The Figure shows the date of diarrhoea onset for notified cases of Cryptosporidium infection whose postcode of usual residence was indicated as being in one metropolitan region of Melbourne. The onset for the first case was on 17 February with sporadic one or two cases cases, then no cases until a second peak of five cases on 7 March. A second cluster of one or two cases was evident between 10 and 12 March. The final two cases had an onset on 18 and 21 March respectively.