Researchers forecasted the number of cases of salmonellosis, campylobacteriosis and listeriosis from 2012 to 2020 and calculated the corresponding number of disability-adjusted life years (DALYs).
The DALY metric quantifies the burden of a disease as the number of healthy years of life lost to morbidity and mortality.
The work found burden of campylobacteriosis could increase by a factor of almost two by 2020 from 2012.
Burden of salmonellosis will remain stable between 2012 and 2020 and that of listeriosis remained stable between 2012 and 2014.
“Efforts to control cases of salmonellosis and listeriosis in Belgium must be maintained in the future whereas new actions are urgently needed to understand and reduce the risk of food being contaminated with Campylobacter spp,” said researchers.
Prediction models used
The Belgian Scientific Institute of Public Health (WIV-ISP) collects data on laboratory-confirmed salmonellosis, campylobacteriosis and listeriosis cases.
Cases per month were available from January 2001 to December 2012 for salmonellosis, from January 1993 to December 2013 for campylobacteriosis and from January 2011 to December 2013 for listeriosis.
The work included all reported cases of campylobacteriosis and salmonellosis without distinguishing the origin of the infection, i.e. not all were caused by contaminated food.
Salmonellosis time series was fitted with a Bai and Perron two-breakpoint model, while a dynamic linear model was used for campylobacteriosis and a Poisson autoregressive model for listeriosis.
Average monthly number of cases of salmonellosis was 264 in 2012 and predicted to be 212 in 2020; campylobacteriosis cases were 633 in 2012 and 1,081 in 2020 and listeriosis numbers were five in 2012 and six in 2014.
After applying correction factors, the estimated DALYs for salmonellosis were 102 (95% uncertainty interval (UI): 8–376) in 2012 and predicted to be 82 (95% UI: 6–310) in 2020.
Visual inspection of the salmonellosis time series showed a downward trend after 2006 and strong seasonality.
“We observed a strong autoregressive model with seasonality, there were relatively more salmonellosis cases from June to August than in other months, and a statistically significant positive trend during the period January 2001 to November 2003.
“In the last period from November 2005 to December 2013, a new equilibrium was reached after the drop brought by the changes in vaccination and hygiene policies.”
Campylobacteriosis DALYs were 1,019 (95% UI: 137–3,181) and 1,736 (95% UI: 178–5,874).
Visual inspection of this time series showed a time-varying behaviour and strong seasonality.
Listeriosis DALYs were 208 (95% UI: 192–226) in 2012 and 252 (95% UI: 200–307) in 2014.
Outcome trees and transition probabilities were based on those suggested by the European Centre for Disease Prevention and Control (ECDC).
A major limitation of prediction models is they assume the environment and context will stay stable, said the researchers.
“Changes in knowledge about safe food handling, physician testing practices, new public health or animal health interventions or future outbreaks could all violate this assumption, but are impossible to predict,” they said.
“Second, we did not include food attribution percentages in the burden estimates, which means that some campylobacteriosis, salmonellosis and listeriosis cases may have been attributed to other sources of contamination than the consumption of contaminated food.
“Third, potential clustering of salmonellosis, which is more common compared with the other two diseases, was not taken into account in the times series analysis.”
Source: Eurosurveillance, Volume 22, Issue 38, 21 September 2017