Table 3.

Estimated coefficients of the fitted logistic regression model for seropositivity,^a before and after backward elimination

Characteristics	Saturated model		Final model
	OR (95% CI)	p-value	OR (95% CI)	p-value
Age 18–29 vs. 45–59 yearsb	1.64 (1.10–2.44)	.015	1.67 (1.13–2.46)	.0094
Age 30–44 vs. 45–59 yearsb	1.15 (0.78–1.70)	.48	1.17 (0.80–1.71)	.41
Age ≥60 vs. 45–59 yearsb	2.13 (1.46–3.12)	<.0001	1.97 (1.39–2.80)	.0002
Male vs. female	1.29 (1.00–1.67)	.050	1.30 (1.01–1.68)	.041
Vaccination yes vs. no	1.46 (0.92–2.29)	.11	–	–
Vaccination unknown vs. no	1.36 (0.90–2.05)	.15	–	–
Pertussis yes vs. no	0.99 (0.54–1.81)	.97	–	–
Pertussis unknown vs. no	0.99 (0.72–1.37)	.96	–	–
Medicationc yes vs. no	1.04 (0.71–1.54)	.83	–	–
Medicationc unknown vs. no	1.44 (0.62–3.33)	.39	–	–
Hospitalizationd yes vs. no	3.01 (0.79–11.55)	.11	–	–
Hospitalizationd unknown vs. no	1.03 (0.11–10.21)	.98	–	–
Current vs. never smoker	1.36 (0.99–1.87)	.055	1.38 (1.01–1.89)	.045
Former vs. never smoker	1.44 (1.07–1.95)	.018	1.46 (1.08–1.97)	.014

Abbreviations: CI confidence interval, OD optical density, OR odds ratio, vs. versus

^a>0.3 OD units

^bThe age group with the lowest seropositivity was used as the reference

^cAny antibiotics and/or other medication (i.e., any cough medicines) for lower respiratory tract infections or (suspected) pertussis infections in the previous 12 months

^dHospitalized due to respiratory infections in the previous 12 months