Table 2.

Multivariable associations between participant demographic and clinical characteristics and symptom severity (N = 2,374) ¹

Characteristic	Difference in average adjusted symptom severity score 2	Standard error	P-value
Age (years) (ref.: 18–49)
50-64	−0.19	0.35	0.51
≥ 65	−3.08	0.49	< 0.0001
Female gender	0.99	0.18	< 0.0001
Days elapsed between symptom onset and enrollment date (ref.: ≥ 7)
5-6	0.06	0.28	0.82
3-4	0.04	0.26	0.87
1-2	−0.27	0.27	0.31
0	−2.45	0.53	< 0.0001
Number of ambulatory care visits in the past five years	0.01	0.001	< 0.0001
Influenza infection 3	1.73	0.36	< 0.0001
Vaccinated against influenza	−0.39	0.24	0.11
Total cholesterol (mg/dL) (ref.: < 200)
200-239	0.67	0.19	0.0006
≥ 240	0.46	0.32	0.15
Body mass index (kg/m2) (ref.: < 25)
25-29	0.27	0.24	0.27
≥ 30	0.61	0.22	0.005
Smoking (ref.: Never)
Current	0.63	0.23	0.006
Former	0.73	0.19	< 0.0001
Interaction: Age x influenza
50-64 × influenza infection	0.23	0.72	0.75
≥ 65 × influenza infection	4.21	1.37	0.002
Interaction: Age × influenza vaccination
50-64 × vaccinated	−0.48	0.41	0.24
≥ 65 × vaccinated	1.45	0.57	0.01
Interaction: Influenza infection x influenza vaccination	0.92	0.68	0.17
Interaction: Age x influenza infection x influenza vaccination
50-64 x influenza infection × vaccinated	−1.02	1.11	0.36
≥ 65 × influenza infection×vaccinated	−6.75	1.68	< 0.0001

¹Bolded values denote point estimate was significant (p < 0.05). Significant exposures in the crude models were also considered for inclusion in the final reduced model.

²Values are reported as point estimate ± standard error, p-value. Positive values with p < 0.05 indicate a significantly greater symptom severity score relative to the reference category (or 1-unit increase for continuous predictors) and negative values with p < 0.05 indicate a significantly lower symptom severity score relative to the reference category.

³Influenza infection refers to infection with either influenza A or B.