A Case-Case Comparison of Campylobacter coli and Campylobacter jejuni Infection: A Tool for Generating Hypotheses

Iain A. Gillespie, Sarah J. O'Brien, Jennifer A. Frost, Goutam K. Adak, Peter Horby, Anthony V. Swan, Michael J. Painter, Keith R. Neal, and the Campylobacter Sentinel Surveillance Scheme Collaborators

Disclosures

Emerging Infectious Diseases. 2002;8(9) 

In This Article

Abstract and Introduction

Preventing campylobacteriosis depends on a thorough understanding of its epidemiology. We used case-case analysis to compare cases of Campylobacter coli infection with cases of C. jejuni infection, to generate hypotheses for infection from standardized, population-based sentinel surveillance information in England and Wales. Persons with C. coli infection were more likely to have drunk bottled water than were those with C. jejuni infection and, in general, were more likely to have eaten pâté. Important differences in exposures were identified for these two Campylobacter species. Exposures that are a risk for infection for both comparison groups might not be identified or might be underestimated by case-case analysis. Similarly, the magnitude or direction of population risk cannot be assessed accurately. Nevertheless, our findings suggest that case-control studies should be conducted at the species level.

Campylobacters are the most commonly reported bacterial cause of acute gastroenteritis in the industrialized world.[1] In the United Kingdom (UK), laboratory reports of campylobacter have increased steadily since surveillance began in 1977; in 1999, >60,000 cases were reported (incidence rate 103.7 per 100,000). However, the true population burden of campylobacter infection is thought to be much higher. For every laboratory-confirmed case reported to national surveillance in England, an additional eight cases may be unrecognized.[2] This estimate suggests that in 1999, approximately half a million people in the UK became ill with campylobacter enteritis. The cost to the nation of a case of campylobacter infection has been estimated as £314.00 (at 1994-95 prices);[3] in 1999 campylobacter infection probably cost the nation >£150 million (US$ 225 million). The clinical complications of campylobacter infection include toxic megacolon, hemolytic uremic syndrome, Reiter's syndrome, and Guillain Barré syndrome, the most common cause of acute neuromuscular paralysis in the industrialized world.[4]

Although campylobacters were recognized as important pathogens >20 years ago, their epidemiology is still poorly understood.[5,6,7,8] Eating poultry has long been a leading hypothesis for spread of campylobacter infection, but few case-control studies have identified it as a major risk factor except in a commercial context.[9,10,11] An estimated 20% to 40% of sporadic disease might result from eating chicken.[12,13] Although a variety of food vehicles and other risk factors have been reported in several case-control studies, most cases in these studies remain unexplained by the risk factors identified.[5,6,7,8,9,10,11]

A difficulty, until recently, has been the lack of routine microbiologic characterization of clinical strains,[14] which has militated against systematic study of the epidemiology of the different species and subtypes of campylobacter. Control and prevention strategies cannot be developed and implemented without proper understanding of the epidemiology of campylobacter infection. On May 1, 2000, an active, population-based sentinel surveillance scheme for campylobacter infections was initiated in England and Wales.[15] Its aim is to generate hypotheses for human campylobacter infection by using a systematic, integrated epidemiologic and microbiologic approach. Twenty-two district health authorities are collaborating in the scheme, working with their hospital microbiology and local environmental health departments (Figure 1). The sentinel system covers a population of approximately 12.5 million and captures standardized information on approximately 15% of all laboratory-confirmed campylobacter infections in England and Wales. The health authorities are broadly representative of England and Wales as a whole.

The health authorities in England and Wales participating in the sentinel surveillance scheme for Campylobacter.

We have used case-case comparisons, an adaptation of conventional case-control methods, as suggested by McCarthy and Giesecke,[16] to generate hypotheses concerning risk factors for campylobacter infection. We report results from the first year of the study and discuss the strengths and weaknesses of case-case analysis.

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