Countries are likely to count cases in at least two different ways. First is the old fashioned way of a doctor or nurse diagnosing the disease and being legally obliged to inform the relevant authority who then forwards the information to a national centre that keeps count.
Alongside this or in addition, countries may count laboratory confirmations of pertussis infection. Many countries regard the latter as the preferable data.
Some countries do not collect national statistics, only regional ones, each of which may record data differently.
Some countries have only recently started collecting data.
There is no requirement to notify in France. Instead there is a network of paediatricians and bacteriologists in hospitals who monitor the disease and report to the Pasteur Institute.
Doctors in different countries have quite variable attitudes to their statutory obligation to notify.
Some of the data above are taken from the European Centre for Disease Prevention and Control report in which all European pertussis data for each country can be seen for the latest available year of 2014.