The response rate was 56.4% (6531 questionnaires sent, 3681 completed, 50.1% boys, 49.8% girls). Only 13 cases did not complete the questionnaire prior to the screen according to protocol, and leaving these cases out of the analysis did not change the results. Mean age at completion was 9 months 6 days (range 6 months 18 days to 16 months 9 days) and first CAPAS screening 9 months 24 days (range 7 months 21 days to 13 months 24 days) (see Fig. 1).
In Table 1, ORs and 95% CI are presented for each item. Question 1 and the category ‘other’ from questions 2, 3 and 4 were dropped because of inconsistent interpretation and irrelevant responses.
Table 1 Questions in the PEPPER item pool with OR and 95% CI and results found in the literature for the corresponding risk factors for OM
Four highly significant (p < 0.001) risk factors were found: ‘having severe cold symptoms’, ‘attending day care with >4 children’, ‘having siblings’ and ‘male gender’. Risk factors significant for referral with a p value of <0.01 were ‘severe nasal congestion’, ‘siblings with a history of ear/hearing problems’ and ‘father working part time’. However, when the factor ‘siblings with a history of ear/hearing problems’ (p = 0.003) was adjusted for ‘having siblings’, this item became non-significant (OR = 1.2; p = 0.44).
‘Breastfeeding for at least 3 months’ had a paradoxical 1.5 higher odds (p = 0.01), rather than being protective for referral. ‘Season of CAPAS’ being January–March or July–September had increased odds for referral with a p = 0.05. However, the CAPAS screen is no longer in use and therefore this factor will be irrelevant in the future.
Comparison with other studies
To aid comparison, the results of the reference studies investigating more than one risk factor are also summarised in Table 1 and mentioned here, leaving wider interpretation to the discussion section. There are two reports from one single study [19, 20]. One study [21] provided only ORs without statistical significance levels and another [23] is not included in the table as ORs were not given at all. Although populations can differ and some risk factors may be more specific for hearing loss rather than for OM, the large sample size makes the present study more powerful than others with fewer false-positive findings for expected trends.
Classical risk factors
Siblings
‘Having siblings’ is a risk factor, consistent with the reference studies [17–22], although our estimate is greater in magnitude. Risk probably increases with more siblings, as reported elsewhere [21], but we were unable to test this with our data.
Day care
‘Attending day care’ was a risk factor in five of the comparison studies [18, 20–22, 24], but not in ours. We did find increased odds with ‘attending day care with >4 children’ (OR = 1.9; p < 0.001) indicating that it is indeed the number of children an infant is exposed to which is relevant [4].
Gender
Boys have almost twice the odds for developing OM-related hearing loss (OR = 1.9; p < 0.001) and this agrees with one other included study [24], as well as with the general background of literature on OM. One study [22] showed a marginal trend (OR = 1.5; p = 0.055) and another [21] reported an increased risk without specifying significance. Overall, boys are at raised risk for OM [4, 24, 26].
Genetic disposition
‘Siblings with a history of ear/hearing problems’ emerged as a risk factor (OR = 1.7; p = 0.003), consistent with one previous study [22]. However, upon adjustment for ‘having siblings’ this risk decreased and was no longer significant. It seems that ‘having siblings’, an environmental risk factor, is a stronger risk factor than genetic disposition. Having ‘parents with a history of ear/hearing problems’ was not a risk either.
Parents’ working status
‘Father working part time’ had significantly higher odds (OR = 2.0; p = 0.007), while mother’s working status appeared to be unrelated to referral. There were no studies for comparison.
Breastfeeding
‘Breastfeeding’ emerged as an apparent risk rather than a protective factor. One reference study [23] reported breastfeeding as protective, while six other studies [17–22, 25] were unable to do so. One [22] did report that the longer a child was breastfed, the less the risk for developing OM. Varying definitions of breastfeeding or the absence thereof make comparison difficult (>7 months of breastfeeding [22]; exclusive breastfeeding for 6 months [25]; exclusive breastfeeding for >4 months [17, 22]; median of 2 months breastfeeding [18]; at least 6 months breastfeeding [19, 20]; no definition [23] [21, 24]).
Upper respiratory tract infection symptoms (URTI)
Mouth breathing, snoring and nasal congestion can all be symptoms of URTI and can be related to adenoid hypertrophy. These factors could therefore impose a risk for developing OM and OM-related hearing loss. Neither ‘severe mouth breathing’ nor ‘severe snoring’ appeared to be risks here or in another study [18].
‘Severe nasal congestion’ appeared as a risk here (OR = 1.8; p = 0.006), and in one reference study [25] which showed that the risk increased with growing number of days with nasal congestion. ‘Severe cold symptoms’ (OR = 1.9; p < 0.001), which is less specific, embracing coughing, common cold symptoms and sore throat, was also significant in all four studies reporting on it [18–21, 23].
The understanding of ‘severe cold symptoms’ as well as ‘severe nasal congestion’ probably varies much amongst parents and might be rather imprecise. Although we are obviously not dealing with a homogenous group, the results show that these items do predict referral and therefore they can be of interest.
Ear and hearing problems
Having had a history of hearing problems [18], ear infections [18, 21, 24, 25] or early OME [23] or early otitis [25] have all been reported as a risk for developing chronic OM. However, they were not related to hearing in our study, or in one other study [19, 20]. Our study population was very young, making it difficult for their parents to detect hearing loss or ear infections, and this could have influenced the results.
Smoking
Smoking around the child by household members or the number of cigarettes smoked inside the house did not appear to be a riks factor. This is in line with the results of several recently completed studies [18–23]. However, one of the reference studies [17] found that smoking 10–19 cigarettes per day was a risk, although smoking >20 was not. Another study [25] found that the number of smokers around the child did increase the risk of persistent OM, although in that study the number of cigarettes smoked was not a significant risk. We did not ask about smoking habits around the child outside the house, and therefore the results may be an underestimation.
Season
OM is least prevalent in summer [3, 5, 22] and OM first detected in fall and winter has a greater tendency to persist [6]. Two reference studies [17] [18] confirmed this classical effect. We did not find season to be a risk factor when considering the four traditional seasons. However, when October through March were compared to April through September, we did find a 1.5 higher odds for referral (p = 0.065), which was in concordance with two other studies [22, 24].
Less conventional risk factors
Prenatal and birth characteristics
Low birth weight was not defined uniformly, hindering comparison (<2500 g [19, 22, 25]; <3100 g [17]; <3400 g [18]). We used the less specific term ‘delay in growth’ as a marker for low birth weight. It did not appear to be a risk factor. Two reference studies [17, 18] found low birth weight to be a risk factor, two did not [22, 25], and one [19] even found low birth weight to be protective.
Prematurity is usually defined as a gestational age <37 weeks [17, 19, 20], although <38 weeks has also been used [22]. One study [18] analysed prematurity appropriately as a continuous measure, finding all children born before a gestational age of 40 weeks having an increased risk for OM, this risk being greater the more premature the birth was. None of the other studies, including ours, found prematurity to be a risk factor.
‘Meconium-stained amniotic fluid’ has been studied as a risk in developing OM, using varying definitions and subsequently finding conflicting results [27–29]. Overall, these studies, including ours, did not find the mere presence of meconium-stained amniotic fluid to be a risk [27, 29]. A recent study [28], using the stringent definition of meconium-stained amniotic fluid being present at birth with pulmonary aspiration requiring tracheal suction and treatment at a neonatal intensive care unit, did find an increased risk for AOM. That study mentioned that the mechanism was obscure but presumably related to immune immaturity, although it might also be related to treatment.
Sucking and eating
The items ‘sucking is weak’ and ‘slow-to-feed’ could be seen as symptoms of nasal congestion and/or adenoid hypertrophy, being proxies for mouth breathing, but more appropriate questions to ask in the child under 6 months. These items were not predictive overall for referral and there were no studies for comparison.
Sleeping position
Sleeping in the prone position has been reported as an increased risk for coughing, earache and hearing problems in the young infant [30] or for ‘having ear infections’ and developing a ‘stuffy nose at 6 months of age’ [31]. In our study however, it may not have emerged as a risk, as the number of children sleeping prone was too few to detect a difference at statistical significance.
Heating of the house
We found no studies on ‘heating of the house’, which could reflect socioeconomic status, general environmental stress or indoor air quality. The effect of using secondary home heating sources (a fireplace, wood-burning stove, kerosene heater or a gas stove) has been studied before in developing AOM [32]. Neither in that study nor in ours was a significant association found. Although indoor air quality does seem to affect URTI [33] and hence possibly OM, the absence of central heating in the Netherlands is too rare to detect any such effect.