By Professor John Crump
The World Health Organization (WHO) Foodborne Diseases Epidemiology Group (FERG) has just published its much-anticipated first estimates of the global burden of disease related to contaminated food. The findings are startling: every year foodborne diseases cause one in 10 people worldwide to fall ill, 33 million healthy life years to be lost and 420,000 deaths, with a third of these among children less than five years of age.
I had the privilege of serving as FERG Resource Advisor on invasive Salmonella infections for the group working on bacterial, protozoal, and viral diseases.
This assignment presented an interesting methodological challenge, as burden of disease efforts typically start with the number of illnesses and deaths associated with a particular syndrome grouping or ‘envelope,’ and then assign these illnesses and deaths to individual pathogens causing that syndrome. In that respect, the diarrhoeal disease ‘envelope’ was the logical starting point for FERG.
However, illnesses and deaths due to some foodborne diseases like invasive Salmonella infections, including typhoid and paratyphoid fevers and invasive nontyphoidal Salmonella disease, as well as brucellosis and listeriosis, present with fever rather than diarrhoea.
Furthermore, there is no syndrome grouping or ‘envelope’ for febrile illnesses in the current global burden of diseases framework.
Instead, we had to take another approach, involving finding pathogen-specific studies of disease incidence, complications and deaths, and develop methods for extrapolating these data to parts of the world where such data were not available.
We had undertaken such efforts previously for typhoid and paratyphoid fevers. However, because nontyphoidal Salmonella disease presents primarily as a diarrhoea disease in industrialised countries, the frequently fatal invasive form of the disease so common among children in Africa and HIV-infected adults had been overlooked.
Consequently, we made the first estimate of the global burden of invasive nontyphoidal Salmonella disease earlier this year. We found that approximately 3.4 million cases of invasive nontyphoidal Salmonella disease occurred in 2010 and, with the sobering case fatality ratio of 20%, there were approximately 681,000 deaths.
Although the WHO FERG estimate only includes cases of invasive nontyphoidal Salmonella disease thought to be transmitted by food and not associated with HIV-infection, it is gratifying that a major killer of African children can now be recognised in the global accounting of causes of illness and death. This is the first step in making the case for investments in prevention and treatment. (Waterborne transmission is likely to be important too, but modes of transmission have not been well studied in Africa.)
In an effort to support disease control efforts and improve opportunities for meat producers, the Livestock, Livelihood, and Health project called Hazards Associated with Zoonotic enteric pathogens in Emerging Livestock meat pathways (HAZEL) is attempting to understand how nontyphoidal Salmonella and Campylobacter move through meat production from the farm to retailers in Tanzania.
The project is coming to the end of its first year of activities. During the coming two years we hope to shed new light on these pathogens in meat production in East Africa and make a contribution to eventually addressing these important infections.
Professor John Crump is the inaugural McKinlay Chair of Global Health at the Dunedin School of Medicine, University of Otago.
WHO estimates of the global burden of foodborne diseases Foodborne diseases burden epidemiology reference group 2007-2015