Epidemiology and control of egg-associated Salmonella enteriditis in the United States of America

Abstract

The isolation rate for Salmonella enterica serotype Enteritidis (SE) in humans in the United States of America (USA) increased from 1,207 sporadic isolates identified in 1976 (0.6 isolates/100,000 population) to 10,201 identified in 1995 (4.0/100,000 population). The proportion of reported Salmonella isolates which were SE increased from 5% to 25% during the same time period. In 1990,1994, and 1995, SE was the most commonly reported Salmonella serotype in the USA. Much of this increase has been associated with the consumption of contaminated shell eggs. An examination of the results of a United States Department of Agriculture (USDA) survey of spent hens at slaughter and unpasteurised liquid egg at breaker plants (liquid egg processors) in 1991 and 1995 reveals an increase in the prevalence of SE isolates overall and in most regions of the USA. SE phage type 4 (pt 4), the predominant SE phage type in other parts of the world, has emerged in the egg industry in the western USA concurrent with a sharp increase in the number of sporadic human SE pt 4 isolates in California and Utah. Research on the molecular structure and virulence of SE pt 4 isolates from the USA as compared with isolates from other parts of the world (human and poultry) should be a priority. A comparison of DNA from pt 4 isolates from the USA and Europe may provide information about the potential threat to public health and poultry in the USA from this phage type. Some regional success in the reduction of human illness as a result of SE control efforts is apparent. The Pennsylvania Egg Quality Assurance Program has shown progress in reducing SE infection in participating flocks. At a national level, however, neither the incidence of human illness due to SE nor the prevalence of Rev. sci. tech. Off. int. Epiz., 16 (2) 543 SE in flocks and unpasteurised liquid eggs have decreased significantly, despite the Implementation of the USDA 'trace back' regulation from 1990 to 1995, and intensified efforts to educate food handlers and to enforce safe food handling practices. More effort is needed to control SE at every stage of the egg continuum, from production through to consumption. A risk-reduction approach, with barriers to the introduction and multiplication of the pathogen throughout the farm-to-table continuum, is the most practical method for reducing human illness from SE in shell eggs at present. An effective long-term solution will require interdisciplinary efforts involving government, industry, consumers, and academics. Interventions should be developed and evaluated in compliance with the potential for reducing the risk to human health and cost-effectiveness.

Salmonella enterica serovar Enteritidis: a Mini-review of Contamination Routes and Limitations to Effective Control

“…Poultry infected with other egg contaminating serotypes, such as Salmonella enterica serovar Pullorum and Salmonella enterica serovar Gallinarum, are associated with drastic weight loss, a sharp decrease in egg production, and increased mortality 80,82 . On the other hand, there are typically no clinical signs in birds infected with S. Enteritidis 44 .…”

“…Although bacteriological screening of hen houses can help to identify flocks at risk 19,42,44 , it is equally difficult to isolate S. Enteritidis from hen houses even if the flock is producing contaminated eggs 14,19,33,41,77 . Previous reports have suggested that S. Enteritidis infection can be decreased in poultry using competitive exclusion by inoculating hatching chicks with beneficial bacterial cultures 65,70 .…”

Emergence of Salmonella epidemics: The problems related to Salmonella enterica serotyp Enteritidis and multiple antibiotic resistance in other major serotypes

“…Investigation of outbreaks and sporadic cases has repeatedly indicated that, when a food vehicle is identified, the most common sources of S. Enteritidis infection are poultry and poultry derivatives, particularly, in the case of outbreaks, undercooked and raw eggs [35,41,65,74]. Although contamination of egg products with other Salmonella serotypes is a long-standing problem, that has been attributed either to the use of damaged eggs or to contamination at or after breaking, the situation with S. Enteritidis is different.…”

A longitudinal study of environmental salmonella contamination in caged and free-range layer flocks

“…Undercooked and raw eggs have been heavily implicated in human infection with S. Enteritidis (Coyle et al ., 1988;St Louis et al ., 1988;Hogue et al ., 1997;Palmer et al ., 2000;Centers for Disease Control and Prevention, 2004;De Buck et al ., 2004;Crespo et al ., 2005). This serotype is able to cause long-term colonization of the chicken reproductive tract and become deposited within egg contents (Berchieri et al ., 2001;Okamura et al ., 2001;Amy et al ., 2004;Guard-Bouldin et al ., 2004), and in addition will cause external contamination of the shell (Messens et al ., 2005).…”