The Eastern Cape department of health has confirmed that an eight-month-old child is receiving treatment at Dora Nginza Hospital for whooping cough.
The child has been at the hospital since September.
The National Institute for Communicable Diseases has warned of an increase in whooping cough cases across the country.
The Eastern Cape is not a surveillance site for the disease.
Whooping cough, also known as pertussis, is a potentially fatal and highly contagious bacterial infection.
Health spokesperson Lwandile Sicwetsha said the hospital had confirmed the diagnosis of the eight-month-old from Extension 2 in Walmer township.
“The department has implemented interventions following the identification of the case,” he said.
People close to the infected child would be monitored for 10 days and samples would be taken from them to ensure that they were not infected, he said.
“The department is enhancing its health promotion and education programme on [whooping cough].”
In August, the institute said there had been an increase in cases of whooping cough in children younger than five.
This was noticed at sites where pneumonia surveillance was being undertaken and was particularly noticeable in infants younger than a year.
An initial increase was limited to the Western Cape sites, but since January 2018 a more general increase has been spotted countrywide.
Whooping cough is a vaccine-preventable disease.
Children receive their first vaccine against the illness at six weeks.