Poultry Meat and Human Salmonellosis: Establishing the Epidemiological Relationship

Oboegbulem, Stephen Ike (1990) Poultry Meat and Human Salmonellosis: Establishing the Epidemiological Relationship. PhD thesis, University of Glasgow.

Abstract

Extensive literature review confirms that in the industrialized countries, salmonellosis is a major public health problem, causing considerable social and economic losses. Non-typhoid salmonellosis occurs primarily as a foodborne zoonosis. There are different animal sources of human infections, and this raises the question of determining and defining which meat types constitute the major hazards for man. The studies reported in this thesis were designed to establish and clarify any epidemiological relationship between consumption of poultry meat and human salmonellosis. Three epidemiological approaches were employed: A 20-year retrospective study was undertaken to determine the epidemiological characteristics of foodborne salmonella infections and outbreaks. It was hoped that the retrospective analysis would generate some hypotheses on the incidence, risk factors, and trends of human salmonellosis in Scotland. All the 1,791 outbreaks of foodborne infections and intoxications recorded by the Communicable Diseases (Scotland) Unit (CD(S)U) between 1980 and 1987 were computer-analysed. A one in 5 systematic sample (n = 5,776) of approximately 29,000 human salmonella infections (laboratory reported isolations) listed in the Weekly and Annual Reports of the CD(S)U for the period 1968 to 1987 was also computer-analysed. Eight-five per cent of all foodborne outbreaks recorded from 1980 to 1987 were caused by the salmonellae. Salmonella food poisoning has been increasing in Scotland, as in England and Wales. Laboratory isolations of salmonellae were made from an average of 1,400 persons per year, and the standardized crude incidence rate is approximately 30/100,000 per year. Both the crude incidence and the standardized incidence rate showed a trend of a steady rise. There was a three-fold (30096) increase in the standardized incidence rate from 14/100,000 population per year for the period 1968-72 to 42/100,000 per year during 1983-87. With a mean age-specific incidence rate of 63/100,000 per year, children 5 years old and below are at highest risk of foodborne salmonellosis. Although highest case fatality rate occurs among the elderly, the age-specific incidence rate among persons over 70 years old is comparatively very low (15. 3/100,000 per year). Significantly higher incidence rates of salmonella infections were recorded in males than in females. There is a consistent seasonal trend in salmonella infections and outbreaks; more than half of all the outbreaks occurred during the months of July, August and September. S. typhimurium, S. enteritidis and S. virchow are the three major causes of foodborne salmonella infections and outbreaks. Up to 1985, S. typhimurium remained the primary cause of salmonellosis; but since 1986, S. enteritidis has assumed the primary place. Between 1968 and 1987, there was a four-fold (400 per cent) increase in the incidence of S. enteritidis; the upsurge in S. enteritidis seems to be due to an unprecedented increase in the incidence of phage type 4 in poultry products. Poultry meat was the primary vehicle of foodborne salmonella outbreaks, accounting for 69 per cent of all meatborne episodes. Between 1975 and 1987, there has been 400 per cent increase in the proportions of outbreaks in which poultry was implicated; and there has been no change in the primary place of poultry during the past 10 years. From the retrospective analysis, the hypothesis is that poultry is the major risk factor; consumption of poultry meat is significantly associated with salmonella infections. In most reported incidents of salmonellosis, the evidence which incriminates poultry meat is only circumstantial. In many outbreaks, the causative salmonella types are isolated from both clinically infected and symptomless excretors. It seems important to be able to demonstrate an epidemiological association between consumption of poultry meat and salmonella excretion without relying on investigation of clinical incidents. Poultry meat used in a catering establishment can be screened to identify salmonella types to which the consumers are exposed. Salmonella excretion (an indicator of salmonella infection or transient carriage) in the consuming population can be investigated by parallel monitoring of the sewers draining the defined population area. By comparing the salmonella types isolated from the poultry meat and the sewers, and the frequency of isolation of identical types, an epidemiological association between the poultry meat and human infection can be assessed. This was the overall objective of the second epidemiological approach employed - the bacteriological surveys. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Epidemiology, Public health
• Date of Award: 1990
• Depositing User: Enlighten Team
• Unique ID: glathesis:1990-78066
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Feb 2020 12:09
• Last Modified: 28 Feb 2020 12:09
• URI: https://theses.gla.ac.uk/id/eprint/78066