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Pathogen adaptation has been proposed to contribute to the resurgence of pertussis. A striking recent example is the emergence of isolates deficient in the vaccine component pertactin (Prn). This study explores the emergence of such Prn-deficient isolates in six European countries. During 2007 to 2009, 0/83 isolates from the Netherlands, 0/18 from the United Kingdom, 0/17 Finland, 0/23 Denmark, 4/99 Sweden and 5/20 from Norway of the isolates collected were Prn-deficient. In the Netherlands and Sweden, respectively 4/146 and 1/8 were observed in a later period (2010–12). The Prn-deficient isolates were genetically diverse and different mutations were found to inactivate the prn gene. These are indications that Prn-deficiency is subject to positive selective pressure. We hypothesise that the switch from whole cell to acellular pertussis vaccines has affected the balance between ‘costs and benefits’ of Prn production by Bordetella pertussis to the extent that isolates that do not produce Prn are able to expand. The absence of Prn-deficient isolates in some countries may point to ways to prevent or delay the spread of Prn-deficient strains. In order to substantiate this hypothesis, trends in the European B. pertussis population should be monitored continuously.

This study aimed to evaluate the performance of polymerase chain reaction (PCR) methods used for the diagnosis of pertussis in laboratories within Europe in 2011. National reference laboratories in 25 European countries were contacted and a total of 24 laboratories from 19 countries agreed to participate in the study. A panel of seven samples of DNA from Bordetella pertussis, Bordetella parapertussis and Bordetella holmesii plus a negative control were distributed and analysed according to the routine PCR methods in each laboratory. The study took place in 2011. Nineteen laboratories used a real-time PCR approach, four laboratories used block-based PCR and one laboratory used a combination of methods. Six different combinations of amplification targets were used, and ten laboratories tested only for the presence of B. pertussis DNA. All laboratories (24/24) correctly identified a sample with high concentration of B. pertussis DNA, while three misidentified the B. parapertussis DNA as B. pertussis and 15 misidentified the B. holmesii DNA as either B. pertussis or B. parapertussis. There was a wide variation in the methods used for PCR-based diagnosis of pertussis among the European laboratories. Several laboratories were not able to discriminate between DNA samples from different Bordetella species.