LIVERPOOL, United Kingdom – Vaccination protocols introduced in the 1990s have paid off in dramatic declines in salmonella infections in the United Kingdom, according to researchers at the Univ. of Liverpool’s ’s Institute of Infection and Global Health. The research is published in Clinical Infectious Diseases.

Two studies conducted 10 years apart found that the number of salmonella cases fell from 1.6 cases per 1,000 persons from 1993 to 1996 to 0.2 cases per 1,000 persons from 2008 to 2009. Additionally, lab-confirmed cases of salmonella infections dropped to 459 in 2010 from 18,000 in 1993, according to Sarah O’Brien, a professor of epidemiology and zoonoses at the institute.

“The nature of public health interventions often means that evaluating their impact is complex as they are often implemented simultaneously,” O’Brien said. “The decrease in laboratory confirmed human cases coincides quite closely with the introduction of vaccination programs in breeder and laying flocks.

“It is probable that no single measure contributed to the decline in Salmonella cases but the relationship between vaccination programs and the reduction in human disease is compelling and suggests these programs have made a major contribution to improving public health,” she added.

An epidemic of Salmonella Enteritidis drove a 170 percent increase in infections in the UK between 1981 and 1991. Control measures were introduced, including compulsory slaughter of infected birds, disinfection procedures and voluntary vaccinations in breeding flocks (which began in 1994) and laying flocks in 1998.

The UK has discontinued mandatory slaughter of infected birds, but breeders have continued participating in the Lion Quality Code of Practice, which requires mandatory vaccination of all young laying hens as well as traceability of hens, eggs and feed. A best-before date must be stamped on shells and packing stations must have hygiene controls. Lion Mark eggs account for 85 percent of the total egg market, according to the institute.