Pertussis cases rise 10-fold among older children and adults in England and Wales

Pertussis is affecting nearly 10 times the number of older children and adults this year than when the disease last peaked in England and Wales in 2008, figures show.

The Health Protection Agency has written to GPs in areas where the incidence is highest, advising them to look out for symptoms in children aged over 15 as well as adults and to treat them with antibiotics to stop the infection spreading to babies and vulnerable adults.

The agency is keeping the Department of Health for England up to date with the situation and is discussing what, if any, measures need to be taken to prevent further spread of the infection. The options include vaccinating adolescents and “cocooning,” where close relatives of a newborn baby are vaccinated against pertussis, both of which have been used in other countries with outbreaks.

Pertussis is a cyclical disease whose incidence peaks every three to four years. The latest outbreak started in the second half of 2011.

The number of cases of pertussis in England and Wales reached 1781 at the end of May 2012, compared with a total of 1118 cases in the whole of 2011. There have been five deaths so far this year, all of them young babies. This compares with seven deaths in the whole of 2008.

There has been a shift in who is affected since the outbreak started. In 2011 most of the cases were among children under 1 year, as expected, but now many more cases are being seen in children over 15. So far this year there have been 1324 cases in this age group, compared with 157 cases to the end of May 2008.

Gayatri Amirthalingam, consultant epidemiologist at the Health Protection Agency, told the BMJ that part of the latest rise in cases may be because of greater awareness among GPs and a new blood test for antibodies to Bordetella pertussis. However, she also said that immunity conferred by the vaccine wanes over time, which may explain the spread of cases in older children and adults.

Several other countries in Europe and the United States and Australia have also seen a rise in incidence in the past year.

In the US there have been more than 17 000 cases of pertussis and 10 deaths up to 12 July, compared with a provisional figure of 15 000 cases for the whole of 2011.1 Although infants under 3 months are most affected, incidence is rising in adolescents aged 13 and 14 years, said the US Centers for Disease Control and Prevention.

Wisconsin and Washington states have been particularly badly hit, with more than 3000 cases each to mid-July, compared with about 200 cases in the same period last year.

To help control the infection the US introduced a booster vaccine for adolescents a few years ago.

In the UK “the primary aim of the [childhood] vaccination programme is to protect babies from infection with pertussis,” said Amirthalingam. However, the evidence of the effectiveness of cocooning is weak, she said.