteriosis and salmonellosis are the two leading gastrointestinal diseases in the European Union.

The reported number of cases represents only a small fraction of all infections in human populations, said the agency.

One way to assess infections in humans is to measure antibody levels in serum collections, it added.

ECDC produces a yearly report with the European Food Safety Authority (EFSA) where it assess the latest data on foodborne outbreaks​.

Assessing the true burden​

Johanna Takkinen, head of the Food and Waterborne diseases and zoonoses program at ECDC, said because of infection going unnoticed or it being underreported it is difficult to assess real burden.

“One reason to continue a research project at EU level was to come up with a tool to estimate the burden of illness closer to true circulation of pathogens in human population,” ​she told FoodQualityNews.

“The representative numbers are only a tiny proportion of actual infections and there is a huge discrepancy​. It is a​ tool in a statistics package, it is not the general population who will use it but it is targeted at researchers or epidemiologists with the help of statisticians. ​

“It involves collecting serum from countries which might have different collection methods, then perform testing based on research and assess the frequency of exposure to pathogens in the sampled population.​

“Public health monitors the impact of the control measures, you can repeat in regular intervals, and compare results to better estimate circulation of pathogens.”  ​

How the tool works​

The seroincidence calculator tool​ uses the combination of serum antibody levels (IgG, IgM, and IgA) at a given time point to estimate the time since seroconversion, which gives an estimate of annual “force of infection” in the tested population.

Relationship between the three antibody levels and estimated time since infection (seroconversion) was established in previous longitudinal studies where lab-confirmed cases were followed up for several months and the decay of serum antibody levels were determined by indirect ELISA methods.

Antibody levels measured in a cross-sectional population sample can be translated into an estimate of the frequency with which seroconversions (infections) occur.

Surveillance issues​

Takkinen said using the tool can measure burden more objectively and is not dependant on other factors.

“Currently with surveillance there are lots of steps in place to get information to national and further to EU level. People get ill and do not see the doctor or the doctor gives them antibiotics and does not request a stool sample,” ​she said.

“Labs have to find the pathogen, which is usually not a problem, then the information must find its way in the surveillance system to national level and then us at EU level.​

“There are countries that report few cases but that can be because their system doesn’t capture them and some countries report high because the national surveillance system is good.​

“One could get an estimate and repeat the study, in say five years and see the impact of control measures in public health. ​

“For example, the reduction of Salmonella enteritidis in EU assumed mostly due action taken in laying hens and you need to have objective figures to measure whether the reduction is true.” ​

A Bayesian back-calculation model was used to convert antibody measurements into an estimation of time since infection. This can estimate seroincidence in the cross-sectional sample of population.

Seroincidence estimates are suitable for monitoring the effect of control programmes by providing more accurate information on the infection pressure in humans across countries.

To make functionalities as broadly available as possible, R was chosen as the computing platform, as it is free and open source.

R is a programming language and software environment for statistical computing and graphics.

It provides statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, etc.) and graphical techniques.

ECDC said the idea is the tool could be applicable to other pathogens and it is looking at Hepatitis.

Takkinen said food safety is a topic which touches multiple people.

“The economic situation can impact on a countries capability to perform tests on stool samples so results can be biased,” ​she said.

“Working together on days like this is invaluable as it touches every person and requires multi-sectorial collaboration as food trends change in the globalised world.” ​