PhD thesis - University of Hertfordshire Research Archive

Similarly those who reported an increasing daily consumption of unboiled tap
water were more likely to present with diarrhoea and vomiting. Eating salads,
cheese and fish/shellfish was reported less commonly by cases reporting
vomiting and/or bloody diarrhoea, and few associations with infecting C.
jejuni serotype were observed.
This study suggests that for Campylobacter infection, vomiting and bloody
diarrhoea share a similar aetiology, represent the more severe end of the
disease spectrum and might relate to host susceptibility and/or infective
dose. These findings have important implications for case-control studies of
laboratory-confirmed Campylobacter infection. If heavily contaminated (“high
dose”) foods lead to severe disease then it follows that „normal‟ doses will
lead to „normal‟ disease, „lower‟ doses will lead to mild symptoms that might
be dismissed as disease and the lowest doses will lead to sub-clinical
infections. Some people will not be exposed at all (figure 5, below).
Figure 5. An extension of the dose response model for Campylobacter
infection and its hypothesised effect of case and control classification in
case-control studies.
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