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Table 3 Relative risks of history of DTaP vaccination for pertussis according to case definition

From: Pertussis outbreak in university students and evaluation of acellular pertussis vaccine effectiveness in Japan

Definition of pertussis Number Case Attack rate (%) Relative risk (95% CI) Relative riska (95% CI)
Probable cases        
Less than 4 doses or no doses 23 7 30.4 1   1  
4 doses 225 31 13.8 0.45 (0.23-0.91) 0.48 (0.24-0.97)
Probable + Suspected cases        
Less than 4 doses or no doses 23 15 65.2 1   1  
4 doses 225 100 44.4 0.68 (0.49-0.95) 0.70 (0.51-0.98)
Anti- PT antibody titers after outbreak ≥ 100EU/mL        
Less than 4 doses or no doses 23 2 8.7 1   1  
4 doses 225 13 5.8 0.64 (0.16-2.76) 0.64 (0.16-252)
Diagnosed as pertusis at medical institutions        
Less than 4 doses or no doses 23 2 8.7 1   1  
4 doses 225 17 7.6 0.87 (0.21-3.53) 0.74 (0.21-2.61)
  1. DTaP: diptheria, tetanus, and pertussis; CI: confidence interval; PT: pertussis toxin.
  2. Clinical criteria: (1) cough illness lasting  2 weeks; (2) paroxysms of coughing; (3) inspiratory “whoop”; (4) post-tussive vomiting.
  3. Probable case: a patient who met cough illness lasting  2 weeks with at least 1 item in the other clinical criteria.
  4. Suspected case: a patient who met at least 1 item in the above 4 clinical criteria.
  5. aAdjusted by department using the Mantel-Haenszel method.