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How long should patients with Salmonella typhi or Salmonella paratyphi be followed-up? A comparison of published guidelines.

Records were examined for 242 individuals infected with Salmonella typhi or S. paratyphi identified in Birmingham between 1981 and 1988, with a total of 335 person years of follow-up. Of these cases 77 and 78 per cent respectively were followed beyond the point at which surveillance would have ceased under guidelines published by the American Public Health Association and by the Public Health Laboratory Service for England and Wales. Under these two sets of guidelines only seven (3.8 per cent) and eight (4.3 per cent) cases respectively had subsequent positive faecal or urine cultures over a median of 335 and 295 days of additional follow-up. After 0, 1, 2, 3, 4 and 5 prior consecutive negative sets of cultures obtained at weekly intervals the likelihood of the next set of cultures being positive was 26, 9, 5, 2.2, 2.4 and 0 per cent respectively. Only 38 (1.7 per cent) of 2184 follow-up urine cultures were positive; these results did not influence duration of follow-up. Only 26 (2.6 per cent) of 1002 contacts were infected; the yields of the first, second and third sets of cultures were 1.5, 0.6 and 0.5 per cent respectively.