Sarah O'Brien, Professor of Epidemiology and Zoonoses, from Liverpool University's Institute of Infection and Global Health said the relationship between vaccination programs and the reduction in human disease is “compelling”.
Between 1992 and 2008, foodborne salmonella outbreaks reported to national surveillance fell from nearly 150 per year to just over 20 annually, and the pattern of decline closely mirrors that of laboratory-confirmed cases, according to Gormley et al.
Between 1981 and 1991, the number of salmonella infections rose by 170% in the UK, driven primarily by an epidemic of Salmonella Enteritidis which peaked in 1993.
When Salmonella Enteritidis PT4 peaked in 1993 in the UK, >18,000 laboratory-confirmed cases of illness were recorded in national surveillance statistics, yet by 2010 PT4 isolations had fallen to just 459, according to the Department for Environment, Food and Rural Affairs (DEFRA).
Control measures were introduced into the poultry industry including movement restrictions, compulsory slaughter and disinfection procedures, as well as a voluntary industry-led vaccination scheme that began in breeding flocks in 1994 and in laying flocks in 1998.
Legislation requiring compulsory slaughter of poultry infected with salmonella has now been revoked, O’Brien said, but the mass vaccination of poultry has continued by those breeders subscribing to the Lion Quality Code of Practice and using the Lion Mark on eggs.
The code of practice requires mandatory vaccination of all young hens destined to lay Lion eggs against salmonella, as well as traceability of hens, eggs and feed, a best-before date stamped on shells and hygiene controls at packing stations.
O’Brien said: "The nature of public health interventions often means that evaluating their impact is complex as they are often implemented simultaneously.
“The decrease in laboratory confirmed human cases coincides quite closely with the introduction of vaccination programmes in breeder and laying flocks,” she added.
“It is probable that no single measure contributed to the decline in salmonella cases but the relationship between vaccination programmes and the reduction in human disease is compelling and suggests these programmes have made a major contribution to improving public health."
However, O’Brien warned that there was no room for complacence with new salmonella problems emerging during the 2000s.
“…history teaches us that something else may come along to take its place.
“Robust surveillance, incorporating state-of-the-art microbiological, epidemiological, and biostatistical methods, and maintaining a prompt and comprehensive response to outbreaks is just as important now as it ever was.”
Source: Clinical Infectious Diseases
Published online ahead of print, doi:10.1093/cid/cis967
“The “Decline and Fall” of Nontyphoidal Salmonella in the United Kingdom”
Author: Sarah J. O’Brien