The study objective was to identify predictive criteria of severe non-traumatic secondary headache among the information gathered during telephone interview conducted by the on-call regulating physician at the Centre15.

Headache accounted for 1% of outpatient consultations, 2% of hospital emergency department visits and, at the French national level, 1% of complaints motivating calls to the prehospital emergency medical service units (The French, physician-led Emergency Calls Centers , called either "Center 15" or Service d'Aide Médicale d'Urgence [SAMU]). In 2009, the French "SAMU-Urgences de France" society proposed a classification and diagnostic tool for evaluating the headache patient, which is yet to be validated by a clinical study. Most patients with headache spontaneously consulted the emergency department (ED) and only 4 to 5% of patients entered ED through ambulance, fire and rescue department, medicalized ambulance (SMUR), or police. Patients attending emergency service for unusual sudden headache arriving by ambulance had a higher frequency of subarachnoid haemorrhage.

Headache studies have mainly been conducted in the ED. The Ottawa rule published by Perry et al. in 2013 proposed criteria for conducting explorations for subarachnoid hemorrhage (SAH) in patients over 15 years of age with severe, non-traumatic headache, having reached maximum intensity within one hour.

Unlike the primary headaches, secondary headaches are associated with underlying causes. Among the severe secondary headaches (SSH) (4 to 5% of headaches), non-traumatic subarachnoid haemorrhage was not diagnosed in 5.4% to 12% of cases in ED resulting in increase in mortality from 5 to 14%.

In 2018, French guidelines for the emergency management of headache recognized criteria likely to be at risk of Severe Secondary Headache, requiring explorations in emergencies for sudden headaches or thunderclaps headaches (i.e. reaching maximum intensity in less than a minute), recent headaches or progressive worsening (<7 days) and unusual, association with fever (apart from an obvious cause), association with signs of neurological impairment, suspicion of carbon monoxide poisoning, immunosuppression (neoplasia, HIV). Any unusual headache in a patient with recurrent paroxysmal or chronic headache should be considered secondary until proven otherwise. Subarachnoid hemorrhages were present in 11% of patients with sudden, intense and unusual headache.

In the French department of Loiret, patients with subarachnoid haemorrhage required a transfer out of the department to the nearest regional referral teaching hospital, by lack of adequate equipment and expertise for interventional neurology. Early diagnosis was therefore critical. In fact, an untreated cerebral aneurysm rupture increased bleeding recurrence by 3-4% in the first 24 hours.

Inclusion Criteria:

• Telephone call from center 15 for the headache pattern
• Age ≥ 18
• Non-opposition expressed by the patient
• Or non-opposition delayed (adults with cognitive disorders, protected adults, clinical situations judged to be serious by the Medical Regulation Assistant, physician regulator, incoming call flow, call by close or trusted person)

Exclusion Criteria:

• Head trauma < 48 hours
• Moribund patient
• Non-affiliation to a social security scheme
• Opposition to the continuation of the study expressed orally by the patient or by return mail within 30 days

The patients presenting all the inclusion criteria and not showing any of the non-inclusion criteria will be included prospectively and consecutively when calling for medical regulation from the SAMU 45. The patients will be included in the study by the doctor regulator.