Study of infectious intestinal disease in England: rates in the community, presenting to general practice, and reported to national surveillanceBMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7190.1046 (Published 17 April 1999) Cite this as: BMJ 1999;318:1046
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Study of infectious intestinal disease in England underestimates morbidity due to specific pathogens
EDITOR - The paper by Wheeler et al is a very valuable estimate of
the burden of symptomatic infectious intestinal disease in the UK.1 One
aspect of their findings was the high proportion (55%) of community
episodes where no pathogen was identified. It is suggested that this study
severely underestimates the prevalence of certain intestinal pathogens.
For example, the authors calculate the incidence of cryptosporidium
infection in the community study to be only 0.81 (95% CI 0.26-2.5) per
1000 person years.
Another approach to determining the incidence of an infectious
disease is to determine the prevalence of antibodies in the community and
then calculate the annual attack rate required to give that degree of
antibody positivity. Assuming that an individual remains antibody positive
for life after an infection, then this attack rate is given by the simple
cases/100 person years = % seropositive / average life expectancy
There have been very few studies of anti-cryptosporidial antibodies
in the UK. However, McLauchlin et al. reported of 21% and 49% in two
areas.2 In Oklahoma, US rates in adolescents up to 58%.3 Given that the
life expectancy in the UK is about 76 years, this would give an estimated
attack rate of up to 6.58/1000 person years (for 50% positivity), some 8
times more frequent then suggested by Wheeler et al. This figure itself is
probably a gross underestimate given the observation that infection in
human volunteers offers little protection against reinfection one year
later.4 If individuals suffer repeated infection or if antibody levels
become undetectable after only a few years, the real infection rate may be
many times greater still.
The arguments presented here equally well apply to other pathogens
such as SRSV and Rotavirus. We must be cautious about using data collected
from this type of study in assessing the health and cost benefits of
public health interventions aimed at single pathogens. There is a need for
more effort to be directed at study of the sero-epidemiology of various
1. Wheeler JG, Sethi D, Cowden JM, Wall PG, Rodrigues LC, Tomkins DS,
et al. Study of infectious intestinal disease in England: rates in the
community, presenting to general practice, and reporting to national
surveillance. BMJ 1999; 318: 1046-50.
2. McLauchlin J, Casemore DP, Moran S, Patel S. The epidemiology of
cryptosporidiosis: application of experimental sub-typing and antibody
detection systems to the investigation of water-borne outbreaks. Folia
Parasitol 1998; 45: 83-92.
3. Kuhls T, Moiser DA, Crawford D, Griffs J. Seroprevalence of
cryptosporidial antibodies during infancy, childhood and adolescence. Clin
Infect Dis 1994; 5: 731-5.
4. Okhuysen PC, Chappell CL, Sterling CR, Jakubowski W, DuPont HL.
Susceptibility and serologic response to healthy adults to reinfection
with Cryptosporidium parvum. Infect Immun 1988; 66: 441-443.
Competing interests: No competing interests