Bod Hearing Loss

1 Global Burden of Disease 2000

Global burden of hearing loss in the year 2000

Colin Mathers1, Andrew Smith2, Marisol Concha3

1. Introduction Hearing impairment is the most frequent sensory deficit in human populations, affecting more than 250 million people in the world. Consequences of hearing impairment include inability to interpret speech sounds, often producing a reduced ability to communicate, delay in language acquisition, economic and educational disadvantage, social isolation and stigmatisation. It may be worsened by some medical conditions such as hypothyroidism, diabetes, and possibly hyperlipidemia, among others.

Most congenital and childhood onset hearing loss is included as sequelae to various disease and injury causes already included in the Global Burden of Disease Study. Examples include otitis media, memingitis, rubella, congenital anomalies and non-syndromal inherited hearing loss. Adult-onset hearing loss was not separately analysed in the original Global Burden of Disease for 1990 (1). The leading causes of adult-onset hearing loss are presbycusis (age related hearing loss) followed by noise-induced hearing loss. This paper reviews global data on hearing loss among children and among adults, and estimates the global burden of adult-onset hearing loss. In addition, it provides estimates of the prevalence of hearing loss among children and adults at various levels of severity.

In the Version 1 estimates for the Global Burden of Disease 2000 study, published in the World Health Report 2001 (2), adult-onset hearing loss was the 2nd leading cause of YLDs at global level, accounting for 4.6% of total global YLDs. This paper summarises the data and methods used to produce the Version 3 estimates of adult-onset hearing loss burden for the year 2000, as published in the World Health Report 2003.

2. Case and sequelae definitions There is a diversity of definitions of hearing impairment, thus, comparison among studies is difficult. We use WHO classification that classified hearing impairment according to the pure tone average in the better hearing ear. Categories of hearing impairment ranges from “no impairment” to “profound impairment” according the threshold level. The hearing threshold level, using audiometry, is to be taken as the better ear average for four frequencies 0.5, 1, 2, and 4 kHz. (3) The different grades of hearing impairment and their impact in performance are presented in Table 2.1. Duivestijn (4) discusses the effect of different definitions on measured prevalence of hearing loss.

1 Epidemiology and Burden of Disease, WHO Geneva (GPE/EBD) 2 Prevention of Blindness and Deafness (MNC/PBD), WHO Geneva 3 Ministry of Health, Chile


Table 2.2 summarizes the GBD 2000 case and sequelae definitions for adult-onset hearing loss. For the GBD 2000, the burden of adult-onset hearing loss has been estimated for moderate or greater hearing impairment. While the prevalence of slight impairment (26-40dBHL) has also been estimated, it has been assumed to have negligible disability weight and not to contribute to the YLD for hearing loss. Table 2.1 WHO grades of hearing impairment

Grade of Impairment

Audiometric ISO value (average of 500, 1000, 2000, 4000 Hz) Impairment description

0 (no impairment) 25 dBHL or less (better ear) No or very slight hearing problems. Able to hear whispers

1 (Slight impairment) 26-40 dBHL (better ear) Able to hear and repeat words spoken in normal voice at 1 metre

2 (Moderate impairment) 41-60 dBHL (better ear) Able to hear and repeat words using raised voice at 1 metre

3 (severe impairment) 61-80 dBHL (better ear) Able to hear some words when shouted into better ear

4 (Profound impairment including deafness)

81 dBHL or greater (better ear) Unable to hear and understand even a shouted voice

Source: (3)

Table 2.2 GBD 2000 case and severity-level definitions for adult-onset hearing loss

Cause category GBD 2000 Code ICD 9 codes ICD 10 codes

Adult-onset hearing loss U102 389 H90-H91

Severity level Definition

Hearing loss, adult onset Cases of adult onset hearing loss due to ageing or noise exposure. Excludes hearing loss due to congenital causes, infectious diseases, other diseases or injury.

Moderate hearing loss Hearing threshold level in the better ear is 41-60 dBHTL (averaged over 0.5, 1, 2, 4kHz). (Not able to hear and repeat words spoken in normal voice at 1 metre). Person may or may not use a hearing aid

Severe hearing loss Hearing threshold level in the better ear is 61-80 dBHTL (averaged over 0.5, 1, 2, 4kHz). (Not able to hear and repeat words using raised voice at 1 metre). Person may or may not use a hearing aid

Profound hearing loss Hearing threshold level in the better ear is 81 dBHTL or more (averaged over 0.5, 1, 2, 4kHz). (Not able to hear words when shouted into better ear). Person may or may not use a hearing aid

3. Population prevalence and incidence studies In spite of the number of published studies about hearing impairment (HI), the currently available data is mostly incomplete and use different criteria, which causes difficulties in comparison and estimation of the problem. Also, only relatively few studies have been carried out to date in representative population samples. Table 3.1 shows the prevalence of hearing impairment measured


by pure tone audiometry in countries with available information. Population-based surveys conducted in several developing countries have used the protocols developed by WHO to identify causes of HI and prevalence.

Available data on hearing loss prevalence in children are summarized in Table 3.2.


Table 3.1. Prevalence studies for hearing impairment: adults

Country Study population Ref. Years Definition used

Sample size Age range

Prevalences available by

UK Four cities (5,6) 1980-86 25+, 45+, 65+ dBHL in better ear

2,910 17-80 Age, sex

Italy Milan, Padua, Florence, Bari, Palermo

(7) 1989 25+, 45+, 65+, 90+ dBHL in the better ear

2,170 18+ Age

Denmark Copenhagen - males

(8) 1976 25+dBHL in better ear 0.5,1,2,4)

300 49-69 Age

Denmark Jutland (rural) (9) Early 1990s

25+ dBHL

35+ dBHL

45+ dBHL,

1,397 31-50 Age x sex

Finland Northern Ostrobothnia

(10) 1997 21+, 40+, 70+, 95+ dBHL in the better ear (0.5,1,2,4)

5,400 5-75 Age

USA Framingham (11) 1979 25+ dBHL (0.5,1,2,4 kHz) in better ear

2,293 57-89

USA Beaver Dam, Wisconsin

(12-14)

1993-95 26+, 41+, >60 in WORSE ear (0.5,1,2,4 kHz )

>25 dBHL in better ear (0.5,1,2,4)

3,753 48-92 Age x sex (26+ only)

USA Beaver Dam, Wisconsin

(15-16)

1987-88 26+, 41+, >60 in WORSE ear (0.5,1,2,4 kHz )

48-92

USA NHANES 1 national

(17-18)

1971-75 25+ dBHL in the better ear (HFPTA scale 1,2,4 kHz)

2,506 55-74 Age x sex

USA HHANES Hispanic Americans

(19) 1982-84 26+, 41+ in WORSE ear (0.5,1,2 kHz )

2,751 20-74 Age x sex

Brazil Residents of the city of Canoas, RS, Brazil

(20) 2003 26+,41+, 61+, 81+ dBHL or, better ear

3,858 All ages Age, sex

Australia South Australia (21) 1996? 25+, 35+, 45+, 65+ dBHL in better ear

0.5,1,2,4)

9,027 15+ Age x sex

Oman National (22) 1996-97 26+, 41+ dBHL (1,2,3 kHz bilateral/better ear)

11,402 All ages Age

India Vellore, Taluk, Tamil Nadu

(23-24)

1997-98 26+,41+, 61+, 81+ dBHL or, better ear

5,432 All ages Age

India Lucknow rural (25) 1975-76 15+, 30+, 60+ dBHL, bilateral deafness and unilateral deafness

904 All ages Age x sex (15+) Age (30+,60+)

India Lucknow urban (26) 1970 15+, 30+, 60+ dBHL, bilateral deafness and unilateral deafness

904 All ages Age x sex (15+) Age (30+,60+)

Sri Lanka Kandy district (23-24)

1998-2000?

27+, 41+, 61+ 81+ dBHL, better ear (1,2,4 kHz bilateral/better ear)

4,858 All ages Age (41+ only)


Nepal Two regions (27) 1990? 31, 51+, 81+ dBHL, better ear (1,2,4 kHz bilateral/better ear)

15,845 5+ years Age

China Sichuan (28-29)

1986-87 27+, 56+, 91+ dBHL, better ear

126,876 All ages

Age, sex (27+ only)

Korea Community-based and health clinics

(30) 1994-97 27+, 41+, 56+, 71+ dBHL, both ears; presbycusis only

39,004 25+ Age x sex Age (56, 71)


Table 3.1 (continued). Prevalence studies for hearing impairment: adults

Thailand 17 provinces (31) 1988-90 41 dBHL, better ear 7,499 All ages

Thailand Bangkok + 5 provinces

(31) 1986-87 41+, 61+, 81+ dBHL, better ear (0.5, 1, 2 kHz bilateral/better ear)

1,797 All ages Total only

Indonesia Bandung municipality & district

(23-24)

1997-98 26+, 41+, 61+ 81+ dBHL, (1,2,4 kHz bilateral/better ear)


Myanmar Yangon (23-24)

1997-98 26+, 41+, 61+ 81+ dBHL, (1,2,4 kHz bilateral/better ear)


Vietnam 6 selected provinces (3 north, 3 south)

(32) 26+, 41+, 61+ 81+ dBHL, (1,2,4 kHz bilateral/better ear)

13,120 6 months and older

Age x sex

Nigeria 3 states: Akua Ibom, Benue, Katsina

(33) 2000-2001

26+, 41+, 61+ 81+ dBHL, (1,2,4 kHz bilateral/better ear)


Standardized prevalence of adult-onset hearing loss

Prevalence studies use different thresholds (and in some cases different definitions in terms of frequencies and better or worse ear) and different age groups. Where non-WHO thresholds used, the prevalence of hearing impairment at the WHO thresholds was interpolated assuming the log of the cumulative prevalence is linear with threshold. This relationship holds reasonably well in most studies.

Where prevalences were not available by sex, the sex ratio from a similar study in the same region was assumed. Prevalences were estimated for GBD age groups and the WHO hearing impairment thresholds. Table 3.3 summarizes these estimates showing age-standardized prevalences for ages 15 and over.

Prevalence of adult onset hearing loss was estimated by subtracting from prevalences at ages 20 and over, the estimated prevalence of hearing loss for teenage children (15-19 years) or the nearest similar age group for which prevalences available. It is assumed that the incidence of adult-onset hearing loss associated with otitis media and other infectious and non-infectious causes included elsewhere in the GBD 2000 cause list is negligible compared to the incidence of adult-onset hearing loss associated with age-related hearing degeneration or noise-induced loss. The estimated prevalence of hearing loss for teenage children is summarized in Table 3.4.

Figures 3.1 and 3.2 summarize the estimated age-standardized prevalences of adult-onset hearing loss at 41+ dBHTL and 61+ dBHTL respectively for the studies listed in Table 3.3. Figure 3.3 shows the range of male/female prevalence ratios for these studies.


Table 3.2 Prevalence studies for hearing impairment: children

Country Study population Ref. Years Definition used

Sample size Age range

Prevalence

%

Developed Review (34) Review 41+ dBHL better ear Childhood 0.05 – 0.23

UK Trent region (35) 1985-1993 40+ dBHL better ear at 0.5, 1, 2, 4 kHz

552,558 0-9 0.133 birth

prevalence4

USA Atlanta (36) 1991-93 40+ dBHL better ear at 0.5, 1, 2 kHz

255,742 3-10 0.11

USA NHANES II and Hispanic HANES

(37) 1982-1984 31+ dB HL better ear 7,888 6-19 African-Am.

Cuban Am.

Mexican Am.

White, non-H.

0.78 1.21 0.60 0.38

USA NHANES III (38) 1988-94 16+, 26+ dB HL at 0.5, 1, 2 kHz better ear

6,166 6-19 0.7 (16+) 0.4 (26+)

Developing Review (34) Review 41+ dBHL better ear Childhood 0.2-0.42

Thailand Bangkok schools Rural schools

(31) ? 41+ dBHL better ear 10,242 2,153

School age Children

3.9 6.1

Sierra Leone Panguma (39) 1992 26+, 41+, 61+ dBHL better ear

2,015 5-15 2.58 (26-40) 0.65 (41-60) 0.50 (61+)

Angola Luanda (40) 1992? 31+ dBHL better ear at .5, 1, 2 kHz

1,030 Schoolchildren 2.0

Zimbabwe (41) 1970s 31+ dBHL better ear 885 Schoolchildren 3.3

Kenya Kiambu district

(42) 1990? 31+ dBHL better ear at 2 & 4 kHz

5,368 Primary school age

2.2

Tanzania Northern inland district

(43) 31+ dBHL either ear at .5, 1, 2 kHz

Severe/profound

854 Primary school age

3.0

0.35

South Africa

Poor rural district in Western Cape

(44) 1990? 21+, 31+, 41+ dBHL better ear

401 6-13 2.0 (31+) 0.5 (41+)

Swaziland 1st year school-children

(44)

Saudi Arabia

Riyadh (45) 1997 20+dBHL, Air cond at .25-.8kHz & .5-4kHz bone cond, unilateral or better ear bilateral

6421 2m – 12y 7.7

4 This figure refers to what the authors call “permanent childhood hearing impairment”– that is sensorineural hearing loss and includes 16% who had post-natally acquired loss. The prevalence rate for congenital hearing impairments was 0.112%. The figures are not directly comparable with data from the WHO studies which include conductive loss.


Table 3.3. Estimated prevalences of adult onset hearing loss for adults aged 15 years and over

Age standardized prevalence (%) Male/Females prevalence ratio

26+ 41+ 61+ 81+ 26+ 41+ 61+ 81+

UK (1) 11.8 4.0 1.1 0.3 1.2 1.1 1.0 0.9

Italy (2) 12.7 4.4 1.3 1.3 1.2 1.1 1.0 1.0

Denmark (3) 12.8 3.5 0.8 0.1 1.9 2.3 1.5 0.8

Finland (4) 7.4 2.3 0.5 0.2 1.4 1.5 1.1 0.9

Australia 11.8 2.6 0.4 0.1 1.9 2.4 1.3 0.7

USA NHANES1 (5) 11.5 3.4 0.8 0.1 1.7 1.6 1.0 0.5

BeaverDam (6) 8.7 2.5 0.6 0.1 2.2 1.6 1.0 0.5

Hispanic (7) 10.0 3.0 0.7 0.1 2.1 1.6 1.0 0.5

China (1) 4.0 2.8 1.3 0.3 1.0 1.0 1.0 1.0

Korea (8) 15.5 2.8 0.3 0.2 1.3 1.5 1.1 1.0

India Vellore (1) 7.6 4.4 2.5 0.8 1.1 1.0 1.0

Vellore 2 (1) 8.0 1.5 0.1 1.0 1.0 1.0

Lucknow Urban (9) 9.8 6.2 3.1 1.5 1.1 1.2 1.0 1.0

Lucknow Rural (9) 7.3 5.6 3.5 2.3 1.0 1.0 1.0 1.0

Nepal (10) 15.3 8.7 4.5 2.5 1.2 1.4 1.4 1.0

Oman (11) 11.2 6.2 3.0 1.5 1.1 1.1

Indonesia (1) 7.1 1.4 0.1 1.5 1.0 1.0

Myanmar (1) 8.6 2.7 0.0 1.2 1.0 1.0

SriLanka (1) 21.7 10.0 3.4 0.5 1.3 1.3 1.0 1.0

Thailand (12) 11.6 2.9 0.9 1.3 1.1 1.1

Nigeria (1) 4.5 1.1

Notes:

(1) Overall sex ratio at each threshold assumed to apply for each age group.

(2) Odds ratio for measured and self -reported hearing loss by sex 1.0; but around 2 for noise exposure which is greater in manual occupations - so possibly a male excess. UK sex ratios used as proxy.

(3) Prevalences for missing age groups estimated using Finnish and Australian age patterns.

(4) Danish sex ratios used for age groups 30-50.

(5) Prevalences extrapolated to all ages 15+ using UK age patterns and sex ratio of 1.56. Prevalence ratio of 26+/41+ assumed to be the same as in the Beaver Dam study.

(6) Prevalences extrapolated to all ages 15+ using Australian age patterns.

(7) Prevalence estimates based on sample-weighted average of prevalences for Mexican and Cuban born Americans. Prevalence of hearing impairment in better ear estimated using ratio for better ear to worse ear from Beaver Dam study. Prevalence adjusted for exclus ion of 4kHz frequency using data from the Framingham study.

(8) Chinese aetiology data from Liu et al. found that presbyacusis was 54% of non-infectious causes. Reported prevalences for presbyacusis adjusted upwards accordingly.

(9) Assumed same proportion bilateral as in rural study: For 15+ dBHTL, 74.3% had bilateral deafness. Unilateral tended to be mild deafness. In the rural study, for unilateral deafness, 96% mild-moderate, while 90% for those with bilateral deafness

(10) Assumed same sex ratios as in India.

(11) Prevalences adjusted for difference in prevalence for 1,2,3 and 0.5,1,2,4 kHz using data from Duijvestijn et al 1999

(12) No age distributions given in Thai study. Age pattern based on average for 4 SEARO countries (Sri Lanka, India, Indonesia, Myanmar).



Table 3.4: Estimated prevalences childhood onset hearing loss at ages 15-19

15+ 26+ 31+ 41+ 61+ 81+

UK 1.00 0.13 0.10 0.10

Italy 1.00 0.13 0.10 0.10

Denmark 1.00 0.10 0.10

Finland 1.00 0.20 0.10

AUS 1.00 0.10 0.10

USA NHANES1 1.00 0.13 0.10

BeaverDam 1.00 0.13 0.10

Hispanic 1.50 0.50

China 1.00 0.15 0.12 0.10

Korea

India (Vellore) 2.00 0.00

India (Vellore 2) 1.58 0.10 0.08

India (Lucknow Urban)

11.50 3.31 1.57 0.22

India (Lucknow Rural

13.10 4.57 2.43 0.35

Nepal 5.57 2.96 2.00 1.00 0.61

OMAN 3.33 0.66 0.10

Indonesia 0.80 0.10 0.08

Myanmar 3.82 0.10 0.05

SriLanka 3.53 0.10 0.10

Thailand 5.40 0.15 0.00

Nigeria 9.3 6.86 3.02 0.93 0.58


0 2 4 6 8 10 12 14

UK

Italy

Denmark

Finland

AUS

USA NHANES1

BeaverDam

Hispanic

China

Korea

India (Vellore)

India (Vellore 2)



Nepal

OMAN

Indonesia

Myanmar

SriLanka

Thailand

Nigeria

Age-standardised prevalence (%) at 41+ dBHLT

Figure 3.1. Estimated age-standardised adult-onset hearing loss prevalence rates, 41+ dBHTL, available population studies.


0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

UK

Italy

Denmark

Finland

AUS

USA NHANES1

BeaverDam

Hispanic

China

Korea

India (Vellore)

India (Vellore 2)



Nepal

Indonesia

Myanmar

SriLanka

Thailand

Age-standardised prevalence (%) at 61+ dBHLT

Figure 3.2. Estimated age-standardised adult-onset hearing loss prevalence rates, 61+ dBHTL, available population studies.


0 0.5 1 1.5 2 2.5

UK

Italy

Finland

BeaverDam

Hispanic

USA NHANES1

Denmark

AUS

China

China



India (Vellore 2)

India (Vellore)

OMAN

Myanmar

SriLanka

Thailand

Nepal

Indonesia

Korea

Nigeria

Male/female ratio at 41+ dBHTL

Figure 3.3. Estimated male/female ratio of age-standardised adult-onset hearing loss prevalence rates, 41+ dBHTL, available population studies.

4. Disease model for adult-onset hearing loss The incidence and average duration of moderate or greater hearing loss (41+ dBHTL as defined in Table 2.2) were estimated for each GBD 2000 epidemiological region from estimates of prevalence by age and sex using the software program DISMOD II, assuming zero remission rate and a relative risk of mortality of 1.

There is conflicting evidence between mortality and hearing loss. In a ten year longitudinal analysis of the NHANES I participants aged 55-74 years at baseline who received hearing examination found than hearing loss predicts mortality: RR = 1.17 (46), however other studies have reported that after controlling by age the association disappear. We assume an RR of 1.0.


Years lived with disability (YLDs) were calculated for the boxes shaded in grey.

Figure 4.1 Adult-onset hearing loss disease model.

Available treatment includes hearing aids, cochlear implants, and lip reading. Cochlear implants5 are used by people with severe and profound hearing impairments who obtain negligible benefit from hearing aids. While cochlear implants result in remission from hearing loss, the use of these is negligible at the population level, and we assume a remission rate of zero. The effect of hearing aid use is modelled as a reduction in the severity of hearing loss, and hence a lower disability weight.

YLD for hearing loss are calculated from estimated incidence, average duration and disability weight (1). Disability weights for hearing loss used in the GBD 1990 study (1) and the Netherlands disability weights study (47) are shown in Table 4.1. The Australian Burden of Disease study (48) used modified Dutch weights together with Australian survey information on severity distribution in the population. The resulting average disability weight is shown in the last column of Table 4.1. Table 4.1 Disability weights for adult-onset hearing loss

Stage/sequela GBD 1990 Netherlands Study Australian Study

Mild hearing loss 0.04 0.02

Moderate hearing loss 0.12 0.12

Severe hearing loss (deafness)

0.333 (indicator condition)

0.37 0.37

All levels 0.216 (untreated) 0.168 (treated)

The global coverage of hearing aid use has been estimated to be no more than 10%, skewed towards developed countries (49). Less than 1% of hearing impaired individuals use hearing aids in developing countries, while in developed countries the rate ranges from 10% to 40% (see Section 5 below). It is thus important to take into account the average prevalence of hearing aid use by region in calculating the average disability weight for hearing loss. Little information is available on the impact of hearing aid use on hearing disability. We provisionally assume that hearing aid use reduces the disability weight to the next lower severity level as shown in Table 4.2. While we give zero

5 It is a device designed to provide sound detection and improved speech understanding

Incidence of HI

Prevalence

Death


disability weight to untreated mild hearing loss, we give a residual weight of 0.04 (the Dutch weight for mild hearing loss) to a person with moderate hearing loss who uses a hearing aid.

These provisional weights will be revised following analysis of the health state valuation data collected in the World Health Survey in 2002-2003. Table 4.2 Provisional disability weights for adult-onset hearing loss, GBD 2000 (Version 2)

Stage/sequela Disability weight Comment

Mild (26-40 dBHTL) untreated 0.00

Moderate (41-60 dBHTL) untreated 0.12 Dutch weight for moderate hearing loss

Severe and profound hearing loss (61+ dBHTL) untreated 0.333

GBD weight for deafness as indicator condition (Dutch weight is 0.37)

Moderate (41-60 dBHTL) with hearing aid 0.04 Dutch weight for mild hearing loss (25-44 dBHTL)

Severe and profound hearing loss (61+ dBHTL) with hearing aid 0.12

Dutch weight for moderate hearing loss (45-64 dBHTL)

5. Treatment for hearing impairment Studies measuring prevalence of hearing aid use were reviewed (5,15,16,19,21,48,50-69) and used to estimate the prevalence of hearing aid use among individuals with hearing impairment (assuming that hearing aid use is confined to moderate impairment levels and greater. The results are shown in Table 5.2 below.

Table 5.2 Estimated regional prevalence of hearing aid use among those with hearing loss, by severity level, age and sex, GBD 2000 (Version 3)

Severity (dBHTL) AMRO A AMRO B AMRO D EURO A EURO B1 EUR B2 EUR C WPRA

Other regions

41-60 Male

15-29 5 0 0 5 5 0 0 0 0

30-44 10 0 0 5 5 0 0 20 0

45-59 20 3 3 10 10 3 3 30 0

60-69 20 3 3 10 10 3 3 30 0

70-79 20 3 3 10 10 3 3 30 0

Female

15-29 5 0 0 5 5 0 0 5 0

30-44 10 0 0 5 5 0 0 10 0

45-59 20 3 3 10 10 3 3 20 0


60-69 20 3 3 20 20 3 3 20 0

70-79 20 3 3 30 30 3 3 20 0

61-80 Male 15+ 50 10 10 50 50 10 10 75 0

Female 15+ 50 10 10 50 50 10 10 50 0

81+ Male 15+ 80 25 25 80 80 25 80 80 0

Female 15+ 80 25 25 80 80 25 80 80 0


Age-sex-region specific estimates of prevalence of hearing loss at each of the severity levels (see Section 6 below) were combined with the estimated prevalence of hearing aid use (Table 5.2) to compute average disability weights by age, sex and region for hearing loss at levels 41 dBHTL and higher. The average disability weights thus vary by age and sex across regions. The resulting average disability weights are summarized below in Table 5.3.

Table 5.3 Estimated average disability weight for ages 15+, by subregion and sex

Subregion Male Female Subregion Male Female

AFRO D 0.19 0.20 EURO B2 0.17 0.17

AFRO E 0.19 0.20 EURO C 0.16 0.16

AMRO A 0.13 0.14 SEARO B 0.15 0.17

AMRO B 0.15 0.17 SEARO D 0.16 0.16

AMRO D 0.15 0.17 WPRO A 0.11 0.14

EMRO B 0.18 0.18 WPRO B1 0.19 0.19

EMRO D 0.18 0.18 WPRO B2 0.17 0.19

EURO A 0.13 0.13 WPRO B3 0.17 0.19

EURO B1 0.13 0.13

6. Regional incidence and prevalence estimates Tables 6.1 and 6.2 summarise the data and assumptions used to estimate regional prevalence rates for children and adults. For those regions with no available hearing loss prevalence studies, prevalence rates were assumed to be similar to other selected regions.

Table 6.1 Data and assumptions used to estimate regional prevalence rates for child-onset hearing loss

AFRO D and E From Nigeria study. Prevalences for 26+ dB assumed similar to SEARO D

AMRO A Based on prevalences estimated for WPRO A and NHANES III data

AMRO B and D Based on prevalences estimated for WPRO A, NHANES III and HHANES

EMRO B and D Prevalences from Oman study. For 81+ dB, assume similar to other regions

EURO A Based on study prevalences, plus other studies of congenital deafness and childhood deafness

EURO B1 and C Assumed the same as Euro A

EURO B2 Based on average of prevalences for Euro B1 and Emro B

SEARO B Average for India, Indonesia and Vietnam. Prevalences for 26+ dBHTL based on application of India ratios 26+/41+to average for 41+ from the three studies

SEARO D Based on India (Vellore 2). Prevalences for 26+ dBHTL based on average of India (urban) and India (rural) ratios of 26+/41+ applied to 41+ prevalences

WPRO A Based on Australian study

WPRO B1 Weighted average of China, Korea and Vietnam data. Inclusion of Vietnam to represent southern and rural areas of China.


WPRO B2 Based on average of Indonesia, Myanmar, Vietnam and India. As Indonesia and Myanmar have very high prevalences, conservative estimates were made giving these lower weight in the average. Prevalences for 26+ dBHTL based on application of India ratios 26+/41+ to 41+ prevalences

WPRO B3 No information. Have used an average of WPRO B1/B2 and SEARO B/D plus (0.5) weighted AFRO.


Table 6.2 Data and assumptions used to estimate regional prevalence rates for adults

AFRO D and E Based on Nigerian study

AMRO A Based on NHANES (using information also from Beaver Dam)

AMRO B and D Based on Hispanic HANES

EMRO B and D Based on Oman

EURO A Population-weighted average of prevalences for Britain, Italy, Denmark and Finland

EURO B1 and C Assumed the same as Euro A

EURO B2 Based on average of prevalences for Euro B1 and Emro B

SEARO B Average for India, Indonesia and Vietnam. Prevalences for 26+ dBHTL based on application of India ratios 26+/41+to average for 41+ from the three studies

SEARO D Based on India (Vellore 2). Prevalences for 26+ dBHTL based on average of India (urban) and India (rural) ratios of 26+/41+ applied to 41+ prevalences

WPRO A Based on Australian study

WPRO B1 Weighted average of China, Korea and Vietnam data. Inclusion of Vietnam to represent southern and rural areas of China.

WPRO B2 Based on average of Indonesia, Myanmar, Vietnam and India. As Indonesia and Myanmar have very high prevalences, conservative estimates were made giving these lower weight in the average. Prevalences for 26+ dBHTL based on application of India ratios 26+/41+ to 41+ prevalences

WPRO B3 No information. Have used an average of WPRO B1/B2 and SEARO B/D plus (0.5) weighted AFRO.

The resulting overall global prevalences of hearing loss at various threshold levels are shown below in Table 6.3. There are an estimated 588 million persons (including children) with mild or greater hearing loss globally, an estimated 248 million with moderate or greater hearing loss, and 53 million with severe or profound hearing loss. Figure 6.1 shows the resulting regional prevalences for moderate or greater hearing loss and the age-specific prevalence rates by regional groupings.

Table 6.3 Estimated global prevalence of hearing loss, GBD 2000 (Version 2)

Severity (dBHTL) Males Females Persons

Miild or greater (26+)

Adult-onset 215 197 413

Child-onset 89 86 175

Total 304 284 588

Moderate or greater (41+)


Child-onset 31 31 61

Total 125 123 248

Severe or greater (61+)



Child-onset 3 3 7

Total 24 29 53

Profound (81+)

Adult-onset 3 5 8

Child-onset 3 3 6

Total 6 8 14


Prevalence - Males

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

AFRO D - 1

AFRO E - 2

AMRO A - 3

AMRO B - 4

AMRO D - 5

EMRO B - 6

EMRO D - 7

EURO A - 8

EURO B1 - 9

EURO B2 -10

EURO C -11

SEARO B -12

SEARO D -13

WPRO A -14

WPRO B1-15

WPRO B2-16

WPRO B3-17

Age-std prevalence/100,000

Prevalence - Females

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

AFRO D - 1

AFRO E - 2

AMRO A - 3

AMRO B - 4

AMRO D - 5

EMRO B - 6

EMRO D - 7

EURO A - 8

EURO B1 - 9

EURO B2 -10

EURO C -11

SEARO B -12

SEARO D -13

WPRO A -14

WPRO B1-15

WPRO B2-16

WPRO B3-17

Age-std prevalence/100,000

Males

0

10000

20000

30000

40000

50000

60000

70000

0-4 5-14 15-29 30-44 45-59 60-69 70-79 80+

Age groups

Pre

vale

nce/

100,

000

A Regions

AMRO BD

EURO BC

EMRO

SEARO

WPRO B

AFRO

Females

0

10000

20000

30000

40000

50000

60000

0-4 5-14 15-29 30-44 45-59 60-69 70-79 80+

Age groups

Pre

vale

nce/

100,

000

A Regions

AMRO BD

EURO BC

EMRO

SEARO

WPRO B

AFRO

Figure 6.1. Estimated adult-onset hearing loss prevalence rates, 41+ dBHTL, by region and sex, GBD 2000 Version 2.


Table 6.3. Adult-onset hearing loss (41+ dBHTL): age-standardized incidence and prevalence estimates for WHO epidemiological subregions, 2000.

Age-std. Incidence/100,000 Age-std. prevalence/100,000

Subregion Males Females Males Females

AFRO D 213.8 167.8 3466.8 2919.3

AFRO E 203.9 169.2 3451.1 2976.7

AMRO A 323.1 189.0 4351.5 2643.0

AMRO B 264.7 150.1 3500.9 2119.8

AMRO D 260.3 150.8 3498.1 2107.9

EMRO B 324.2 281.3 4829.5 4200.5

EMRO D 322.8 279.1 4829.0 4241.4

EURO A 234.9 190.0 3337.6 2795.5

EURO B1 233.8 189.7 3301.7 2803.7

EURO B2 273.0 228.9 4037.9 3557.5

EURO C 274.8 235.0 4078.6 3561.7

SEARO B 421.8 336.7 6390.3 4901.9

SEARO D 363.2 360.0 5870.1 5827.1

WPRO A 243.1 187.7 2859.6 2685.9

WPRO B1 159.5 127.4 2567.5 2056.6

WPRO B2 430.7 346.4 6352.3 4506.2

WPRO B3 326.8 278.1 5081.0 4163.0

World 271.5 220.1 4036.3 3326.7

• Age-standardized to World Standard Population.


7. Global burden of adult-onset hearing loss in 2000 General methods used for the estimation of the global burden of disease are given elsewhere (50). The tables and graphs below summarise the global burden of adult-onset hearing loss estimates for the GBD 2000. Total global YLD for hearing loss are estimated to be 24.9 million or 4.7% of total YLD due to all causes. This makes hearing loss the second leading cause of YLD after depression, and gives it a larger non-fatal burden than alcohol use disorders, osteoarthritis and schizophrenia.

Table 7.1. Adult-onset hearing loss: YLD, YLL and DALY estimates by subregion, 2000.

YLD/100,000 YLL/100,000 YLD YLL DALY

Subregion Males Females Males Females (‘000) (‘000) (‘000)

AFRO D 304.2 299.8 0.0 0.0 1,008 0 1,008

AFRO E 301.6 285.6 0.0 0.0 991 0 991

AMRO A 475.1 357.4 0.0 0.0 1,286 0 1,286

AMRO B 277.7 222.7 0.0 0.0 1,106 0 1,106

AMRO D 221.4 171.4 0.0 0.0 140 0 140

EMRO B 409.5 358.1 0.0 0.0 537 0 537

EMRO D 383.0 399.5 0.0 0.0 540 0 540

EURO A 450.9 434.3 0.0 0.0 1,818 0 1,818

EURO B1 328.6 334.3 0.0 0.0 550 0 550

EURO B2 352.8 383.4 0.0 0.0 188 0 188

EURO C 479.0 550.8 0.0 0.0 1,271 0 1,271

SEARO B 570.0 453.7 0.0 0.0 2,019 0 2,019

SEARO D 514.4 551.3 0.0 0.0 7,177 0 7,177

WPRO A 337.0 451.6 0.0 0.0 591 0 591

WPRO B1 386.9 352.2 0.0 0.0 5,025 0 5,025

WPRO B2 479.7 427.9 0.0 0.0 644 0 644

WPRO B3 394.4 346.7 0.0 0.0 25 0 25

World 420.5 403.7 0.0 0.0 24,915 0 24,915

8. Conclusions These are version 3 estimates for the GBD 2000 as published in the World Health Report 2003. Apart from uncertainty analysis, updating estimates to reflect revisions of mortality estimates and any new or revised epidemiological data or evidence, it is not intended to undertake any major addition revision of these estimates.

We welcome comments and criticisms of these draft estimates, and information on additional sources of data and evidence.


Acknowledgements We particularly wish to thank Christina Bernard and Jennifer Wong for assistance with literature reviews, DISMOD analyses and preparation of this paper.


MALES - YLD per 1,000

0.00 1.00 2.00 3.00 4.00 5.00 6.00

EME - A regions

FSE - Euro B+C

IND - SEARO D

CHI - WPRO B1

OAI - SEARB+WPRB2/3

SSA - AFRO D+E

LAC - AMRO B+D

MEC - EMRO B+D

World

YLD/1000

GBD 2000

GBD 1990

FEMALES - YLD per 1,000

0.00 1.00 2.00 3.00 4.00 5.00 6.00

EME - A regions

FSE - Euro B+C

IND - SEARO D

CHI - WPRO B1

OAI - SEARB+WPRB2/3

SSA - AFRO D+E

LAC - AMRO B+D

MEC - EMRO B+D

World

YLD/1000

GBD 2000

GBD 1990

Figure 7.1. Adult-onset hearing loss YLD rates, by sex, broad regions, 1990 and 2000.


MALES - Global YLD per 1,000 by age

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0 20 40 60 80 100

YL

D/1

000

GBD 1990

GBD 2000

FEMALES - Global YLD per 1,000 by age

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0 20 40 60 80 100

YLD

/100

0

GBD 1990

GBD 2000

Figure 7.2. Global adult-onset hearing loss YLD rates, by age and sex, 1990 and 2000.


References

1. Murray CJL, Lopez, AD (eds.). The global burden of disease: a comprehensive

assessment of mortality and disability from diseases, injuries and risk factors in 1990 and projected to 2020. Cambridge, Harvard University Press (Global Burden of disease and Injury Series, Vol. 1) 1996

2. World Health Organization. World Health Report 2001. Mental health: New Understanding, New Hope. Geneva, World Health Organization 2001. Also available on the worldwide web at www.who.int/whr.

3. WHO Report of the Informal Working Group On Prevention Of Deafness And Hearing Impairment Programme Planning. Geneva, 1991

4. Duivestijn

5. Davis A Hearing In Adults The Prevalence And Distribution Of Hearing Impairment And Reported Hearing Disability In The MRC Institute Of Hearing Research´s National Study Of Hearing. London 1994.

6. Davis AC The Prevalence Of Hearing Impairment And Reported Hearing Disability Among Adults In Great Britain 1989

7. Quaranta A, Assennato G, Sallustio V. Epidemiology of hearing problems among adults in Italy. Scandinavian Audiology 1996;Supplementum. 42:9-13.

8. Parving A, Biering-Sorensen M, Bech B, Christensen B, Sorensen MS Hearing In The Elderly Greater Than 80 Years Of Age: Prevalence Of Problems And Sensitivity 1997 Scandinavian Audiology Vol 26(2), 99-106

9. Karlsmose B, Lauritzen T, Parving A. Prevalence of hearing impairment and subjective hearing problems in a rural Danish population aged 31-50 years. British Journal of Audiology 1999;33(6):395-402.

10. Uimonen S, Huttunen K, Jounio-Ervasti K, Sorri M. Do we know the real need for hearing rehabilitation at the popula tion level? Hearing impairments in the 5- to 75-year-old cross-sectional Finnish population. British Journal of Audiology 1999;33(1):53-9.

11. Moscicki EK, Elkins EF, Baum HM, Mcnamara PM Hearing Loss In The Elderly: An Epidemiologic Study Of The Framingham Heart Study Cohort 1985 Ear & Hearing Vol 6(4), 184-90

12. Cruickshanks K, Klein R, Klein B, Wiley T, Nondahl D, Tweed T Cigarette Smoking And Hearing Loss: The Epidemiology Of Hearing Loss Study 1998 JAMA Vol 279(21), 1715-19

13. Cruickshanks K, Klein R, Klein B, Wiley T, Nondahl D, Tweed T, Mares-Perlman JA, Nondahl DM Prevalence Of Hearing Loss In Older Adults In Beaver Dam, Wisconsin: The Epidemiology Of Hearing Loss Study 1998 American Journal Of Epidemiology Vol 148(9), 879-86

14. Dalton D, Cruickshanks K, Klein R, Klein B, Wiley T Association Of NIDDM And Hearing Loss 1998 Diabetes Care Vol21(9), 1540-1544

15. Popelka M, Cruickshanks K, Wiley T, Tweed T, Klein B, Klein R Low Prevalence Of Hearing Aid Use Among Older Adults With Hearing Loss: The Epidemiology Of Hearing Loss Study 1998 Journal Of The American Geriatrics Society Vol 46(9), 1075-78

16. Popelka M, Cruickshanks K, Wiley T, Tweed T, Klein B, Klein R, Nodahl D Moderate Alcohol Consumption And Hearing Loss: A Protective Effect 2000 Journal Of The American Geriatrics Society Vol 48(10), 1273-78


17. Reuben DBHL Hearing Loss In Community-Dwelling Older Persons: National Prevalence Data And Identification Using Simple Questions 1998 Journal Of The American Geriatrics Society Vol 46(8),1008-1011

18. Reuben DBHL Prognostic Value Of Sensory Impairment In Older Persons 1999 Journal Of The American Geriatrics Society Vol 47(8), 930-935

19. Lee DJ, Carlson DL, Lee HM, Ray LA, Markides KS. Hearing loss and hearing aid use in Hispanic adults: results from the Hispanic Health and Nutrition Examination Survey. American Journal of Public Health 1991;81(11):1471-4.

20. Beria J. Prevalence of deafness and hearing impairment: Preliminary results of a population - based study in southern Brazil. Informal Consultation on Epidemiology of Deafness and Hearing Impairment in Developing Countries and Update of the Who Protocol. WHO, Geneva, March 2003.

21. Wilson DH, Walsh PG, Sanchez L, Davis AC, Taylor AW, Tucker G, Meagher I The Epidemiology Of Hearing Impairment In An Australian Adult Population 1999 Int J Epidemiol Vol 28, 247-252

22. Khabori M, Mohammed AJ, Khandekar R, Prakesh N. National survey for causes of deafness and common ear disorders in Oman. Oman Ear Study (OES '96) survey report. Sultanate of Oman Ministry of Health; World Health Organization; 1996.

23. WHO-Regional Office For South-East Asia Multicentre Study On The Magnitude And Etiology Of Hearing Impairment Report Of A Meeting Of Principal Investigators Colombo, Sri Lanka, 3-5 September 1997

24. Joseph A. WHO-Sponsored Multicentric Study On Hearing Impairment. Singh AP, Chandra MR, Dayal D, Chandra R, Bhushan V Prevalence of deafness in a rural population of Lucknow District 1980 Indian J Public Health Vol XXIV, N 1 23-51

25. Jitendra P, Bhatia ML, Prasad BG, Dayal D, Jain PC Deafness among the urban community: And epidemiological survey at Lucknow (UP) 1974 Indian J Med Res 62,6, June 1974

26. Little P, Bridges A, Guragain R, Friedman D, Prasad R, Weir N Hearing Impairment and ear pathology in Nepal 1993 The Journal of Laryngology and Otology, Vol 107,395-400

27. Liu X, Xu L, Zhang S, Xu Y. Prevalence and aetiology of profound deafness in the general population of Sichuan, China. 1993, J Laryngol Otol Vol 107(11): 990-3

28. Bu X. Report of the pilot study on WHO Ear and Hearing Disorders survey protocol, Jiangsu Province China, - report. Nanjing Medical University 2002.

29. Bu X. The Report of Results from the Pilot Study on WHO Ear and Hearing Disorders Survey Protocol in Jiangsu Province, China. Informal Consultation on Epidemiology of Deafness and Hearing Impairment in Developing Countries and Update of the Who Protocol. WHO, Geneva, March 2003.

30. Kim HN, Kim SG, Lee HK, Ohrr H, Moon SK, Chi J et al. Incidence of presbycusis of Korean populations in Seoul, Kyunggi and Kangwon provinces. Journal of Korean Medical Science 2000;15(5):580-4.

31. Prasansuk S. Incidence/prevalence of sensorineural hearing impairment in Thailand and Southeast Asia. Audiology 2000;39(4):207-11.

32. Dung TT, Cio PT, Thuy NB. Nguyen bich thuy. Preliminary result of survey “Ear and Hearing disorder” in Vietnam. Informal Consultation on Epidemiology of Deafness and Hearing Impairment in Developing Countries and Update of the Who Protocol. WHO, Geneva, March 2003.

33. Nwawolo CC. The WHO Ear and Hearing Disorders Survey Protocol: Practical Challenges in its use in a Developing Country(Nigeria). Informal Consultation on Epidemiology of Deafness


and Hearing Impairment in Developing Countries and Update of the Who Protocol. WHO, Geneva, March 2003.

34. Davidson J, Hyde ML, Alberti PW. Epidemiology of hearing impairment in childhood. Scandinavian Audiology 1988;Supplementum. 30:13-20.

35. Fortnum H, Davis A. Epidemiology of permanent childhood hearing impairment in Trent Region, 1985-1993. British Journal of Audiology 1997;31(6):409-46.

36. Van Naarden K, Decoufle P, Caldwell K. Prevalence and characteristics of children with serious hearing impairment in metropolitan Atlanta, 1991-1993. Pediatrics 1999;103(3):570-5.

37. Lee DJ, Gomez-Marin O, Lee HM. Prevalence of childhood hearing loss. The Hispanic Health and Nutrition Examination Survey and the National Health and Nutrition Examination Survey II. American Journal of Epidemiology 1996;144(5):442-9.

38. Niskar AS, Kieszak SM, Holmes A, Esteban E, Rubin C, Brody DJ. Prevalence of hearing loss among children 6 to 19 years of age: the Third National Health and Nutrition Examination Survey. JAMA 1998;279(14):1071-5

39. Seely DR, Gloyd SS, Wright AD, Norton SJ. Hearing loss prevalence and risk factors among Sierra Leonean children. Archives of Otolaryngology -- Head & Neck Surgery 1995;121(8):853-8.

40. Jones ME. Auditory acuity in rural Africans: a selected study. Central African Journal of Medicine 1974;20(11):221-6.

41. Hatcher J, Smith A, Mackenzie I, Thompson S, Bal I, Macharia I et al. A prevalence study of ear problems in school children in Kiambu district, Kenya, May 1992. International Journal of Pediatric Otorhinolaryngology 1995;33(3):197-205.

42. Bastos I, Mallya J, Ingvarsson L, Reimer A, Andreasson L. Middle ear disease and hearing impairment in northern Tanzania. A prevalence study of schoolchildren in the Moshi and Monduli districts. International Journal of Pediatric Otorhinolaryngology 1995;32(1):1-12

43. Prescott CA, Kibel MA. Ear and hearing disorders in rural grade 2 (Sub B) schoolchildren in the western Cape. South African Medical Journal 1991;79(2):90-3.

44. McPherson B, Swart SM. Childhood hearing loss in sub-Saharan Africa: a review and recommendations. International Journal of Pediatric Otorhinolaryngology 1997;40(1):1-18.

45. Zakzouk SM. Epidemiological Study of Childhood Hearing Impairment in Saudi Arabia. Informal Consultation on Epidemiology of Deafness and Hearing Impairment in Developing Countries and Update of the Who Protocol. WHO, Geneva, March 2003.

46. Mui S, Reuben D, Damesyn M, Greendale G, Moore A Sensory Impairment As A Predictor Of 10-Year Mortality And Functional Impairment 1998 J Am Geriatr Soc Vol 46(9), 19-20.

47. Stouthard M, Essink-Bot M, Bonsel G, Barendregt J & Kramers P 1997. Disability weights for diseases in the Netherlands. Rotterdam: Department of Public Health, Erasmus University.

48. Mathers CD, Vos T, Stevenson C. The burden of disease and injury in Australia. Australian Institute of Health and Welfare, Canberra: AIHW, 1999.

49. WHO Hearing Aids Services: Needs And Technology Assessment For Developing Countries. Report Of A WHO/CBM Workshop. 24-26 November 1998.

50. Abutan BB, Hoes AW, Van Dalsen CL, Verschuure J, Prins A Prevalence Of Hearing Impairment And Hearing Complaints In Older Adults: A Study In General Practice 1993 Family Practice Vol 10(4), 391-5

51. Battey J Hearing Impairment Data 1999 Public Health Reports Vol 114(5),393

52. Carabellese C, Apollonio I, Rozzini R, Bianchetti A, Frisoni GB, Frattola L, Trabucchi M Sensory Impairment And Quality Of Life In A Community Elderly Population 1993 Journal Of The American Geriatrics Society Vol 41(4),401-7


53. Chmiel R, Jerger J Hearing Aid Use, Central Auditory Disorder, And Hearing Handicap In Elderly Persons 1996 Journal Of The American Academy Of Audiology Vol 7(3), 190-202

54. Cohn SE Hearing Loss With Aging:Presbycusis Clinics In Geriatric Medicine 1999 Vol 15(1),145-61

55. De Graaf R, Knippers EW, Bijl RV Prevalence And Relevant Background Characteristics Of Deafness And Severe Hearing Loss In The Netherlands 1998 Nederlands Tijdschrift Voor Geneeskunde Vol 142 (32), 1819-23

56. Furuta H, Yoshino T The Present Situation Of The Use Of Hearing Aids In Rural Areas Of Sri Lanka:Problems And Future Prospects 1998 International Journal Of Rehabilitation Research Vol 21(1), 103-7

57. Gates GA, Cooper JC, Kannel WB, Miller NJ Hearing In The Elderly: The Framingham Cohort, 1983-1985. Part I. Basic Audiometric Tests Results 1990 Ear & Hearing Vol (11)(4),247-56

58. Gates GA, Cooper JC, Kannel WB, Miller NJ Hearing In The Elderly:The Framingham Cohort, 1983-1985. Part I. Basic Audiometric Test Results 1990 Ear & Hearing Vol 11(4),247-56

59. Hearing Report: New Zealand Board Of Health. 1984

60. Jerger J, Chmiel R, Wilson N, Luchi R Hearing Impairment In Older Adults: New Concepts 1995 Journal Of The American Geriatrics Society Vol 43(8),928-35

61. Kerr AG Otolaringology Fifth Edition

62. Kllein AJ, Weber PC Hearing Aids 1999 Medical Clinics Of North America Vol 83(1), 139-51

63. Maggi S, Minicuci N, Martini A, Langlois J, Siviero P, Pavan M, Enzi G Prevalence Rates Of Hearing Impairment And Comorbid Conditions In Older People: The Veneto Study 1998 J Am Geriatr Soc, Vol 46(9), 10-69-74

64. Meecham E Audiolgy And Hearing Impairment: Improving The Quality Of Care 1999 Nursing Standard Vol 13(43), 42-46

65. Nadol J Medical Progress: Hearing Loss N Engl J Med 1993 Vol 329(15), 1092-1102

66. Reeves DJ, Alborz A, Hickson FS, Bamford JM, Gosden T Community Provision Of Hearing Aids And Related Audiology Services 2000 Health Technology Assessment Vol 4(4), 1-120

67. Rosenhall U, Jonsson R, Soderlind O Self-Assessed Hearing Problems In Sweden: A Demographic Study 1999 Audiology Vol 38(6), 328-34

68. Schein J Deafness In Canada And United States 1994 Deaf American

69. Steel K New Interventions In Hearing Impairment 2000 BMJ Vol 320(7235), 622-625.

70. Mathers CD, Stein C, Tomijima N, Ma Fat D, Rao C, Inoue M, Lopez AD, Murray CJL. (2002). Global Burden of Disease 2000: Version 2 methods and results. Geneva, World Health Organization (GPE Discussion Paper No. 50).

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