Relation between incidence of gonorrhoea in Sheffield and efficiency of contact tracing: a paradox?

An attempt has been made to correlate the yearly incidence of gonorrhoea in Sheffield (1979-85) with two variables to show contact tracing efficiency: infectious patient days (days from the start of contact tracing to the attendance of contacts) and the percentage of source contacts brought to investigation within 30 days. No such correlation has been found. The possible reasons for this, which include the unreliability of incidence figures as a sole criterion of control and the organisation of contact tracing activities, are discussed.