An increase in scarlet fever cases - with numbers more than doubling in Wiltshire, Avon and Gloucestershire compared to usual - is being reported by Public Health England.
Public Health England (PHE) said that there is a "continued significant increase" in the number of cases in England.
In the last week of March officials were notified of 883 new cases. This is the highest weekly total since 1982 when weekly records began, a spokeswoman said.
More than 5,000 new cases were reported in England since the season began in September 2013, compared to an average of 1,420 cases reported for the same period in the previous ten years.
The last season to have this level of scarlet fever activity was 1989/1990 when 4,042 notifications were received.
More than 250 cases have been reported in Wiltshire, Avon and Gloucestershire compared to 115 in the same period in 2012/13.
Scarlet fever is an infectious disease caused by group A streptococcus bacterium.
Typically there are seasonal rises in scarlet fever between December and April each year, and also a cycle of increases and decreases in incidence that repeats over a period of several years.
This most recent increase is likely to be part of that cycle, says Public Health England.
Routine monitoring of surveillance data identified widespread increases in scarlet fever notifications in February 2014 compared to recent years.
These continued into March, with numbers of notifications surpassing levels seen in the last peak year (2008/09).
As a result of this increase in scarlet fever, PHE is alerting health practitioners so they can be mindful when assessing patients.
Dr Theresa Lamagni, PHE’s head of streptococcal infection surveillance, said: “The first symptoms of scarlet fever often include a sore throat, headache, fever, nausea, and vomiting. 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.
Public Health England recommends that people with symptoms of scarlet fever see their GP. Once children or adults are diagnosed with scarlet fever they are strongly advised to stay at home until at least 24 hours after the start of antibiotic treatment to avoid passing on the infection.
PHE publishes guidance for schools where infections can spread easily.
Where outbreaks occur, local health protection teams are on hand to provide a rapid response, effective outbreak management and authoritative advice.
Scarlet fever is mainly a childhood disease and is most common between the ages of two and eight years.
It was once a very dangerous infection, but has now become much less serious. Antibiotic treatment should be given to minimise the risk of complications. There is currently no vaccine for scarlet fever.
PHE continue to monitor these increases and are working closely with healthcare professionals to try and halt the spread of infection.