Population-Based Sentinel Surveillance as a Means of Elucidating the Epidemiology of Campylobacter Infection
The public health significance of campylobacters lies in their role as enteropathogens of man. Zoonotic in origin, they are the most commonly reported bacterial cause of gastrointestinal infection in the developed world. Approximately 46,000 laboratory-confirmed cases are reported annually in England and Wales, and this figure underestimates community disease by a factor of eight. Infection is unpleasant and, whilst self-limiting, a tenth of cases require hospital admission for their illness. Sequelae such Irritable Bowel Syndrome, Reactive Arthritis and Guillain-Barré Syndrome compound the problem. Despite the significant public health burden posed by campylobacters, our understanding of the epidemiology of Campylobacter infection is limited. This deficiency relates to a combination of the natural history of the microorganism, the high disease incidence which exists and the epidemiological tools applied thus far to its study. In order to gain a better understanding of the epidemiology of Campylobacter infection the Campylobacter Sentinel Surveillance Scheme was conceived in 1998 and established in 1999. Through the integration of standardised epidemiological and microbiological data, it aimed to generate systematically new hypotheses for potential vehicles of infections, or transmission pathways, for campylobacteriosis. Twenty-two health authorities, representing all NHS regions at that time in England and in Wales and with a population of over 12 million people, participated in the study, which ran from May 2000 until April 2003. Standardised epidemiological data were captured on over 20,000 cases over the surveillance period and these were combined with microbiological data from detailed strain characterisation of patients‟ strains, referred at the same time. Case-case comparisons and disease determinant analysis were the epidemiological tools most commonly applied to the data. The research carried out by the candidate demonstrated that age, gender, ethnicity, occupation and socioeconomic status are major determinants for Campylobacter infection in England and Wales, and that variation in behaviour throughout the week also has a bearing on risk. It has shown that campylobacteriosis cannot be considered a single disease, as exposure differences exist in cases infected with different Campylobacter species or subspecies, and these differences can be confounded by foreign travel status. The fact that disease incidence amongst foreign travellers is country-specific suggests that the above exposure differences will be confounded further by travel destination. It has shown that outbreaks of campylobacteriosis occur more commonly than described previously, suggesting that an opportunity for furthering our understanding of infection is being missed. Finally, the dose-response relationship for Campylobacter infection has been investigated, highlighting potential implications for the design of future epidemiological studies. Policy makers should be aware that future case-control studies of Campylobacter infection will need to be larger or more complex, and hence more costly. Such costs should be weighed against the opportunity for a more accurate assessment of disease risk, leading to improved evidence-based policy development. Researchers should focus on assessing rapidly and by non-invasive means, previous exposure to campylobacters amongst healthy controls, improving further the accuracy of case-control studies, which remain the epidemiological method of choice for studying this disease. This study has demonstrated that the systematic collection of standardised epidemiological information on all cases of Campylobacter infection, reported from large, well defined populations over a prolonged period, coupled with detailed strain characterisation, can lead to public health gains.