{'fraction_non_alphanumeric': 0.025152439024390245, 'fraction_numerical': 0.03125, 'mean_word_length': 5.282296650717703, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Observed and expected prevalence of permanent childhood hearing impairment in Oldham.

BACKGROUND
A perceived high prevalence of permanent childhood hearing impairment in Oldham, particularly in the Asian community, caused concern during the local implementation of the Newborn Hearing Screening Programme.


METHODS
A retrospective cohort study of cases with dates of birth between 1 January 1986 and 31 May 2003 was undertaken to describe local epidemiology and establish the observed prevalence rate. Expected prevalence was determined by application of published national rates to the susceptible Oldham population.


RESULTS
The study identified 132 children in Oldham meeting the case definition. The prevalence of permanent childhood hearing impairment in the non-Asian community (1.34/1,000 live births) was equal to published national rates (1.33/1,000 live births), but that in the Asian community (4.64/1,000 live births) indicated a relative risk of 3.5. Differences in prevalence between observed and expected rates was greater than would have occurred by chance (p<0.001).


CONCLUSION
The clinical suspicion of a raised local prevalence of permanent childhood hearing impairment in Oldham was confirmed. The importance of using locally derived data when implementing national policy is emphasized.