The following table summarises prevalence estimates for obstructive sleep apnoea syndrome and insomnia among New Zealand adults, based on our national surveys.
Obstructive Sleep Apnoea Syndrome (OSAS)
a OSAS was defined as having a respiratory disturbance index ≥ 5 and ESS > 10. These are conservative prevalence estimates based on data collected in 1991-2001 and prevalence will have increased with increasing obesity rates. In the 2013-2014 National Health Survey (13,309 adults aged 18+ y), only 1.9% of participants had been diagnosed with obstructive sleep apnoea (John McCarthy, personal communication).
An economic analysis based on these data and treatment services in Wellington in 2005 estimated that the total annual societal costs of OSAS for New Zealanders aged 30–59 y were $40 million ($419 per case), with accidents being the major contributor. The incremental net direct medical cost per quality of life year (QALY) gained with successful treatment was $94. (This is the difference between the cost of treating and the cost of not treating). By comparison, the average cost for new drugs funded by PHARMAC in 2004/05 was $6,865 per QALY gained. These analyses strongly support the cost effectiveness of treating OSAS.
Insomnia
b Based the 2001 insomnia survey, it was estimated that 13% of New Zealanders aged 20-59 y (2.317 million people in 2008) had insomnia. In the survey, Māori were more likely than non-Māori to report the common insomnia and to experience excessive daytime sleepiness. An economic analysis based on these data estimated the total annual societal costs of insomnia for New Zealanders aged 20–59 y were $28.4 million ($628 per case) and that successful insomnia treatment would save $21.8 million per year. The incremental net saving per quality of life year (QALY) gained with successful treatment was $3,9072. (This is the difference between the cost of treating and the cost of not treating). These analyses indicate that effective insomnia treatment would save money as well as improving the health, safety, and quality of life of many New Zealanders.
However, there is not yet a systematic diagnostic pathway or funding for treatment of insomnia in the public healthcare sector. In the 2013-2014 National Health Survey (13,309 adults aged 18+ y), only 3.4 % of participants had been diagnosed with insomnia (John McCarthy, personal communication).
Narcolepsy
People with narcolepsy experience excessive daytime sleepiness that can occur with or without cataplexy (a sudden episode of muscle weakness often triggered by intense emotional responses). Additional symptoms may include automatic behaviour, disrupted night-time sleep, sleep paralysis and hallucinations when falling asleep or waking up.
A survey sent to members of the Narcolepsy Support Group, sleep physicians, neurologists and sleep laboratories (67 responses) confirmed that New Zealanders with narcolepsy report significantly higher daytime sleepiness, and lower quality of life, than the general New Zealand population. The majority of patients reported that narcolepsy prevented them from or caused difficulty in doing everyday activities; prevented them from communicating, mixing or socialising with others; had contributed to leaving school or a job; and contributed to injuries of themselves or other people. Most patients reported an onset of symptoms in their early 20s, although diagnosis was on average delayed by a decade. Diagnosis was made by a wide range of clinicians but for most patients, had not involved objective diagnosis (an overnight sleep study or multiple sleep latency test (MSLT)). The majority of patients were taking medication to treat narcolepsy, including stimulant medication and REM-suppressant antidepressants.
This small study highlighted inconsistencies in the diagnosis and treatment of New Zealand patients with narcolepsy, which likely reflects the state of the science at the time of individual diagnosis (patients were diagnosed on average 20 years before completing the study questionnaire).
