Parents are being alerted to the symptoms of scarlet fever following a dramatic rise in the area.
Public Health England said the number of cases in Hertfordshire and the surrounding area has risen from 127 last year to 214 this year.
The warning follows a nationwide increase, which has seen the highest levels of the illness since 1990.
- Sore throat
Dr Theresa Lamagni, Public Health England’s head of streptococcal infection surveillance, said: "Between 12 to 48 hours after this, a characteristic rash develops. Cases are more common in children although adults can also develop scarlet fever. Symptoms usually clear up after a week and the majority of cases can be treated with a course of antibiotics to reduce risk of complications.
"PHE recommends that people with symptoms of scarlet fever see their GP. Once children or adults are diagnosed with scarlet fever we strongly advise them to stay at home until at least 24 hours after the start of antibiotic treatment to avoid passing on the infection."
Scarlet fever is an infectious disease caused by group A streptococcus bacterium. Typically there is a seasonal rise December and April each year.