Zoonotic infections infections in livestock and the risk to public health - Abstract

The PHLS Case-Control Study of Escherichia coli O157 Infection in England

G K Adak*

Background

In recent years Vero cytotoxin producing Escherichia coli O157 (VTEC O157) has emerged as a pathogen of increasing world-wide importance. There is a sharply rising trend in both the number of cases of VTEC O157 infection confirmed by LEP and the number of outbreaks reported to CDSC. PHLS data show that 87% of laboratory confirmed cases are either sporadic or involved in family outbreaks. A study was conducted in order to investigate the epidemiology of VTEC O157 infection in England.

Aims and Objectives

The aim of the study was to identify and estimate the relative importance of risk factors for the acquisition of infection with VTEC O157. The objectives were:

To identify risk factors associated with VTEC O157 infection
To identify factors which make implicated food vehicles more likely to cause infection
To investigate the rôle of person to person spread in the household

Study Design

The study was an unmatched case-control study with GP nominated controls. Cases belonging to the following categories were excluded:

Cases who had travelled outside the UK in the five days before the onset of their symptoms
Cases who normally reside outside England
Cases known to be involved in general outbreaks of E. coli O157 infection
Cases known to be excreting additional gastrointestinal pathogens
Cases who had died were excluded because reliable data could not be obtained

Main Findings

Data from 369 eligible cases and 511 controls were analysed. The results show that VTEC O157 infection is associated with severe morbidity in all age groups. Approximately 40% of cases were admitted to hospital. Approximately 40% of confirmed cases did not present with bloody diarrhoea. Infection was most common among infants. Eighty one secondary cases were identified. These cases were excluded from further analyses. The most striking specific risk factors identified were: visits to farms (OR 2.45, 95%CI 1.49-4.02, p-value 0.0004); travel within the UK (OR 2.23, 95%CI 1.35-3.71, p-value 0.0019); paddling (OR 2.13, 95%CI 1.04-4.35, p-value 0.0365).

All of the risk factors identified are biologically plausible and re-inforce previous findings. Thus the prevention of VTEC O157 infection demands the development of a range of strategies designed to tackle a variety risk factors.

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