PUBLIC INSURANCE FOR NOISE-INDUCED HEARING LOSS

Transcription

1 PUBLIC INSURANCE FOR NOISE-INDUCED HEARING LOSS Luciano Bindi, Marta Clemente, Angela Goggiamani INAIL Italian Workers Compensation Authority General Medical Department P.le G.Pastore 6, Roma, Italy Roberto Piccioni, Giuseppe Rosci INAIL Italian Workers Compensation Authority Technical Directorate for Risk Assessment P.le G.Pastore 6, Roma, Italy; Hearing loss due to extended noise exposure is still an important issue, in spite of the new legislation and the greater public awareness, which have brought about an improvement in the behaviour of employers through the adoption of progressive preventive and protective measures. In these last few years, the acoustic climate in our living environment has deteriorated, introducing an important confounder that makes occupational hearing loss assessment extremely complicated. This paper illustrates the different aspects of noise-related risk analysis and the insurance assessment procedure in occupational hearing loss. The procedure includes the following steps: -The risk assessment of occupational hearing loss; -The medical legal assessment, including the clinical diagnosis, the causal relationship with working conditions and the compensation to be paid. Over the last few years, progress has been made in legislation and technical equipment and more accurate instruments are now available for risk assessment, together with more detailed technical regulations and more specific predictive models. This paper provides an overview of the current situation, putting the emphasis on a number of critical issues. ICSV22, Florence (Italy) July

2 1. Introduction Noise-induced hearing loss is still one of the most common and important occupational diseases. However, in the last few years a reduction in incidence has been observed. In fact, until 2005 noiseinduced hearing loss was ranking first in the list of occupational diseases reported in Italy, but since 2006 musculoskeletal disorders have become number one occupational diseases. This reversal of trend is undoubtedly due to the inclusion of musculoskeletal disorders in the new table of occupational diseases introduced by Ministerial Decree of 9 April 2008, which promoted recognition and encouraged awareness in this area. However, it is worth mentioning that noise-induced hearing loss (NIHL) is still one of the most commonly reported occupational diseases. Noise is a risk factor that can cause short and long-term and even chronic health impairment and particularly affects the hearing system. The main consequence is the noise-induced hearing loss, a disease caused by exposure to highintensity noise that can lead to hearing impairment and functional loss. Occasionally, non-hearing-related effects can be observed on other systems as a consequence of noise-exposure (especially the nervous system, the cardiovascular and the digestive systems). Temporary or continuous and prolonged exposure of the hearing apparatus to low and medium intensity noise can damage the cochlea due to metabolic fatigue and direct mechanical action and can damage the cyto-archtecture of the organ of Corti and cause degeneration of ganglion cells and nerve fibers in the area. The human ear is able to perceive a broad range of sound pressure variations from 0 db (20 µpa), the so-called threshold of hearing, to 140 db (200 Pa), which is the threshold of pain, and a frequency spectrum between 20 and Hz. Noise-induced hearing loss can develop after exposure to very high-intensity instant noises or after constant and prolonged exposure to acoustic stimuli of given quality, intensity and length. Hearing loss caused by chronic acoustic injury is generally defined by the prolonged occupational exposure to sound levels above 80 db. As regards insurance and workers compensation, hearing impairment can be classified in different ways, depending on whether it has been induced by acute acoustic injury or by occupational exposure in a noisy environment. In the former case, it will be considered as work-related accident, while in the latter as an occupational disease. 2. INAIL - Italian Workers Compensation Authority s procedure on occupational hearing loss compensation INAIL s position on occupational diseases tends to differ depending on whether they have been included or not in the Tables introduced by the above mentioned Ministerial Decree, which was last updated on 9 April In particular, before 1988, coverage of occupational diseases was only granted to those included in the above tables, in compliance with the principle of legal presumption of origin. After two rulings issued by the Constitutional Court (ruling n.179 of 10 February 1988 and ruling n.206 of 11 ICSV22, Florence, Italy, July

3 February 1988), insurance coverage has been extended also to occupational diseases not listed in the tables (either as medical conditions or working processes), provided the occupational nature of the disease could be demonstrated. For unlisted occupational diseases it is up to the workers to prove the causal relationship with the type of working activity performed 1. As regards noise-induced hearing loss, the new Tables include a longer list of tasks that can give rise to legal presumption of origin. This increase in number of listed eligible tasks becomes all the more relevant if we consider the last item, which includes all non-occasional tasks which entail personal, daily or weekly exposure to more than 80 db (A). In the table concerning Industry, the following description is included: Performance of tasks which entail noise exposure with no effective sound protection. This point may raise problems during risk investigation and assessment, as the professionals in charge of risk assessment (CONTARP) cannot rely on technical guidelines to follow in the investigation process. An additional important legal reference is provided by ruling 3476 of 1994 by the Court of Cassation, (the court of last resort in Italy) which introduced the principle of environmental risk, on account of which insurance coverage is extended also to occupational events amenable to hazards on the workplace. All the above highlights that recognition of this particular disease must be based on accurate assessment of a multiplicity of factors. Therefore, it can be concluded that for the diagnosis of noise-induced hearing loss as an occupational disease two fundamental requirements have to be met for workers compensation to be awarded: - Occupational exposure to a potentially hazardous noise, in terms of quality, intensity and duration; - Compatibility of the reported condition with the characteristics of occupational hearing loss. 3. Noise exposure risk assessment Noise exposure risk assessment is particularly challenging as previous occupational history has to be collected often ranging over a period of years. Hence the importance of an extremely detailed occupational history and an accurate description of the working activities performed by the claimant, in terms of tasks, equipment, machine and tools used. Whenever possible a description should be provided of the corresponding environmental conditions and the time spent on different tasks and processes. In the first phase, detailed information shall be collected on the activity performed by the worker. To this purpose, reference shall be made to the documentation available at the company or the companies where the claimant has been employed, if any. In particular, the Risk Assessment Document must be taken into account, together with noise hazard assessment. As regards this point, it is worth mentioning that noise was one of the first occupational risks to be considered, as provided for by the law since the introduction of legislative Decree 277/1991. The examination of the above documentation will make it possible to trace the worker s previous occupational exposure, with reference to the two most important parameters: length of time in years and exposure level (daily or weekly). 1 As a matter of fact, INAIL is available to allocate professional and technological resources to collect objective evidence and obtain a realistic picture of the worker s probable exposure, also by performing inspections and measurements, whenever useful and necessary. ICSV22, Florence, Italy, July

4 Unfortunately, such reconstruction of facts is often made more difficult by the lack or inadequacy of risk assessment documents. In such instances, an approximate estimation can be made based on noisiness values related to the operation of specific machine and equipment, as provided by specialized studies or data banks (as established also by Legislative Decree 81/08, Art.190, Par. 5 bis) [1]. Moreover, the lack of data can be made up for by performing phonometric tests [2] in an occupational environment similar to the one experienced by the claimant during his working life (similar tasks, machines and equipment). Finally, in order to conduct an accurate assessment of exposure, concomitant occupational factors have to be taken into account, and in particular the concomitant exposure to vibrations and ototoxic substances (as expressly established in Leg. Decree D.Lgs. 81/08, Art. 190, Par. 1, Letter d). 4. Hearing loss diagnosis The following clinical examinations have to be performed to identify sensorineural hearing loss of a cochlear origin compatible with a diagnosis of noise-induced hearing loss: tone audiometry (subjective test) + impedance measurement (objective test). Tone audiometry is the most important hearing test, both from a clinical and a medical-legal point of view, and enables to assess the hearing threshold to simple stimuli such as pure tones, i.e. the tones that have one single vibration frequency, by testing air and bone conduction. In particular cases, BSERA (Brain stem electric response audiometry) and/or SVR (slow vertex response) can also be conducted. The definition of subjective test refers to those tests that elicit verbal or motor responses and are strictly dependant upon the will and determination of the examined subject, while objective tests are performed by analysing the electrophysiological effects or the reflected phenomena, in order to exclude any interference of subjective will, even if these tests require the patient s cooperation to prevent response artefacts. Occupational noise-induced hearing loss is characterized by bilateral, perceptive and symmetrical hearing loss, with maximum dip in the cochlear base area ( Hz) and a rise at about 8000 Hz, at least in the early phases. It is an irreversible hearing loss with no progression after stopping exposure, with recruitment almost always present. It is a perceptive hearing loss due to the impairment of acoustic cells at in the cochlear base. Once occurred, the damage is irreversible and, independently of its severity and the stage of disease, it causes an irreversible loss of hearing perception. Hearing loss after chronic acoustic injury progresses rapidly in the first years and then tends to slow down and stabilize with the passing of time The initial damage occurs at 4000 Hz and then extends to higher frequencies (3000 Hz first, and then 2000 Hz and 1000 Hz). The audiometric test shows a down-sloping curve with a rise in the hearing threshold at high and medium frequencies. A slight asymmetry can be observed between the right and the left ear with a threshold up to db, which can be the consequence of low-intensity noise exposure (i.e. can develop as a consequence of the worker s physical position at work) and be compatible with a diagnosis of chronic acoustic injury. ICSV22, Florence, Italy, July

5 Other non-occupational injuries can cause hearing loss and show audiometric tracings similar to chronic acoustic trauma: cardiovascular disease, head injury, ototoxic drugs (streptomycin, quinine, aspirin, antibiotics, aminoglycosides, diuretics, etc.), diabetes mellitus, viral infections, lipid profile alterations, neck injury, genetic disorders, renal failure, presbyacusis. Collecting an accurate occupational history is also important, together with a precise pathological history, in order to perform a differential diagnosis with the noise-induced hearing loss tracings. 5. Noise-induced impairment assessment When noise-induced hearing loss was listed among the occupational diseases eligible for compensation, the hearing impairment assessment proved to be challenging as, until the biological damage was provided for in Ministerial Decree D.M. 12/7/2000, there was no assessment table unanimously recognized by the law (in fact, the only reference percentage for permanent disability concerned monaural total hearing loss in Industry and Agriculture, with 15% and 20% respectively, and total bilateral hearing loss of 60%). This lead to extreme lack of uniformity in the assessment approach. Until 1992, the table by Rossi et al. was considered the only reference tool for a correct differential assessment in Industry and Agriculture. In order to overcome this lack of uniformity, in December 1991 the first agreement between Inail and Social Partners was signed, which introduced a single occupational hearing loss assessment table throughout the National territory [3], implemented by Inail circular letter n. 17 of 31/3/1992. Aim of the agreement was to ensure an organic and comprehensive coverage plan to workers affected by occupational hearing loss while, at the same time, providing the prototype for a strategy that was open to and aware of the social reality and increasingly inspired by principles of transparency, in the pursuit of total quality in service provision. Again in 1992, Inail implementing circular letter and rulings n.6846 and 7183 of the United Chambers of the Court of Cassation set forth a number of general principles on the assessment of noise-induced hearing loss that were adopted by Inail with the introduction of a revised table in Besides raising the hearing threshold on speech frequencies, the new Inail Social Partners Table of 1994 considered also hearing loss at the frequency of 4000 Hz, which is the first to be affected by noise, and attributed different scores to frequencies. The principle underlying the previous agreement, according to which adequate assessment of moderate and moderate to severe hearing loss was given priority remained basically unchanged, while the assessment of hearing loss characterized only by instrumental test alterations was substantially curbed, according to the principles outlined by the Court of Cassation (which set the new case law on this matter an increase in acoustic thresholds up to 25 db is to be considered normal and not related to occupational hearing impairment ). In the revised table, the assessment was carried out according to the following formula: Industry = (best hearing ear x 3) + worst hearing ear x Agriculture = best hearing ear x 2) + worst hearing ear x ICSV22, Florence, Italy, July

6 The Legislative Decree of February 23rd, 2000 n. 38, published on Gazzetta Ufficiale Serie Generale (official journal of record of the Italian government) n. 50 of titled Provisions on mandatory insurance against work accidents and occupational diseases, in compliance with art. 55, par. 1, of Law 17 May 1999 n. 144 and the introduction of biological damage assessment, changed de iure and de facto the legislation in force at the time. For the purpose of medical legal assessment, the table attached to Leg. Decree 38/2000 is used, with a percentage value allocated to total unilateral hearing loss equal to 12% (cod. 310), while total bilateral hearing loss is allocated a value of 50% (code 311). Consequently, the value attributed to total unilateral hearing loss is the expression of a one to four ratio (total uni lateral/total bilateral hearing loss). As regards the assessment of biological damage in partial bilateral hearing impairment (code 312), the following formula is applied: Biological damage = (best hearing ear x 4) + worst hearing ear x With this assessment process, unilateral hearing damage can be evaluated based on the assumption that hearing impairment is a de facto functional impairment of a sensory organ, where the descriptive definition of sensory organ includes a more extensive conceptual definition of the ear as a paired organ which is a functional entity and not only a mere anatomical entity on account of the paired function it performs with another organ morphologically equal in the other half on the body. Therefore, with respect to the hearing function, paired organs express an organic-functional system, i.e. an anatomical and functional system in which all anatomical structures perform the same sensory function. For the purpose of Inail assessment, and in compliance with Court of Cassation rulings, permanent hearing impairment is awarded when the mean hearing loss in frequencies of Hz is higher than 25 db. 6. Congruence of damage After calculating duration in years and worker s previous exposure level, the congruence is established between the damage identified during medical examination and previous worker s exposure: this operation may be fundamental especially in doubtful cases. To this purpose, reference can be made to Standard ISO 1999:1990 on the Determination of occupational noise exposure and estimate of noise-induced hearing loss. This Standard is still today the only damage predictive tool available: in fact, the standard provides a statistical calculation method of the permanent hearing threshold shift induced by continuous noise exposure NIPTS (Noise Induced Permanent Threshold Shift). NIPTS value is calculated in terms of odds ratio, due to the different individual sensitivity to noise exposure. For this reason, the above method cannot be used to estimate the expected individual damage, but can determine the probability that the diagnosed damage can occur in an individual exposed to a given noise level. Consequently, the result is expressed based on the statistical distribution of the reference population and the estimated hearing impairment in decibel (NIPTS) refers to a given population fractile. In order to distinguish age-related hearing loss (presbyacusis) from noise-related hearing loss, the standard takes into account the database of two types of population:: ICSV22, Florence, Italy, July

7 - A highly selected population with normal hearing (good health, no hearing symptoms, no noise exposure); - An unselected population of a typical industrialized society (including genetically predisposed subjects, subjects with hearing diseases, subjects exposed to non-occupation noise, etc.). The following values are calculated for both populations: - HTLA (Hearing threshold level associated with age) - HTLAN (Hearing threshold level associated with age and noise). In conclusion, congruence of damage can be estimated as a fractile value of a population that reaching a certain age and being exposed to occupation noise has developed a hearing threshold equal to or higher than the diagnosed hearing impairment at the tested frequencies. The population fractile limit must ensure adequate coverage to the insured worker in statistical and epidemiological terms. Pending more specific National guidelines and based on currently accredited criteria in the field of protection and prevention, this value could be estimated on the basis of a 95% confidence interval, i.e. a 5% fractile of the underlying population. Standard ISO 1999:1990 has two limitations. The first limitation is that the underlying statistical data refer to European and North American populations and are not specific for the Italian population that would provide a more accurate estimate of results. The second is that the standard only provides a single noise exposure level input value, which poses problems when the insured party performed different activities and tasks on the workplace and was exposed to different noise levels over the years. This challenge can be overcome by applying the equal energy principle and estimating a single exposure level with an energy value equivalent to the different exposure levels experienced by the insured party throughout the whole period. However, the above standard is by any means the only predictive tool available to estimate hearing impairment, until specific statistical and epidemiological data are collected for the Italian population. References 1 D.L.gs. 9 aprile 2008 n TESTO UNICO SULLA SALUTE E SICUREZZA SUL LA- VORO (Single Text of Occupational Health and Safety) 2 CEI EN Elettroacustica - Misuratori del livello sonoro (Electroacoustics - Sound level meters) 3 Caporale R., Bisceglia M., Le Ipoacusie da rumore in ambito INAIL - Inail Sovrintendenza medica Generale 2003 ICSV22, Florence, Italy, July