1
January – December 2003
National Audiology Centre
98 Remuera Rd
Auckland 5
June 2003
ISSN: 1174-44170
Contents
Executive Summary...... 3
Introduction...... 4
Notification and Reporting Criteria...... 5
Database Results...... 6
Degree of Hearing Loss...... 8
Other Disabilities...... 9
Cause of Hearing Loss...... 10
Unilateral Hearing Loss...... 11
Age of Identification of Hearing Loss...... 12
Reasons for Delay in Confirmation...... 14
Risk Factors...... 15
Ethnicity and Hearing...... 16
Persons Suspecting and Confirming Hearing Loss...... 18
Location of Children...... 20
Age of Identification by Region...... 23
References...... 24
Executive Summary
Statistics from the New Zealand Deafness Database show the average age of identification of a moderate or greater degree of hearing loss was 46.1 months in 2003. This is higher than in 2002 when the average age of detection was 35.1 months. The internationally recommended age of identification of a hearing loss is three months with intervention commencing by six months(Joint Committee on Infant Hearing, 2000). The trend to later identification in 2003 is significant and shows a reversal of the trend over the past two years.
The Deafness Database statistics on the age of identification have continued to demonstrate that use of the “at- risk” register for detection of permanent hearing loss in infants results in poor coverage and late age of identification. The data produced in this year’s report also shows the average age of suspicion to have increased from last year. The difference between age of suspicion and age of confirmation has remained fairly constant from the previous year. The initial suspicion of a hearing loss by Well Child Providers still appears to be poor. In 2003 nearly half of all of hearing losses reported were suspected by parents or Vision and Hearing Technicians.
In this years Deafness Database report Maori and Pacific Island children continue to be over-represented in the data and reported later compared to European children. The high rate of Otitis Media with Effusion may contribute to the delay of confirming the hearing loss in this population (Pellow, Blais and McNeil, 1998).
This year’s data shows over-representation in the Auckland region with 36% of notifications coming from this region and with Census data indicating 31.8% of the population residing here. Areas that were under-represented compared to the 2001 Census data, were Waikato and Canterbury.
In this year’s report the average age of identification across the different regions in New Zealand was compared over a 5-year period 1998–2003. The data demonstrates a 29-month range in age of identification from 53 months in the Bay of Plenty to 22 months in South Canterbury. There have been 584 notifications over the 5-year period making an average of 116 notifications per year of moderate or greater degree of hearing loss.
Introduction
Deafness Notification statistics are collected nationally when a child is confirmed with a hearing loss. An initial referral of suspicion is forwarded to an Audiologist and a hearing assessment undertaken. Audiologists overall have continued to confirm the majority of the hearing losses in New Zealand.
Currently New Zealand uses a high-risk register to identify babies who have factors likely to make them at risk for hearing loss. The child’s Well Child Provider should refer any baby presenting with one or more risk factors for a hearing assessment. Hearing loss in infants is usually confirmed using Auditory Brainstem Response Testing (often in conjunction with Otoacoustic Emission and behavioural testing). In older children behavioural techniques are used.
With newborn hearing screening programmes becoming more widely implemented questions are often asked about the deafness notification data and how it relates to likely outcomes from screening programmes. The notification data produce the number of children reported to the database in a calendar year; the data will be made up of children born over a number of years. It is not the number born with hearing loss in any one year. In the case of hearing loss the true incidence of permanent congenital hearing loss would be the number of children born with hearing loss in any one year. Prevalence rates for hearing loss at birth – the number of children who have congenital hearing loss in the population – can be estimated from the database statistics over a number of years.
In recent years the number of notifications has increased leading to reporting becoming more accurate. This has been due in part to a substantial rise in the number of children with mild hearing loss reported. More accurate incidence and prevalence data will be obtained if there is a high quality reporting system associated with a universal newborn hearing screening and subsequent hearing surveillance programme in place.
Notification and Reporting Criteria
In the year 2003, 310 children were reported to the Deafness Detection Database. Of this number, 144 met the audiometric criteria for inclusion in the report. This figure is higher than last year 2002 (n=113) and slightly less than were reported in 2001 (n=158).
The notification criteria is:
“Children under 18 years with congenital hearing losses or any hearing loss not remediable by medical or surgical means, and which require hearing aids and/or surgical intervention. They must have an average bilateral hearing loss (over four audiometric frequencies 500-4000Hz), greater than 26dBHL in the better ear (Northern and Downs classification 1984).”
Since the Database relies on Audiologists notifying hearing losses and the cause of hearing loss is often unknown at the time of completing the notification form it is likely that a small percentage of acquired hearing losses are also included in the reported data. Those known acquired losses are removed from the database prior to analysis.
Those children reported in 2003 who did not meet the criteria and were not included in the report were:
- 73 with slight hearing losses (<26dBHL)
- 51 with unilateral hearing losses
- 43 with acquired[1] hearing losses
- 36 who were born overseas
In some cases these exclusions were in more than one category, e.g. child with acquired loss born overseas[2] The number of children notified to the Database has risen substantially since 1982 when the Database began collecting information. Figure 1 shows a trend of increased number of notifications. Last year in 2002 the number of children reported was 286 and in 2001 over 400 children were notified. The high number in 2001 was due in part to a large amount of retrospective reporting by some regions in that year.
Figure 1: The number of children notified to the Deafness Database from 1982 to 2003
Database Results
Figure 2 shows the degree of hearing loss for the 144 children notified in 2003, by birth year. The increase in the number of children detected with a hearing loss in 1997 corresponds to the years when current 5 and 6 year olds were born. The increase in detection of hearing loss at this age can be attributed to the Vision and Hearing Screening Programme, which screens the hearing of all new school entrants. This graph shows a similar pattern to previous years.
There were 26 children in 2003 that were born prior to 1994. This figure is considerably higher than last year (2002) with 18 children being born before 1993. These late notifications were for a number of reasons including lack of parental suspicion of hearing loss despite children having no speech and language at five years of age or older. Several children also were suspected of having a hearing loss at birth, however were not initially referred until a lot older by the Public Health Nurse. Several children also did not attend appointments and therefore had to be re-referred for Audiological assessment. One child also was confirmed at 168 months and despite the hearing loss thought to have been present at birth was not picked up until this
age. The reason given was no screening tests being performed at an early age.
Figure 2: Degree of hearing loss for children notified in 2003 as a function of birth year (n=144).
Figure 3 below shows the age distribution for identification of hearing loss as a cumulative percentage for the years 2000-2003. The year 2003 data is very similar to that obtained in previous years, however is slightly below that obtained last year in 2002.
Figure 3: Cumulative percentage of children reported to the Database from 2000 to 2003 in 10 month age brackets
Degree of Hearing Loss
The classification for the degree of hearing loss used in this report is based on the Northern and Downs classification (1984). The degree of hearing loss is based on the better hearing ear, and is an average of the pure-tone thresholds at 500, 1000, 2000 and 4000Hz.
The divisions for the degrees of hearing loss are:
- Slight16-25dBHL ( These children are not included in the analysis)
- Mild26-40dBHL
- Moderate41-65dBHL
- Severe66-95dBHL
- Profound>96+dBHL
Figure 4 shows the percentages recorded for each degree of hearing loss in 2003. The percentages are very similar to those reported in the year 2002 (mild 47%, moderate 35%, severe 10%, profound 8%). The data for 2003 is mild 56% (n=80), moderate 33% (n=48), severe 6% (n=9), profound 5% (n=7).
Figure 4: The percentages for the degree of hearing loss in the better hearing ear (n=144).
This data can be compared to the results from Australian Hearing Report March 2003:
Degree of Hearing Loss / Mild(26-40dBHL) / Moderate
(41-65dBHL) / Severe
(66-95dBHL) / Profound (>95 dBHL)
New Zealand / 56% / 33% / 6% / 5%
Degree of Hearing Loss / Mild
(<30dBHL) / Moderate
(31-60dBHL) / Severe
(61-90dBHL) / Profound
(>90 dBHL)
Australia unidentified = 5% / 36% / 36% / 12% / 11%
Table 1: Percentage of children with various degrees of hearing loss in New Zealand and Australia.
Other Disabilities
Figure 5:Other handicaps (apart from hearing loss) for the children notified in 2003 (n=144).
Figure 5 shows that the majority of children notified in 2003 were reported as having no other disabilities (79%). This is consistent with data from previous years. The only figure of note which has increased is the category described as “multiple”. Last year (2002) 5% of children with a hearing impairment were described as having multiple problems. This year an increase is seen with 11% of children having multiple problems. The types of multiple problems in the database include Pfeiffers Syndrome, lung/breathing problems and developmental delay, Waardenburg’s Syndrome, Cri du Chat Syndrome, Downs Syndrome, Foetal Alcohol Syndrome, Stevens-Johnson Syndrome, cerebral palsy and epilepsy, and also other chromosomal abnormalities.
Cause of Hearing Loss
As with previous years, the primary cause for bilateral hearing loss in 2003 was reported as unknown (59%). This is similar to 2002 when 56% of the notifications were reported as unknown but higher than Australian Hearing (2003) who report 48.5% as unknown.
Figure 6: Causes of hearing loss identified for the children notified in 2003 (n=114).
Family history is still the second most common cause of hearing loss given this year accounting for 24% of the children notified, very similar to last year with 25% of notifications in 2002 being due to family history.
In recent years the use of the term “family history” as a cause of hearing loss has been questioned and a term that is now in more common usage is hereditary hearing loss to refer to those losses that are of genetic origin. The use of the term family history may give rise to an over reporting of this factor as a cause as some parents may report cases of acquired hearing loss as “family history”. This category is significantly higher than Australian figures (AHS 2003), which states there is familial aetiology in 8.8% of cases. However the Australian figures are not directly comparable to the New Zealand figures as they include some significant additional mainly acquired categories (Conductive 19%, Meningitis 2.6%, Other 15.7%) and are a data set collected at hearing aid fitting. (AHS 2003).
Unilateral Hearing Loss
Figure 7: Cause of unilateral hearing loss (n=312).
This report is primarily concerned with bilateral hearing loss, but as unilateral data is also reported to the database, this graph is included. As the number of unilateral hearing losses reported is small this graph relates to the years 1975 to 2003. In the year 2003 there were 51 cases of unilateral hearing loss reported to the database. Last year (2002) 38 cases were reported and in 2001, 54 cases of unilateral hearing loss were reported.
The incidence of unilateral hearing loss is predicted to be one in every 1000 births using estimates from established American Newborn Screening programmes (Yoshinaga, 2001). If there are approximately 55,000 births per year in New Zealand, approximately 55 babies each year will be born with a unilateral sensorineural hearing loss. This suggests that there is a significant percentage of unilateral hearing losses are now being reported to the Deafness Database.
As with bilateral hearing loss the cause of the hearing loss is unknown in a significant proportion of cases (43%).
Age of Identification of Hearing Loss
The average age of identification of hearing loss is the figure most commonly quoted from the database and show the average age of confirmation of hearing loss that are at least moderate in degree. Although the detrimental effects of “mild” hearing loss on educational achievement are now recognised, this category has traditionally been excluded from the age of identification data. The inclusion of data on mild hearing loss would skew the results as mild hearing losses are detected much later. The negative effect of mild degrees of hearing loss on educational outcomes has only recently been recognised (Bess et al., 1998).
The hearing loss classification that was historically used to produce this graph (Degree 1) has been superseded. However we continue to show the results from the two classification systems to allow comparison to earlier data:
- Degree 1 is the classification system for degree of hearing loss used by the Database prior to 1996, Mild=30-55dBHL, Moderate/Severe=56-85dBHL and Profound 86dBHL. (This meant only losses greater than PTA 55dB were reported in this graph).
- Degree 2 is the classification system [3] (outlined on page 8) used since 1996. (Losses > 40dB HL are included in this graph).
Figure 8 and Table 2 show this year the average age of identification of a moderate or greater bilateral permanent hearing loss using the degree 2 classification is 46.1 months. The average age using the Degree 1 classification system is 33.7 months for a hearing loss notified in the better hearing ear of greater than 55dBHL. This year’s results indicate an increase from previous years. In 2002 the average age of identification using the Degree 2 criteria was 35.1 months and Degree 1 was 23.8 months. This shows a worsening of the age of detection by 11 months from 2002.
Table 2 compares mean, median and interquartile ranges for age of identification of a moderate or greater hearing loss in 2002 and 2003.
Year / Average (mo) / Median (mo) / Interquartile range (mo)2003 / 46.1 / 41.5 / 16-69
2002 / 35.1 / 30 / 15-58
Table 2: Comparison of average, median and interquartile range for Degree 2 hearing loss in past two years.
Figure 8: The average age of identification of at least a moderate degree of hearing loss since 1982.
The average age of identification varies greatly with the degree of hearing loss and this can be seen graphically and in a table form in Figure 10 and Table 4, where this information is considered in terms of risk factors. In 2003 the average age was 69.5 months for a mild loss, 52.6 months for a moderate loss, 28.1 months for a severe loss and 22.6 for a profound loss.
Table 3 shows the mean ages of suspicion and confirmation of at least a moderate hearing loss over the past three years. In this table all data is presented using the Degree 2 classification.
In 2003 the age of suspicion of a hearing loss has increased from last year with the average age of suspicion being 35.3 months. This is an increase of 10.9 months from 2002 when hearing loss was first suspected at 24.4 months. This year the average time taken from suspicion to confirmation was 10.8 months, this is similar to last year when it took 10.7 months.
Year / Suspected / Confirmed / Time Taken in Months2003 / 35.3 / 46.1 / 10.8
2002 / 24.4 / 35.1 / 10.7
2001 / 28.1 / 33.7 / 6.5
Table 3: Mean age (months) of suspicion and confirmation of a moderate or greater hearing loss for years 2001-2003
Reasons for Delay in Confirmation
A significant delay[4] between suspecting and confirming a hearing loss is longer than six months. Figure 9 shows that, for the year 2003, 55% of hearing losses identified to the Database had no delay in confirming this loss. This is very similar to last year when 59% of hearing losses had no delay. The factors contributing to a delay in confirmation of hearing loss are reasonably consistent with previous years except for a significant increase in delay due to “waiting list issues”. This year (2003) 7% had delay due to waiting lists compared to 2002 when only 1% of delay was due to the waiting list. This may be explained by a shortage of public service Audiologists particularly at the Manukau Super Clinic from whom we received a large number of notifications in 2003.
Figure 9: Reasons for the delay in confirming hearing losses in 2003 (n=114).
Risk Factors
Figure 10: Age of identification for mild (26-40dBHL), moderate (41-65dBHL), severe (66-95dBHL) and profound (>95dBHL) degrees of hearing loss according to risk factors.
Figure 10 and Table 4 show the age of identification related to the presence of risk factors for hearing loss. The children with mild and moderate hearing losses who had risk factors were confirmed earlier than those without risk factors. For severe and profound losses the presence of risk factors has little effect on the age of identification. Often those children in the profound categories have multiple and severe health problems and therefore other issues take priority over the identification of hearing loss.
Degree / Risk / Nonrisk / OverallMild / 59.7 / 75.5 / 69.5
Moderate / 40.9 / 61.5 / 52.6
Severe / 26.2 / 30.0 / 28.1
Profound / 25.5 / 19.7 / 22.6
Table 4: Age of identification in months categorised into degree of hearing loss and presence of risk factors.
The risk factor criteria is designed to be applied in early infancy by Well Child Providers. The presence of risk factors should prompt a referral to audiology for assessment. Clearly they are not being applied as recommended by the Well Child Schedule.
Ethnicity and Hearing
The breakdown of ethnicity for children notified with hearing loss in 2003 is shown in Figure 11.
This figure shows that Maori children made up nearly half the number of notifications in 2003 (46%). 17% of those notified were categorised as Pacific Islanders. Those listed as Asian which accounted for 3% included one Filipino child born in New Zealand, and three children of Indian descent. European children accounted for the second largest category in this year’s data making up 34% of the notifications. This is similar to last year where 39% were reported as of European descent.