Mild head injury in New Zealand: incidence of injury and persisting symptoms.

AIMS: To define mild head injury and determine its incidence and that of persisting symptoms.

METHODS: Analysis of an eight week sample of all patients with head injury passing through the Emergency Departments of the four Auckland Hospitals, and of a five year sample of patients attending a clinic for management of symptoms persisting after head injury.

RESULTS: Mild head injury was defined by the acute management needed--care out of hospital or not more than 48 hours admission, corresponding reasonably with a definition using post-traumatic amnesia. Incidence in those seen at hospital was 437/10(5) whole population/year for ages 15 and over, and 252/10(5) for ages under 15. Age specific incidences were 1769/10(5)/year for 15 and over, and 2920/10(5) for ages under 15, the major causes being road accidents (RTA) and falls, respectively. For 100 cases seen at hospital approximately 60 were treated by general practitioners alone. Referrals in patients 15 years and over because of persisting symptoms occurred in 5% (95%, CI 3-7), 69% in the first four months and 6% after a year. Referrals were equally likely after RTA, sports injuries and assaults, more frequent after objects striking the head. Older people were marginally more likely to be referred and the probability was significantly greater in women injured in sport and in minor RTA not needing admission to hospital.

CONCLUSIONS: Mild head injuries are economically important and deserve efficient management.