3.1.1
Overview
The subjects of this thesis consist of 2,638 children who were enrolled at the H.A. Leeper Clinic IHP site between 2002 and August 2011. These subjects were referred to the IHP through several different routes, and are classified according to the outcome of their hearing assessment or surveillance testing as either normal hearing, or hearing impaired. Of this total, 2,390 children were determined to have normal hearing. Gender was recorded for the normal hearing population, with 31.9% (n=763) males, 25.4% (n=608) females, and 42.6%, (n=1,019) of unknown gender. Unknown cases were those for which gender data were missing for the “gender” field in the electronic database. Conversely, 248 cases were identified with hearing loss. More than half of the children identified by the IHP database with hearing loss (n=248) were male (62.9%; n=156) and 37.1% (n=92) were female. Table 2 depicts the distribution of gender for both hearing- impaired and normal hearing cases.
Table 2
Study Population Based on the Electronic Database
Note. Percentage totals may not add to 100 due to rounding.
3.1.2
Referral Routes
Based on data retrieved from the electronic database, 2,638 children were referred to the IHP through a variety of different routes and subsequently enrolled in the IHP at the H.A. Leeper Clinic during the study period 2002-2011. The study sample was broken down into two groups based on the referral route and also on the outcome of their
audiological assessment: Normal Hearing (n=2,390) and Hearing Impaired (n=248). The definition of hearing outcome was based on the IHP protocol definition of normal hearing [Appendix B].
There were five different referral routes to the IHP, and the sample was divided into five groups: Newborn Hearing Screen Fail (NHSF), IHP Surveillance (SURV), IHP Reactivation (REACT), IHP Transfer In (TRANS), and External Referrals (EXT). Table 3 is a summary of the study sample, showing both the referral route into the IHP, and the hearing outcome for each Referral group.
Study Population Hearing-impaired cases Normal hearing cases Total Total 248 2,390 2,638 Males 156 (62.9%) 763 (31.9%) 919 (34.8%) Females 92 (37.1%) 608 (25.4%) 700 (26.5%) Unknown 0 (0.0%) 1,019 (42.6%) 1,019 (38.6%)
Table 3
An Overview of the Electronic Database by Referral Group Referral Source groups Hearing-impaired group total Normal hearing group Total NHSF 143 550 693 SURV 23 1,536 1,559 REACT 31 101 132 TRANS 22 56 78 EXT 28 132 160 Missing Data* 1 15 16 Grand Total 248 2,390 2,638
*Note. Data not entered in the electronic database. Note that percentages may not add up to 100% due to rounding.
The majority of the sample was referred to the IHP for audiological surveillance, with 59.1% (n=1,559/2,638) of the sample in the SURV group. The NHSF group, assessed because they failed their newborn hearing screening, has the second largest number of children referred, with 26.3% (n=693/2,638). Those who entered the IHP by other routes, the EXT, REACT, and TRANS groups constitute the remainder of the study sample: EXT have 6.1% of the total (n=160/2,638), REACT at 5.0% (n=132/2,638), and TRANS with 3.0% (n=78/2,638). Data for referral route and audiological assessment were essentially complete; only 0.6% of the study sample had missing data in the “Referral group” field in the electronic database.
Figure 2 depicts the number of cases identified with hearing loss by the total number referred for each group. The hearing outcome for SURV, the largest Referral group, enrolled in the IHP for audiological surveillance, revealed a low detection rate, with only 1.5% of cases identified with permanent childhood hearing loss (SURV: n=23/1,559). One of the main objectives of this research is to examine the
effectiveness of the IHP Surveillance Program. The data in Table 3, particularly the 23 SURV cases as a fraction of the total (1,559), if extrapolated to a provincial total, could indicate the number of potential beneficiaries of surveillance. For the NHSF Referral group that failed neonatal hearing screening, the audiological testing outcome more frequently revealed a hearing impairment, with 20.6% (n=143/693) identified with a permanent childhood hearing impairment. For the EXT and REACT Referral groups, the detection rate for hearing loss was also high at 17.5% (28/160) and 23.5% (31/132) respectively, suggesting that the policy of accepting referral from the community is an appropriate means of detecting cases missed by neonatal screening, or those with emerging postnatal hearing losses.
In summary, these data illustrate that the majority of children referred to the IHP at the H.A. Leeper Clinic site had a normal hearing outcome on audiological assessment (Figure 2). Although the SURV group received the highest number of referrals, the vast majority in this Referral group, were normal hearing, despite having at least one risk factor; 98.5% were discharged from audiological surveillance with a normal hearing outcome. For the second largest Referral group, NHSF, 79.4% (n=550/693) did not have hearing loss, based on the outcome of their complete audiological assessment, despite failing the neonatal hearing screening.
Figure 2. An Overview of Referral Source Category Data.
3.1.3
Risk Factor Data
Hearing risk factor presence/absence data were extracted using this data field in the electronic database and results were analyzed. For those subjects with data available in the electronic database, 46.2% of those children with normal hearing were identified with a risk factor (n=1,103/2,390), whereas only 5.2% did not have a known risk factor (n=124/2,390). In the hearing-impaired group, 66.1% were identified with at least one risk factor (n=164/248), and 27.8% (69/248) did not have a known risk factor.
However, data from the risk factor field of the electronic database were missing for a significant proportion of the sample. The normal hearing group was missing 48.7% (n= 1,163/2,390) of the risk factor data and the hearing-impaired group was missing less with 6.0% (n =15/248). In many cases, this data field may have been empty because the hearing risk factor status was inferred from other data fields. For the SURV group (n=599), it is required that, based on the IHP protocol, all of these cases have at least one
risk factor present. Furthermore, the 24 cases that were defined as not having a risk factor in the electronic database are presumed to be data entry errors.