Follow-up of sporadic cases of food-borne infection: comparison of a postal questionnaire with a personal visit

The aim of the study was to evaluate the follow-up of sporadic cases of sus pected food-borne illness by either a postal questionnaire or a personal vi sit by environmental health staff. This was achieved by comparing the pract ice in two authority areas within the West Pennine Health Authority in the north west of England. We included all identified cases of suspected food p oisoning, campylobacteriosis, cryptosporidiosis, salmonellosis and dysenter y occurring in the district between 1 July and 30 September 1996. The main outcome measures were: (1) the proportion of all cases which were successfu lly followed-up by each method; (2) the timeliness of follow-ups; (3) quali tative estimation by environmental health staff of the data obtained. Visit ing by environmental health staff was successful in obtaining information f rom 76.3% (106/133) of cases, while the postal questionnaires elicited a 52 % (50/96) response rate. We found that 70.5% of visits occurred within one week of notification. Although 69.8% (67/96) of questionnaires were issued within one week of notification, only 16% of replies to the questionnaire w ere received within this period. The information provided on the returned q uestionnaires was found by environmental health staff to be generally as us eful as that obtained by visiting.