Early exposure to secondhand tobacco smoke and the development of allergic diseases in 4 year old children in Malmö, Sweden

Table 2 Odds ratios (OR) and 95% confidence intervals (CI) of having an allergy or having sought medical care due to allergic symptoms during the last year in 4-year old children in Malmö, Sweden, by presence of secondhand tobacco smoke and presence of parental allergy

	Allergy†	Having sought medical care† due to allergic symptoms
	Adjusted model‡ OR; 95% CI*	Adjusted model‡ OR; 95% CI*
Secondhand tobacco smoke
Secondhand tobacco smoke during the first month of age (yes vs. no)*	1.20 (0.83, 1.73)	1.17 (0.81, 1.69)
Secondhand tobacco smoke during eight month of age (yes vs. no)	1.12 (0.77, 1.64)	1.39 (0.97, 1.99)
Parents with an allergy
At least one parent with an allergy (yes vs. no)	4.79 (3.51, 6.71)	2.46 (1.81, 3.34)
Mother having an allergy (yes vs. no)	4.85 (3.58, 6.56)	2.57 (1.89, 3.49)
Father having an allergy (yes vs. no)	3.51 (2.61, 5.01)	1.74 (1.25, 2.41)

* OR, odds ratio; CI, confience interval; Secondhand tobacco smoke was categorized into no (no secondhand tobacco smoke at all) and yes (daily secondhand tobacco smoke, including smoking outside).
† Parents reporting that the child had or had had allergic diseases (i.e., atopic eczema, hay fever, asthma or food allergies). Those reporting confirmed allergies (tested positive in skin prick test, in blood test and by provocation) or having severe allergies were considered as having an allergy;. Allergies were further assessed by the question if the child had sought medical care during the last 12 months, due to atopic eczema, food allergies or asthma.
‡ Adjusted for sex, year, maternal smoking during pregnancy, maternal educational level, parents'country of birth, taken part of parental education program, crowded living and having a pet.

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