Nine cases of measles have been reported and confirmed since the beginning of September on the East Rand, the Gauteng department of health reported on Friday.
It said the Boksburg and Benoni health sub-districts had a total of five and four laboratory cases each.
"An investigation into the disease proved a linkage with approximately 30 clinical measles cases, which can be traced to nursery schools and primary schools in these areas," the department said.
"Not only children, but also adults are being infected. The movement of people across municipal borders makes the containment and prevention of the viral disease particularly difficult."
The department said multi-professional rapid response teams on the East Rand have been put on alert to carry out containment and control measures to prevent the further spread of the disease.
The department appealed to all parents in Gauteng to ensure that their childrens' immunisation against measles was up to date. - Sapa