Associations of hand-washing frequency with incidence of acute respiratory tract infection and influenza-like illness in adults: a population-based study in Sweden

Table 3 Relative risks (rate ratios with 95% confidence intervals) for self-reported influenza-like illness (ILI) stratified by household size and acute respiratory tract infection (ARI) stratified by health care work, both by different hand-washing frequency

Subset and strata		Typical hand-washing frequency
Subset and strata	n	2-4 times daily	5-9 times daily	10-19 times daily	≥20 times daily	Interaction p-value
Among all responding participants, outcome = ILI		Rate ratio (95% confidence interval)
Household size 1 person¹	639	1 (reference)	0.69 (0.33-1.45)	1.89 (0.91-3.91)	1.04 (0.45-2.38)	0.09
Household size 2 persons¹	1137	1 (reference)	1.16 (0.62-2.19)	1.27 (0.66-2.46)	1.25 (0.63-2.50)
Household size ≥3 persons¹	706	1 (reference)	1.03 (0.52-2.04)	0.88 (0.43-1.82)	0.89 (0.41-1.93)
Among gainfully employed participants, outcome = ARI
Non-health care work²	1104	1 (reference)	1.20 (0.85-1.69)	1.39 (0.97-2.00)	1.19 (0.80-1.76)	0.13
Health care work²	170	1 (reference)	0.31 (0.11-0.90)	0.49 (0.18-1.31)	0.45 (0.18-1.13)	0.13

¹adjusted for age, gender, educational level, vaccination status, child- and overall contact, household size.
²adjusted for age, gender, educational level, vaccination status, household size, physical-, child-, and long contacts, and health care work status.

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