The number of confirmed cases in Cambridgeshire rose by nearly 20 times during 2012 after a sustained outbreak which peaked in November, when 38 cases were recorded. Since then the numbers have dropped, with 14 in December and another 14 in January. However that is still more than the whole of 2011, when there were just 10 cases in total, and 13 more than the same period last year, when there was just one single case. Dr Gayatri Amirthalingam, consultant epidemiologist for immunisation at the Health Protection Agency (HPA), said: The January figures show a welcome continued decrease of whooping cough cases since October. However Dr Amirthalingam added: It is very important to note that we usually see a reduction in cases of whooping cough at this time of year so this decrease is in line with normal seasonal patterns. Whooping cough is a highly contagious lung and airway infection which can cause severe coughing fits. It affects all ages but young infants are at highest risk of severe complications and death from whooping cough, as babies do not complete vaccination against the condition until they are around four months old. It is accompanied by a characteristic whoop sound in young children but as a prolonged cough in older children and adults. Experts say last years whooping cough outbreak was the largest for 20 years. The number of cases started to rise in May, when there were 12 confirmed instances, rising to 31 in July. It dropped slightly to 23 in August but rose again to 28 in September and 33 in October, before reaching its high point of 38 in November. The reason for the outbreak is unknown but one possible theory is that the number of people no longer immune to the virus, combined with the number of people infected, has reached a point were the spread of the illness is more likely. To tackle the rise, the HPA has encouraged more pregnant women to be vaccinated against the illness. We would like to remind pregnant women how serious this infection can be in young babies and how it can in some cases cause death, Dr Amirthalingam said. The aim of vaccinating of women between 28 and 38 weeks of pregnancy is to offer babies protection against whooping cough in the first few months of life, before they receive their own vaccines.