Medical experts traced all known Hampshire contacts of three-year-old Isla Johnston – Britain’s first victim in seven years of the killer diphtheria virus.
Tests were carried out in Swansea in an attempt to find the carrier of the disease.
A spokesman for the Wessex Regional Health Authority said that fewer than 20 of the contacts had come from Hampshire.
Isla, from London, died shortly after being admitted to the Royal Hampshire County Hospital, Winchester.
She was staying with friends at Horton Heath, near Eastleigh, when she became ill. She was not inoculated against diphtheria.
Health officials feared that children were not being vaccinated because parents were afraid of side effects.