Clinical and epidemiological picture of B pertussis and B parapertussis infections after introduction of acellular pertussis vaccines.

Objective: To investigate the clinical picture and frequency of Bordetella pertussis and B parapertussis infections after introduction of acellular pertussis (acP) vaccines in Germany.

Methods: Prospective surveillance for B pertussis and B parapertussis in 14 144 toddlers. Pertussis vaccination coverage was 86%, either with acP (75%) or whole cell pertussis (wcP) vaccine (11%). All children presenting with cough for more than seven days were examined for B pertussis and B parapertussis by culture, PCR, and serology (for cough duration > or =21 days).

Results: There were 180 Bordetella infections; 116 (64%) were caused by B pertussis and 64 (36%) by B parapertussis. Incidence rates were 4.8 and 2.8 per 1000 person-years, respectively. Paroxysmal cough, post-tussive whooping, and vomiting > or = 21 days was found in 53%, 22%, and 8% of all B pertussis cases and in 22%, 5%, and 0% of all B parapertussis cases, respectively. A total of 81/116 (70%) B pertussis cases and 56/64 (87.5%) B parapertussis cases had received at least one dose of pertussis vaccine. Typical pertussis with paroxysmal cough > or = 21 days was present in 29/35 (83%) unvaccinated B pertussis cases, in contrast to 33/81 (41%) vaccinated B pertussis cases.

Conclusions: Following the increase of pertussis vaccination coverage, we observed a relative increase of B parapertussis cases in comparison to B pertussis cases. In vaccinated children B pertussis disease frequently presented as a mild disease, clinically difficult to distinguish from diseases associated with coughing caused by B parapertussis and other viral or bacterial infections.