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The PHLS Farm Cohort: A Resource for Research on Zoonotic Illness Background Zoonoses are infectious diseases naturally transmissible between vertebrate animals and humans. Farmers, farm workers and their families have closer and more varied contact with a wider variety of animals than almost any other occupational group. It has been suggested that this puts them at risk of over 40 zoonoses.  Laboratories in the UK report cases of zoonotic illness to the Health Protection Agency, however reporting is voluntary, and laboratory confirmed zoonoses probably account only for a fraction of those occurring in the community. Therefore it is only possible to measure the true extent of exposure to zoonotic organisms in UK agricultural communities by carrying out community-based studies. In the past, seroprevalence studies have been performed for zoonoses, but these have usually been carried out retrospectively on clinical specimens collected for other purposes, with little epidemiological information available. Systematic data on occupational animal contact have not been provided, and information relating to the health of the human or animal populations concerned is rarely presented. It has therefore not been possible from these studies to identify on-farm risk factors for acquiring zoonoses. In order to provide an evidence base for advice on occupational and public health measures to reduce the incidence of zoonotic infection a representative, population-based sample was recruited in 1991, now named the PHLS Farm Cohort. What is the PHLS Farm Cohort? At the time of recruitment the PHLS Farm Cohort was a representative cohort of farmers, farm workers and family members from 3 regions of the UK. Recruitment was carried out in 1991 in 5 English local government districts in the catchment areas of Hereford and Preston Public Health Laboratories and in 1995 in 3 local government districts in the catchment area of Norwich PHL. MAFF lists of agricultural holdings were used as a sampling frame. The age and sex distribution of the 606 subjects recruited was representative of those employed in agriculture and living in the same local government districts. Once recruited subjects were characterised in terms of exposure to domestic and wild animals (see: Table 1) using administered questionnaire and blood samples have been taken annually to test for markers of infection. There are currently 410 participants enrolled in the cohort (68% of those originally recruited). Table 1: PHLS Farm Cohort characterised by farm type
Previous studies Since 1991 four major studies have been carried out using the PHLS Farm Cohort. Deatils of these are given in Table 2 which can be viewed by following the link: PHLS Farm Cohort: Table 2 (opens in new window). The first of these studies was a HSE-funded seroepidemiological study to identify rates of exposure and risk factors for a number of occupational zoonoses, for example: leptospirosis, lyme disease, brucellosis. Results of this study are given in Table 3 which can be viewed by following the link: PHLS Farm Cohort: Table 3 (opens in new window). The second study, funded by Department of Health, measured the prevalence of, and identify risk factors for, faecal carriage of VTEC and the presence of E. coli O157 antibodies in farmworkers. In a third HSE-funded study the cohort was screened for evidence of exposure to Borna disease virus using an ELISA developed at Health & Safety Laboratory, Sheffield and the clinical implications of the findings were assessed by lap-top administered mental health questionnaire developed at University of Wales College of Medicine. A study funded by MAFF to investigate the epidemiology of Mycobacterium bovis has recently been completed. Outputs Outputs during the 13 years since the PHLS Farm Cohort was recruited have been:
The continued care and maintenance of the cohort The PHLS Farm Cohort, with it's banked sera linked to personal exposure data, is a resource to all UK agencies with an interest in zoonoses, amongst others: HPA, NPHS, SCIEH, DEFRA, HSE. This resource was, until 2003, managed under the auspices of the Public Health Laboratory Service. Since re-organisation of health protection services in the UK there is no clear locus of responsibility for ‘care and maintainance of the cohort’, including the safe keeping of all data and samples collected from previous projects. As an interim measure a multi-agency steering group has been set up to guide and advise on the cohort's use by project teams. The membership and terms of reference of this group are available from the link: PHLS Farm Cohort: Steering Group Members and Terms of Reference (opens in new window). It is proposed that the ongoing ‘care and maintainance’ of the cohort be contracted to one agency. The agency best equipped to take on this role will be decided by the existing steering group who will also bid for funding to cover the costs required to fulfil this lead project management function. Guidance for researchers Sera and questionnaire data from the PHLS Farm Cohort are a resource available for those wishing to investigate the epidemiology of zoonotic illness. This resource is owned and managed by the PHLS Farm Cohort Steering Group, a multi-agency expert group chaired by Dr Roland Salmon of the National Public Health Service (NPHS), Wales. Terms of reference for this group are published and can be downloaded using the link: PHLS Farm Cohort: Steering Group Members and Terms of Reference (opens in new window). As sera from the cohort is a limited resource, requests for its use are subject to review by the PHLS Farm Cohort Steering Group and release of sera cannot therefore be guaranteed. Guidelines have been written in order to assist researchers wishing to gain access to sera or data from the cohort and these can be downloaded from the link: Some guidance for researchers wishing to use sera and/or epidemiological data from the PHLS Farm Cohort Publications
Last updated: 02/01/2008 |
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