PhD thesis - University of Hertfordshire Research Archive

proffer a description of their ethnic origin. Future studies should take such
potential shortfalls into consideration.
7.6 Patient exposure history in relation to the weekly periodicity of
Campylobacter jejuni infection.
The seasonality of Campylobacter infection in the UK is well described and is
noted for the annual sharp increase in incidence which occurs consistently in
late spring/early summer. The pattern of infection over shorter time periods
had not been investigated previously. Accordingly, the day of onset for 5606
UK-acquired cases of C. jejuni infection reported in the first two years of the
study was calculated and examined (paper 6 (Gillespie et al., 2005)).
Disease incidence was greatest on the days during or immediately following
the weekend and cases who were ill at this time (N=3438) were more likely to
have consumed Halal meats, offal, restaurant food or water from a private
supply than cases whose illness onset occurred later in the week (N=2168).
Furthermore, compared with those who had not eaten in restaurants, cases
with a „weekend illness‟ were more likely to have consumed foods from
takeaway kebab shops and Indian restaurants.
It is tempting to conclude that, given the usual incubation period for
Campylobacter infection, cases with illness onset at the weekend or soon
after would have been exposed towards the end of the previous week.
However, the incubation period for Campylobacter infection is thought to be
inversely proportional to dose, and therefore the consumption of potentially
heavily contaminated (e.g. offal or Halal meats) foods or untreated or poorly
treated water might precipitate illness soon after. To our knowledge this is
the first time that the weekly periodicity of an infection has been studied. The
findings suggest that individuals undertake activities at the weekends which
affect their risk of Campylobacter infection. Such potential daily differences in
exposure should be considered when designing case-control studies of
Campylobacter infection, as interviewing cases and controls on different days
will increase the likelihood of differential recall bias. This method could also
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