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

BMC Infectious Diseases

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

Definition of pertussis	Number	Case	Attack rate (%)	Relative risk	(95% CI)	Relative risk^a	(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)

DTaP: diptheria, tetanus, and pertussis; CI: confidence interval; PT: pertussis toxin.
Clinical criteria: (1) cough illness lasting ≧ 2 weeks; (2) paroxysms of coughing; (3) inspiratory “whoop”; (4) post-tussive vomiting.
Probable case: a patient who met cough illness lasting ≧ 2 weeks with at least 1 item in the other clinical criteria.
Suspected case: a patient who met at least 1 item in the above 4 clinical criteria.
^aAdjusted by department using the Mantel-Haenszel method.

ISSN: 1471-2334