Our data illustrate that OM incidence in infants at or before the age of 6 months was higher in the Little Ears cohort than in a predominantly White cohort followed in the Minnesota Twin Cities area in the mid-1990s (63% vs 48%).7
Diagnostic criteria for OM and mean number of study or clinic visits by the age of 6 months were similar in Little Ears and an earlier cohort7
(7 and 6 visits, respectively).
We investigated compliance with study visits because of the obvious dependence of OM diagnoses on completion of ear examinations. Women and infants who complied with the study visit criteria completed more clinic visits as well, increasing the likelihood of OM being diagnosed. The difference in OM rates between infants whose mothers were compliant and those whose mothers were noncompliant suggests that OM may actually have been underdiagnosed in the study population. Study visit compliance was not a risk factor for OM but was related to likelihood of OM detection. Infants whose mothers were noncompliant may have been as likely as infants whose mothers were compliant to experience an OM episode but less likely to have it detected because they underwent fewer examinations.
Regular ear examinations would allow detection of asymptomatic episodes of OM, which occur frequently in the first year of life.4
Prospective studies involving more frequent examinations have reported higher OM rates than have studies involving fewer examinations,1,2,20
and 1 study reported that rates of acute OM were higher among American Indian children living within 5 miles (8 km) of an IHS health facility than among those living farther away, suggesting that access to care increases OM ascertainment.21
Maternal OM history was significantly related to early OM in this study and in an earlier study.7
This relationship suggests a possible role for genetic factors in early OM or greater awareness of OM leading to increased care seeking and more frequent diagnoses (i.e., detection bias). A study conducted on an Apache reservation reported a significantly greater-than-expected concordance of tympanic membrane scarring in first-degree relative pairs, a finding consistent with a genetic hypothesis.22
We did not find that compliance with study visits was related to maternal OM history. However, infant OM would be diagnosed more frequently if mothers with a history were more likely to seek medical care for a symptomatic child. Reported maternal OM history was not validated against medical records, but women were queried about their own history of chronic and recurrent OM. In a study of college students, κ agreement values between self-report and medical record data were 0.53 for number of physician visits related to ear problems and 0.78 for tympanostomy tube placement.23
Previous studies have shown that URIs increase OM risk.6,7
The interaction between URI and study visit compliance observed here suggests that OM was diagnosed independent of previous URIs among infants with more clinic visits. OM episodes not associated with previous URIs may have been milder and therefore not brought to the attention of physicians by noncompliant mothers. Mild episodes would have been more likely to be detected in compliant families who used health services more frequently. Viral respiratory infections promote the development of OM by releasing inflammatory mediators, increasing nasopharyngeal colonization, and suppressing immune defenses; exposure to other children increases the likelihood of colonization and infection with the viruses associated with OM.8,24
Although often observed and potentially modifiable OM risk factors such as short breast-feeding duration and exposure to cigarette smoke were common in this study, they did not influence early OM incidence. The reason that there was not a significant relationship between OM and smoke exposure may have been the relatively small number of cigarettes per day smoked by study mothers or the lack of a truly unexposed group, given that infant exposure to environmental tobacco smoke was common.
Some studies have shown that longer breast-feeding durations and exclusive breastfeeding decrease OM risk,10,25,26
but others have shown that short breast-feeding duration has no effect on OM in early life.27
Early OM rates were similar among infants with and without these 2 are protective factors and 1 is a risk factor, so inadequate power is an unlikely explanation for the lack of association between these factors and early OM. However, if infants of women who smoked and did not breast-feed had fewer clinic visits, OM may have been underascertained, resulting in a lack of association between these risk factors and early OM.
Women’s levels of knowledge about modifiable OM risk factors varied. Their prenatal belief that steps could be taken to prevent infant OM did not predict their postnatal breastfeeding and smoking behaviors. Lawlor et al. suggested that members of disadvantaged groups consider smoking to be an acceptable risk because they are more concerned about addressing immediate dangers (poor housing conditions, environmental and occupational hazards) they view as more proximate threats than smoking.28
Discrepancies between knowledge about healthy behaviors and actual healthy behaviors has long been acknowledged by health educators and has given rise to the concept that knowledge alone is not sufficient for behavior change. Strategies intended to change health behaviors must incorporate intrapersonal, interpersonal, institutional, community, and policy factors.29
Data collected prospectively in 2 Minnesota studies involving similar methods revealed higher OM rates in Little Ears than in a sample derived from a health maintenance organization.7
The present findings are also consistent with higher rates of OM-associated outpatient visits and hospitalizations reported among American Indian/Alaska Native children than among other US children.5
The majority of OM studies involving American Indian samples has been conducted in Navajo and Apache communities. To our knowledge, this is the first study of OM in a predominantly Ojibwe sample, and our findings may not be generalizable to other tribes.
In addition, women who took part in the Little Ears Study may not have been representative of all eligible women at the study sites. Nevertheless, results from Little Ears are similar to data reported by the Minnesota Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and the Bemidji Area IHS on Minnesota rates of breast-feeding and smoking during pregnancy.30,31
Breast-feeding initiation rates among mothers served by WIC in Minnesota were 60% to 68% between 1998 and 2001, as compared with 58% among participants in Little Ears.30
In the Bemidji IHS service area, 41% of women smoked during pregnancy during 1996 through 1998, in comparison with 45% in the Little Ears Study.31
Participants lost to follow-up were more likely to be smokers and to be urban residents. Because OM rates did not vary according to level of environmental tobacco smoke exposure, the overrepresentation of smokers in the group lost to follow-up should not have affected rates of early OM.
In conclusion, OM onset occurred before 6 months of age in nearly two thirds of infants in the Little Ears cohort, but OM may actually have been underdiagnosed in this study, particularly among infants whose mothers did not comply with study visit criteria. URI was the only potentially modifiable risk factor identified. The significant relationship observed between maternal OM history and infant OM may have been due to genetic predisposition or to increased likelihood of detection resulting from maternal awareness of OM and its symptoms.
Although smoke exposure and short duration of breast-feeding were not related to early OM in this study, they have been reported as OM risk factors in other epidemiological studies. Women’s prenatal knowledge and attitudes regarding OM risk were not concordant with their postnatal behaviors. Interventions designed to reduce OM risk factors should focus on barriers to change as well as community, cultural, and policy influences (e.g., health insurance coverage providing regular access to preventive and health care visits).