Five laboratories serving a population of 1·5 million participated in a 2-year survey of campylobacter, salmonella and shigella infections in patients suffering from gastrointestinal symptoms. In total, 33857 faecal specimens were examined of which 5·5% yielded campylobacters, 3·4% salmonellas and 0·8% shigellas; incidence of infection (per 100,000 population per year) was 58, 38 and 9 respectively. Peak incidences occurred at different ages for each organism: campylobacter, 1–4 years (183); salmonella, less than 1 year (181); shigella, 1–4 years (17). There was a secondary peak in campylobacter incidence in patients aged 15–24 years (87), which was not seen with salmonella or shigella infections.
By recording the age and sex of all patients submitting faecal specimens, it was shown that sampling rates were disproportionately high in infants aged less than 1 year (12:1 relative to other ages). Thus the percentage of faecal samples positive in infants – in sharp contrast to incidence values – was the lowest of any age group for all three organisms. By taking the numbers of faecal specimens tested as denominators in this way, the highest campylobacter isolation rates were in young adults, with a notable male predominance in the 15–24 year (1·7:1) and 45–54 year (1·6:1) age groups. This male predominance was accentuated during the summer (2·1:1) when incidence was generally high. The maximum percentage isolation recorded by any laboratory was 32·5% in males aged 15–24 years in June.
The reasons for this pattern of campylobacter infection are unknown, but the similarity of the results between laboratories and the regularity of the seasonal fluctuations recorded over the last G years indicate that the sources and routes of infection are geographically similar and stable, yet different from those of salmonellosis.